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  • 1.
    Aitomäki, Yvonne
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Moreno, Sergio
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Vacuum infusion of cellulose nanofibre network composites: Influence of porosity on permeability and impregnation2016Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 95, s. 204-211Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Addressing issues around the processing of cellulose nanofibres (CNF) composites is important in establishing their use as sustainable, renewable polymer reinforcements. Here, CNF networks of different porosity were made with the aim of increasing their permeability and suitability for processing by vacuum infusion (VI). The CNF networks were infused with epoxy using two different strategies. The permeability, morphology and mechanical properties of the dry networks and the resulting nanocomposites were investigated. Calculated fill-times for CNF networks with 50% porosity were the shortest, but are only less than the gel-time of the epoxy if capillary effects are included. In experiments the CNF networks were clearly wetted. However low transparency indicated that impregnation was incomplete. The modulus and strength of the dry CNF networks increased rapidly with decreasing porosity, but their nanocomposites did not follow this trend, showing instead similar mechanical properties to each other. The results demonstrated that increasing the porosity of the CNF networks to ≈ 50% gives better impregnation resulting in a lower ultimate strength, a higher yield strength and no loss in modulus. Better use of the flow channels in the inherently layered CNF networks could potentially reduce void content in these nanocomposites and thus increase their mechanical properties.

  • 2.
    Aitomäki, Yvonne
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Moreno, Sergio
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Oksman, Kristiina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Vacuum Infusion of Nanocellulose Networks of Different Porosity2015Inngår i: 20th International Conference on Composite Materials: Copenhagen, 19-24th July 2015, ICCM , 2015, artikkel-id 4109-1Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Cellulose nanofibres (CNF) have shown good potential as sustainable, biobased reinforcing materials in polymer composites. Addressing issues around the processing of these composites is an important part of establishing their use in different applications. Here, CNF networks of different porosity are made from nanofibrillated hardwood kraft pulp with the aim of increasing the impregnation of the CNF networks and to allow vacuum infusion to be used. Two different vacuum infusion strategies: in-plane and out of plane were used to infuse the CNF networks with a low viscosity epoxy. The permeability, morphology and mechanical properties of the dry networks and the resulting nanocomposites were investigated and compared to a micro-fibre based network. Using the out-of-plane permeability measurements and Darcy’s law, the fill-time was calculated and showed that the CNF network with 40% porosity had the lowest fill-time when an out-of-plane impregnation strategy is used. However this exceeded the gel-time of the epoxy system. In experiments, the resin reached the other side of the network but low transparency indicated that wetting was poor. The dry CNF preforms showed a very strong dependence on the porosity with both modulus and strength increasing rapidly at low porosity. Interestingly, the composite based on the 60% porosity network showed good wetting particularly with the in-plane infusion strategy, exhibiting a much more brittle fracture and a high yield strength. This shows that in CNF composites produced by VI, lowering the fibre volume content of the CNF composites gives better impregnation resulting in a lower ultimate strength but higher yield strength and no loss in modulus.

    Fulltekst (pdf)
    fulltext
  • 3.
    Albihn, Johan
    Luleå tekniska universitet, Institutionen för ekonomi, teknik, konst och samhälle.
    Creative development of lightweight façade constructions in modular housing: The struggle to shut out the noise of the world2022Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    Modular construction of housing is an industry on the rise. The prefabrication of construction modules gives a greater control over material consumption, promotes standardization, and lessens the disturbance during the construction time in the field.

    Lindbäcks Bygg AB prefabricates housing modules in their factory at Haraholmen, Piteå. The modules are then transported to construction sites all over the country and assembled. Lindbäcks Bygg AB has made the design choice to focus on lightweight wooden constructions for their modules, which comes with its own set of challenges.

    The urban densification of our city regions has led to more and more residential building being planned and constructed in areas that are submitted to high noise levels from surrounding traffic. This puts a great strain on the sound reduction of the building’s façade wall construction, something that has proven to be a problem with lightweight wooden walls.

    The aim of this master thesis project has been to test different solutions for lightweight façade wall constructions, and to ultimately find one or more solution that meet the requirements of the Swedish standards and regulations, as well as the needs of the tenants, and that can be implemented by Lindbäcks Bygg AB for manufacturing and assembly.

    The project has therefore been carried out in two parts, one theoretical and one practical. The theoretical part has verified the problem with traffic noise levels in residential buildings and identified the critical areas of the current façade construction. The theoretical work led to a list of defining factors for the sound reduction, which in turn worked as a basis for the ideation process. 

    As a result, the theoretical part led to a number of different construction concepts for façade walls. The concepts were first tested theoretically through modelling and calculation, and verified with the acousticians at Tyréns Sverige AB and the engineers of Lindbäcks Bygg AB. The most promising concepts were sent on to be manufactured.

    The practical part of this master thesis project was carried out mainly as acoustical measurements and the subsequent analysis, where the manufactured façade wall constructions were mounted on a free-standing module.

    The result of the practical part, and of the master thesis project, were four different façade wall constructions that met the requirements for noise reduction, which were presented to Lindbäcks Bygg AB and Tyréns Sverige AB. The construction most easily implemented is a construction with an airgap between the wall panels, and this construction will now have to be structurally verified and adapted for the factory, before being utilized in future building projects.

    Fulltekst (pdf)
    fulltext
  • 4.
    Almqvist, Andreas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Fabricius, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Flow in thin domains with a microstructure: Lubrication and thin porous media2017Inngår i: AIP Conference Proceedings, ISSN 0094-243X, E-ISSN 1551-7616, Vol. 1798, artikkel-id 020172Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper is devoted to homogenization of different models of flow in thin domains with a microstructure. The focus is on applications connected to the effect of surface roughness in full film lubrication, but a parallel to flow in thin porous media is also discussed. Mathematical models of such flows naturally include two small parameters. One is connected to the fluid film thickness and the other to the microstructure. The corresponding asymptotic analysis is a delicate problem, since the result depends on how fast the two small parameters tend to zero relative to each other. We give a review of the current status in this area and point out some future challenges.

  • 5.
    Alnersson, Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Gestamp Hardtech.
    Towards 3D modelling of Compression Moulding of SMC2021Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The automotive industry is facing ever increasing demands for reduced emissions, and lightweight solutions are thusly required. One field that has significant potential in this regard is composite materials, which can offer a good combination of weight reduction and mechanical properties. However, the rapid development cycles in the automotive industry mean that tools for numerical modeling are necessary, both regarding manufacturing processes and prediction of mechanical properties. 

    The material that has been of interest for this work is Sheet Moulding Compound (SMC). SMC consists of sheets of resin and chopped fibres. When used for manufacturing the sheets are cut into appropriate size and shape. The cut sheets are then placed in a pre-heated mould. When this mould is closed, the sheets melt and the fibre-filled resin flows out and fills the mould cavity; the resin then cures and solidifies. A significant advantage of SMC compared to other composite solutions is that the process has comparatively short cycle times, which is a necessity for automotive applications. However, it is a rather complicated process to model numerically for a number of reasons, including the complex rheological properties of the charge, the often rather significant temperature gradients throughout the thickness, often complicated three-dimensional effects in the flow, and the chopped fibres present in the charge. These fibres will move and change orientation as the charge is pressed, which is a significant challenge to model properly.

    The first part of this work is a review and discussion of the difficulties described above, and some solutions that have been suggested. The second part concerns a suggestion for a three-dimensional flow model for the compression moulding process, which takes into account factors that have been suggested to influence the flow behavior, such as temperature distribution and shear strain rate. Some simulation results are presented along with comparison to previous experimental results, and similar flow patterns are observed serving as a qualitative validation. The third part concerns the expansion of this model to include the effects of the flow on the fibre orientation.

    Fulltekst (pdf)
    fulltext
  • 6.
    Alnersson, Gustaf
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Gestamp Hardtech, Sweden.
    Aitomäki, Yvonne
    RISE AB, Sweden.
    Ljung, Anna-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    3D Flow and Fibre Orientation Modelling of Compression Moulding of A-SMC: Simulation and Validation in Squeeze Flow2022Inngår i: ECCM 2022 - Proceedings of the 20th European Conference on Composite Materials: Composites Meet Sustainability / [ed] Vassilopoulos, Anastasios P.; Michaud, Véronique, EPFL Lausanne, Composite Construction Laboratory , 2022, Vol. 2, s. 250-255Konferansepaper (Fagfellevurdert)
    Fulltekst (pdf)
    fulltext
  • 7.
    Alnersson, Gustaf
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Gestamp Hardtech, Luleå, Sweden.
    Lejon, Erik
    Gestamp Hardtech, Luleå, Sweden.
    Zrida, Hana
    Gestamp Hardtech, Luleå, Sweden.
    Aitomäki, Yvonne
    RISE Sicomp, Öjebyn, Sweden.
    Ljung, Anna-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    3D flow and fibre orientation modelling of compression moulding of A-SMC: simulations and experimental validation in squeeze flow2023Inngår i: Functional Composite Materials, E-ISSN 2522-5774, Vol. 4, artikkel-id 11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sheet Moulding Compound (SMC) based composites have a large potential in industrial contexts due to the possibility of achieving comparatively short manufacturing times. It is however necessary to be able to numerically predict both mechanical properties as well as manufacturability of parts.

    In this paper a fully 3D, semi-empirical model based on fluid mechanics for the compression moulding of SMC is described and discussed, in which the fibres and the resin are modelled as a single, inseparable fluid with a viscosity that depends on volume fraction of fibres, shear strain rate and temperature. This model is applied to an advanced carbon-fibre SMC with a high fibre volume fraction (35%). Simulations are run on a model of a squeeze test rig, allowing comparison to experimental results from such a rig. The flow data generated by this model is then used as input for an Advani-Tucker type of model for the evolution of the fibre orientation during the pressing process. Numerical results are also obtained from the software 3DTimon. The resulting fibre orientation distributions are then compared to experimental results that are obtained from microscopy. The experimental measurement of the orientation tensors is performed using the Method of Ellipses. A new, automated, accurate and fast method for the ellipse fitting is developed using machine learning. For the studied case, comparison between the experimental results and numerical methods indicate that 3D Timon better captures the random orientation at the outer edges of the circular disc, while 3D CFD show larger agreement in terms of the out-of-plane component. One of the advantages of the new image technique is that less work is required to obtain microscope images with a quality good enough for the analysis.

    Fulltekst (pdf)
    fulltext
  • 8.
    Alnersson, Gustaf
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Ljung, Anna-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    3D-flow and and fibre orientation modelling for compression moulding of SMCManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Two different numerical models for compression moulding of Sheet Moulding Compound are discussed and compared, with one being a more traditional flow model implemented in the 3DTimon commercial software, and the other being a more advanced flow model implemented in more general fluid dynamics software. The focus will be on comparing the resulting fibre orientations.

  • 9.
    Alnersson, Gustaf
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Gestamp Hardtech, Luleå, Sweden.
    Ljung, Anna-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Fibre Orientation and Flow Modelling for Compression Moulding of SMC2022Inngår i: Svenska Mekanikdagar 2022 / [ed] Pär Jonsén; Lars-Göran Westerberg; Simon Larsson; Erik Olsson, Luleå tekniska universitet, 2022Konferansepaper (Fagfellevurdert)
  • 10.
    Alnersson, Gustaf
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Gestamp Hardtech, Luleå, Sweden.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Ljung, Anna-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Numerical Study of the 3D-Flow Characteristics During Compression Moulding of SMC2019Inngår i: Proceedings of the 2019 International Conference on Composite Materials: Melbourne, Australia, August 11-16, 2019 / [ed] Adrian Mouritz; Chun Wang; Bronwyn Fox, RMIT University , 2019, s. 1571-1581, artikkel-id 305Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    A numerical model for compression moulding of Sheet Moulding Compound is presented. The model is based on fluid mechanics and the SMC charge is modelled as a fluid with a viscosity that is dependent on the charge temperature, the fibre volume fraction of the material and the shear strain rate. Trends observed in the simulations regarding the shape of the flow front agree with experimental observations in previous studies. The simulations also yield that the type and magnitude of initial heating effects the initial flow to a large extent.

  • 11.
    Alnersson, Gustaf
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Gestamp Hardtech, Sweden.
    Tahir, M. Waseem
    Gestamp Hardtech, Sweden. Mechanical Engineering, University of Hull, UK.
    Ljung, Anna-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Review of the Numerical Modeling of Compression Molding of Sheet Molding Compound2020Inngår i: Processes, ISSN 2227-9717, Vol. 8, nr 2, artikkel-id 179Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    A review of the numerical modeling of the compression molding of the sheet molding compound (SMC) is presented. The focus of this review is the practical difficulties of modeling cases with high fiber content, an area in which there is relatively little documented work. In these cases, the prediction of the flows become intricate due to several reasons, mainly the complex rheology of the compound and large temperature gradients, but also the orientation of fibers and the micromechanics of the interactions between the fluid and the fibers play major roles. The details of this during moldings are discussed. Special attention is given to the impact on viscosity from the high fiber volume fraction, and the various models for this. One additional area of interest is the modeling of the fiber orientation.

  • 12.
    Altorkmany, Lobna
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    Kharseh, Mohamad
    Civil Environmental Engineering Department, Chalmers University of Technology, Sweden.
    Ljung, Anna-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Effect of Working Parameters of the Plate Heat Exchanger on the Thermal Performance of the Anti-Bact Heat Exchanger System to Disinfect Legionella in Hot Water Systems2018Inngår i: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 141, s. 435-443Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The objective of the current study is to analyze the effect of different working parameters on the thermal performance of the Anti-Bact Heat Exchanger system (ABHE). The ABHE system is inspired by nature and implemented to achieve continuous disinfection of Legionella in different human-made water systems at any desired disinfection temperature. In the ABHE system, most of the energy is recovered using an efficient plate heat exchanger (PHE). A model by Engineering Equation Solver (EES) is set-up to figure out the effect of different working parameters on the thermal performance of the ABHE system. The study shows that higher supplied water temperature can enhance the regeneration ratio (RR), but it requires a large PHE area and pumping power (PP) which consequently increase the cost of the ABHE system. However, elevate temperature in use results in a reduced PHE area and PP, which accordingly reduce the cost of the ABHE system. On the other hand, the EES-based model is used to study the effect of the length and the width of the plates used in the PHE on the RR and the required area of the PHE. Finally, taking into account the geometrical parameters, flow arrangement and the initial operating conditions of the PHE, the EES-based model is used to optimize the PHE in which its area is minimized, and the RR of the ABHE system is maximized.

  • 13.
    Altorkmany, Lobna
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    Kharseh, Mohamad
    Civil Environmental Engineering Department, Chalmers University of Technology.
    Ljung, Anna-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Experimental and Simulation Validation of ABHE for Disinfection of Legionella in Hot Water Systems2017Inngår i: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 116, s. 253-265Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The work refers to an innovative system inspired by nature that mimics the thermoregulation system that exists in animals. This method, which is called Anti Bacteria Heat Exchanger (ABHE), is proposed to achieve continuous thermal disinfection of bacteria in hot water systems with high energy efficiency. In particular, this study aims to demonstrate the opportunity to gain energy by means of recovering heat over a plate heat exchanger. Firstly, the thermodynamics of the ABHE is clarified to define the ABHE specification. Secondly, a first prototype of an ABHE is built with a specific configuration based on simplicity regarding design and construction. Thirdly, an experimental test is carried out. Finally, a computer model is built to simulate the ABHE system and the experimental data is used to validate the model. The experimental results indicate that the performance of the ABHE system is strongly dependent on the flow rate, while the supplied temperature has less effect. Experimental and simulation data show a large potential for saving energy of this thermal disinfection method by recovering heat. To exemplify, when supplying water at a flow rate of 5 kg/min and at a temperature of 50 °C, the heat recovery is about 1.5 kW while the required pumping power is 1 W. This means that the pressure drop is very small compared to the energy recovered and consequently high saving in total cost is promising.

    Fulltekst (pdf)
    fulltext
  • 14.
    Amiri, Kaveh
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    An experimental investigation of flow in a Kaplan runner: steady-state and transient2014Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Water turbines are since some years widely used for grid stabilization purposes according to their exceptional load variation capability which gives them the ability to compensate grid fluctuations initiated by the customer’s consumption or intermittent electricity production systems such as wind and solar power. Different renewable power generation technologies can be combined in mini-grids to electrify isolated villages and extend existing grid networks. In these occasions, small hydro units are also a good option to reduce the overall variability of supply to low levels and provide low‑cost, local electrification solutions. Hence, initially designed hydropower turbines for steady operation at on-design operating condition experience many off-design, start/stop and load variations during their life time according to the nowadays on-demand energy market and introduction of intermittent power generation systems to the electricity market.Start/stop and load variations can be harsh for the turbines due to the time dependent forces exerted on different parts of the turbines, especially rotating parts. Off-design performance of hydropower systems may also result in unfavorable and harmful periodic forces on the rotating parts. Therefore, investigations are required to study these working conditions and consider them in design of new hydropower plants and refurbished turbines. This was the motivation for the experimental investigation of a Kaplan turbine during on-design, off-design and transient operations with focus on the turbine’s rotor. The test case was a 1:3.1 scaled model of Porjus U9; a Kaplan turbine. The first paper deals with pressure measurements on the runner blades of the model under steady state operating conditions to find and quantify the sources of pressure fluctuations exerted on the runner at different operating points. The goal was to investigate the turbine’s performance at the best efficiency point with concentration on the performance of the water supply system and compare it to operations at high load and part load for a constant blades angle. The model results are compared with prototype measurements to corroborate the findings. The second paper presents the model investigations during load acceptance and load rejection. The model was investigated with pressure measurement on the stationary and rotating parts of the turbine under different load variations between part load, high load and best efficiency point. The third paper focuses on velocity measurements in the runner blade channels and at the runner outlet under on-design and off-design operating conditions. The velocity measurements are performed with a laser Doppler anemometry (LDA) system. The results of the model investigations along two propeller curves are presented to investigate the runner blade angle effects on the turbine’s performance.

    Fulltekst (pdf)
    FULLTEXT01
  • 15.
    Amiri, Kaveh
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Experimental investigation of a Kaplan runner under steady-state and transient operations2016Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Hydropower is a key part in electricity production nowadays. Hydropower electricity production rose to 3579.5 TWh in 2013, ranked as the second source of electricity production in the world after fossil fuels. It is the principle source of renewable electricity production, producing 16.2% of the electricity in 2013, accounting for 78% of the renewable electricity production in the world. Specifically in Sweden, hydropower is the main source of electricity production producing 47.5% of the required electricity. Nuclear, biomass, and wind placed in the following positions in the ranking in 2013 with 38.4%, 6.5%, and 4.3%, respectively.Besides meeting electricity demand with an environmental-friendly method, hydropower has a unique and important role which is grid regulation: balancing electricity production and consumption. Gas turbines and hydraulic turbines called “Primary reserves” are the only electricity production systems that can be used for fast regulations due to their short start-up time from 1 to 60 s. The obvious environmental problems, air pollution, and costs associated with gas turbines make hydropower a prime alternative whenever applicable. In Sweden, the share of fossil fuels in electricity production is small; 2.8% in 2012 with an average annual growth of -0.7% in the period 2002-2012. Hence, hydropower is practically the only available source used to regulate the grid fluctuations resulting from deregulated market and fast growth of intermittent power generation systems, i.e., solar and wind energy. Hydraulic turbines are subject to frequent off-design and transient operations because of their grid regulation responsibility. Such operating conditions decrease turbine’s efficiency and affect its lifetime significantly. Off-design and transient operation of hydraulic turbines may induce unpredicted pressure fluctuations on the stationary and rotating parts of the turbine. Special attention should be dedicated to the effects of such phenomena on the runner blades because of their importance on the efficiency of the turbine, and their vulnerability to the pressure fluctuations.This thesis presents an experimental investigation on the effects of off-design and transient operation of an axial hydraulic turbine on velocity fields and pressure fluctuations exerted on the runner and the draft tube of a turbine. The investigation was performed on a 1:3.1 scaled model of a Kaplan turbine known as Porjus U9. The main objective was to investigate the effect of operating point on pressure and velocity fluctuations in the runner and the draft tube. Another objective was to study the effect of transient operation on pressure fluctuations exerted on the runner and the draft tube, to investigate the formation and mitigation process of a rotating vortex rope (RVR) within the draft tube. Finally, the effect of the swirl leaving the runner and the draft tube bend on the performance of the turbine was investigated. The study involves pressure measurements on the runner blades and draft tube walls of the turbine, laser Doppler anemometry (LDA) measurements within and after the runner, and particle image velocimetry (PIV) measurements within the draft tube.The pressure and LDA results acquired during steady state operation of the turbine showed different sources of fluctuations on the runner at different operating points resulting in symmetric and asymmetric fluctuating forces on the runner. The pressure measurements during transient operating conditions exhibited pressure fluctuations exerted on the runner during load variations and elucidated some aspects of formation and mitigation process of RVR within the draft tube. The PIV measurements performed after the draft tube bend of the turbine focuses on the physical phenomena resulting in flow asymmetry after the draft tube bend of hydraulic turbines affecting their efficiency.

    Fulltekst (pdf)
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  • 16.
    Amiri, Kaveh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Department of Energy and Process Engineering, Water Power Laboratory, Norwegian University of Science and Technology, Trondheim, Norway.
    Mulu, Berhanu
    Vattenfall Research and Development, Älvkarleby, Sweden.
    Experimental investigation of the hydraulic loads on the runner of a Kaplan turbine model and the corresponding prototype2015Inngår i: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 53, nr 4, s. 452-465Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper reports on unsteady pressure measurements on the runner blades of a Kaplan turbine model as well as torque and radial load bearing measurements on the corresponding prototype at several operating points to investigate the sources of periodic loads exerted on the runner when operating at the best efficiency point and off design. Pressure measurements on the model runner blades indicated that the spiral casing delivers a poorly conditioned flow to the guide vanes close to the lip-entrance junction, resulting in flow separation on the guide vanes. The asymmetric flow delivered to the runner induces large oscillations with respect to the guide vane passing frequency, runner frequency and its harmonics to the runner blades. The torque measurements on the prototype also revealed an asymmetric flow at the distributor outlet. The bearing radial load measurements performed on the prototype support the torque measurement results. The asymmetric hydraulic loads on the runner result in shaft wobbling, and the oscillatory forces exerted on the blades are transferred to the main shaft and bearings. Another source of oscillating forces exerted on the runner blades is the rotating vortex rope (RVR) formation that occurs at part-load operation of the turbine and induces pressure fluctuations at two sub-synchronous frequencies to the runner.

  • 17.
    Amiri, Kaveh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Mulu, Berhanu
    Vattenfall Research & Development.
    Raisee, Mehrdad
    Mechanical Engineering Department, University of Tehran.
    Experimental study of fluid structure interaction in a Kaplan turbine runner blade2013Konferansepaper (Fagfellevurdert)
    Fulltekst (pdf)
    FULLTEXT01
  • 18.
    Amiri, Kaveh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Raisee, M.
    School of Mechanical Engineering, University of Tehran.
    Effects of flow unsteadiness on the wall shear stress2012Inngår i: 26th IAHR Symposium on Hydraulic Machinery and Systems: 19–23 August 2012, Beijing, China, IOP Publishing Ltd , 2012, s. 62033-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Measurements were performed on pulsating fully turbulent flows in a pipe test rig with a diameter of 100 mm. Sinusoidal oscillatory flow at different frequencies was superimposed on a mean flow of averaged Reynolds number Re=20000 based on the pipe diameter. The measurements have been performed at different forcing frequencies (0.001 < ω+ < 0.08) covering all the oscillatory regimes; quasi-steady, relaxation, quasi laminar and high frequency. The amplitude of the flow oscillation was small enough to allow a linear response in the measurements, i.e., all flow parameters showed an oscillatory behavior at the frequency of the flow. The amplitude of the oscillatory flow was about 10% of the mean velocity in all cases. The results include mean and phase averaged values of different parameters. The centerline velocity was measured by a 2D LDA system. Hot film and constant temperature anemometry system was used to determine the wall shear stress. Bulk velocity and pressure gradient along the pipe were also acquired. The results showed a good agreement with the previous analytical, experimental and numerical results available in the literature.

  • 19.
    Amiri, Kaveh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Mulu, Berhanu
    Vattenfall Research and Development, Älvkarleby.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Experimental Investigation of the Interblade Flow in a Kaplan Runner at Several Operating Points Using Laser Doppler Anemometry2016Inngår i: Journal of Fluids Engineering, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 138, nr 2, artikkel-id 21106Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents laser Doppler anemometry (LDA) measurements within the runner blade channels and at the runner outlet of a Kaplan turbine model. The model was investigated at six operating points located on two propeller curves of the turbine to study the flow condition during on-cam and off-cam operations. Main and secondary flows within and after the runner were analyzed, and the effects of the hub and tip clearances on the velocity fields within and after the runner were evaluated. Operation of the turbine at flow rates that are lower than the designed rate for the corresponding propeller curve resulted in vortex breakdown and the formation of a rotating vortex rope (RVR). The RVR formation produced an asymmetrical velocity distribution within and after the runner. The results demonstrated the occurrence of an oscillating flow with the same frequency as the vortex rope within the blade channels located upstream of the RVR. This results in an asymmetric flow through the runner and oscillating forces on the runner blades. The measured velocities indicated that the geometrical asymmetries in the runner manufacturing process resulted in various flow asymmetries at the measured sections. The asymmetries were up to 3% within the runner and 7% at the runner outlet

  • 20.
    Amiri, Kaveh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Mulu, Berhanu
    Vattenfall Research and Development, Älvkarleby, 814 70, Sweden.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Department of Energy and Process Engineering, Water Power Laboratory, Norwegian University of Science and Technology, Trondheim, 7491, Norway.
    Raisee, Mehrdad
    Mechanical Engineering Department, University of Tehran, 14155-6448, Tehran, Iran.
    Effects of load variation on a Kaplan turbine runner2016Inngår i: The International Journal of Fluid Machinery and Systems, E-ISSN 1882-9554, Vol. 9, nr 2, s. 182-193Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Introduction of intermittent electricity production systems like wind and solar power to electricity market together with the deregulation of electricity markets resulted in numerous start/stops, load variations and off-design operation of water turbines. Hydraulic turbines suffer from the varying loads exerted on their stationary and rotating parts during load variations they are not designed for such operating conditions. Investigations on part load operation of single regulated turbines, i.e., Francis and propeller, proved the formation of a rotating vortex rope (RVR) in the draft tube. The RVR induces pressure pulsations in the axial and rotating direction called plunging and rotating modes, respectively. This results in oscillating forces with two different frequencies on the runner blades, bearings and other rotating parts of the turbine. This study investigates the effect of transient operations on the pressure fluctuations exerted on the runner and mechanism of the RVR formation/mitigation. Draft tube and runner blades of the Porjus U9 model, a Kaplan turbine, were equipped with pressure sensors for this purpose. The model was run in off-cam mode during different load variations. The results showed that the transients between the best efficiency point and the high load occurs in a smooth way. However, during transitions to the part load a RVR forms in the draft tube which induces high level of fluctuations with two frequencies on the runner; plunging and rotating mode. Formation of the RVR during the load rejections coincides with sudden pressure change on the runner while its mitigation occurs in a smooth way.

  • 21.
    Amiri, Kaveh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Mulu, Berhanu G.
    Vattenfall Research and Development, Älvkarleby.
    Raisee, Mehrdad
    Mechanical Engineering Department, University of Tehran.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Effects of upstream flow conditions on runner pressure fluctuations2017Inngår i: Journal of Applied Fluid Mechanics, ISSN 1735-3572, E-ISSN 1735-3645, Vol. 10, nr 4, s. 1045-1059Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The rotor-stator interaction and the corresponding pressure fluctuations represent one of the sources of pressure and load fluctuations on the rotating parts of rotating machineries. The high-Reynolds flow is subject to rotation in the comparably large vaneless space of axial turbines, causing wake interaction and wake dissipation in this region. This increases the level of flow complexity in this region. This study examined the effect of the flow condition entering the spiral casing on the flow condition within the distributor and the runner and the physical source of pressure fluctuations exerted on the runner of a Kaplan turbine model. Simulations were performed within the water supply system, including the upstream tank, penstock, and the Francis turbines, the level of entering the spiral casing; the results were compared with laser Doppler anemometry (LDA) results. The results were considered as the inlet boundary condition for simulation of the turbine model from the spiral inlet to the draft tube outlet to investigate the flow condition within the distributor and the runner. The CFD simulations showed that the water supply system induces inhomogeneity to the velocity distribution at the spiral inlet. However, the flow condition does not affect the pressure fluctuations exerted on the runner blades due to the rotor-stator interactions. Moreover, the dominant frequencies exerted on the runner blades were accurately approximated although the amplitudes of the fluctuations were underestimated.

  • 22.
    Amiri, Kaveh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Mulu, Berhanu
    Vattenfall AB, Älvkarleby, Sweden.
    Raisee, Mehrdad
    School of Mechanical Engineering, College of Engineering, University of Tehran, P.O. Box: 11155-4563, Tehran, Iran.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Department of Energy and Process Engineering, Water Power Laboratory, Norwegian University of Science and Technology, Trondheim, Norway.
    Experimental study on flow asymmetry after the draft tube bend of a Kaplan turbine2016Inngår i: Advances and Applications in Fluid Mechanics, ISSN 0973-4686, Vol. 19, nr 2, s. 441-472Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Flow condition in a Kaplan turbine draft tube is investigated using laser Doppler anemometry (LDA) and particle image velocimetry(PIV). The investigated draft tube is composed of a cone followed by an elbow and a straight diffuser. The three velocity components were measured after the elbow at two different locations across the straight diffuser to quantify the flow asymmetry as well as the secondary flows formed in this region. The velocity profiles at the draft tube inlet are measured using a 2D LDA system allowing estimation of the draft tube inlet swirl. The results are presented at three operating points of the turbine. The flow condition after the draft tube bend was shown to be highly dependent on the vortex structures within the straight draft tube; namely Dean vortices and the swirl leaving the runner. At operating points with high flow rates and low swirl, Dean vortices dominate the upstream swirl; a symmetric but inhomogeneous flow resembling flow after a pipe bend forms within the straight diffuser. At part load operating points with high swirl and low flow rate, the flow after the bend is dominated by the upstream swirl resulting in asymmetric flow after the draft tube bend. The flow asymmetry is shown to be a 2nd order function of the swirl-to-Dean ratio.

  • 23.
    Amiri, Kaveh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Mulu, Berhanu
    Vattenfall Research & Development.
    Raisee, Mehrdad
    School of Mechanical Engineering, University of Tehran, Mechanical Engineering Department, University of Tehran.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Load variation effects on the pressure fluctuations exerted on a Kaplan turbine runner2014Inngår i: 27th IAHR Symposium on Hydraulic Machinery and Systems, IAHR 2014: Montreal, Canada, 22- 26 September 2014 / [ed] A-M Giroux, IOP Publishing Ltd , 2014, artikkel-id 32005Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Introduction of intermittent electricity production systems like wind power and solar systems to electricity market together with the consumption-based electricity production resulted in numerous start/stops, load variations and off-design operation of water turbines. The hydropower systems suffer from the varying loads exerted on the stationary and rotating parts of the turbines during load variations which they are not designed for. On the other hand, investigations on part load operation of single regulated turbines, i.e., Francis and propeller, proved the formation of rotating vortex rope (RVR) in the draft tube. The RVR induces oscillating flow both in plunging and rotating modes which results in oscillating force with two different frequencies on the runner blades, bearings and other rotating parts of the turbine. The purpose of this study is to investigate the effect of transient operations on the pressure fluctuations on the runner and mechanism of the RVR formation/mitigation. Draft tube and runner blades of the Porjus U9 model, a Kaplan turbine, were equipped with pressure sensors. The model was run in off-cam mode during different load variation conditions to check the runner performance under unsteady condition. The results showed that the transients between the best efficiency point and the high load happens in a smooth way while transitions to/from the part load, where rotating vortex rope (RVR) forms in the draft tube induces high level of fluctuations with two frequencies on the runner; plunging and rotating mode of the RVR.

  • 24.
    Amiri, Kaveh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Mulu, Berhanu
    Vattenfall Research and Development, Älvkarleby.
    Raisee, Mehrdad
    School of Mechanical Engineering, University of Tehran, Mechanical Engineering Department, University of Tehran.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Unsteady pressure measurements on the runner of a Kaplan turbine during load acceptance and load rejection2016Inngår i: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 54, nr 1, s. 56-73Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper addresses unsteady pressure measurements on the blades and stationary parts of a Kaplan turbine model (Porjus U9) during load variation. The turbine was studied in various load acceptance and load rejection scenarios in off-cam mode to investigate the effect of the transients on the turbine performance. The formation and mitigation processes for the rotating vortex ropes and their effects on the forces exerted on the runner were also investigated. The results show a smooth transition during load variations between high load and the best efficiency point, at which no rotating vortex ropes form in the draft tube. However, load variation to part load resulted in a draft tube surge and the formation of a rotating vortex rope with two fluctuating components: rotating and plunging. The rotating vortex ropes began to form at the end of the draft tube cone during the closure of the guide vanes and travelled upstream with further guide vane closure. The plunging mode induced flow oscillation throughout the entire turbine conduit, whereas the rotating mode resulted in local pressure fluctuations. The rotating vortex ropes induced wide-band pressure fluctuations on the suction side of the runner close to the hub section. The formation of the rotating vortex ropes near the runner resulted in a sudden change in the pressure exerted on the suction side of the blades, whereas the rotating vortex rope mitigation process proceeded in a smooth manner.

  • 25.
    Amiri, Kaveh
    et al.
    Department of Aerospace, Sharif University of Technology, Tehran, Iran.
    Soltani, Mohammad Reza
    Department of Aerospace, Sharif University of Technology, Tehran, Iran.
    Haghiri, Ali
    Amirkabir University of Technology, Tehran, Iran.
    Steady flow quality assessment of a modified transonic wind tunnel2013Inngår i: Scientia Iranica, ISSN 1026-3098, Vol. 20, nr 3, s. 500-507Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An existing operational trisonic wind tunnel is upgraded to improve its performance criterion in the transonic regime. In this research, the test section is modified according to the operational requirements of the various existing transonic wind tunnels. Several perforated walls are designed, manufactured, and installed on the top and bottom sides of the test section. The flow in the test section of the wind tunnel is surveyed for the empty condition prior to testing models. Once satisfactory results regarding the flow quality requirements in the test section under various conditions were achieved, a 2D model, NACA 0012, and a 3D standard model for the transonic wind tunnels, AGARD-B, are manufactured and tested under various conditions for the purpose of integral calibration and validation of the tunnel data. Surface pressure distribution as well as the force and moment data compare well with the existing data from other tunnels for similar models tested under the same conditions.

  • 26.
    Andersson, Anders G.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Modelling flow with free and rough surfaces in the vicinity of hydropower plants2013Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Flow with free and rough surfaces near hydropower stations is of interest for both engineering and environmental applications. Here, Computational Fluid Dynamics simulations of free surface flow and flow over rough surfaces in regulated rivers were performed in applications such fish migration, spillway design and flow over rough surfaces as in hydropower tunnels or natural channels. For all the investigated applications it is typical with very large geometrical scales, high flow rates and highly turbulent flow. Modelling boundaries such as free water surfaces and rough walls presents a challenge and was given special attention as well as the treatment of turbulence. Validation of the numerical simulations was performed in all cases with methods such as acoustic measurements with an Acoustic Doppler Current Profiler (ADCP), Acoustic Doppler Velocimeter (ADV) and optical measurements with Particle Image Velocimetry (PIV).Numerical simulations have been used to evaluate the flow downstream the Stornorrfors hydropower plant in Umeälven with regards to upstream migrating fish. Field measurements with an ADCP were performed and the measurements were used to validate the simulations. By adding a fish ladder in the simulations it was possible to investigate the attraction water created from the fishway at different positions and angles. An additional possibility to create better attraction water and improve the conditions for upstream migrating fish was simulated by guiding the spill water from the hydropower dam through a smaller passage from the old river bed.Fish population data from the same location was compared with flow fields from numerical simulations. The population data was compared with variables such as velocity, vorticity and turbulence intensity. A correlation between fish detections and turbulence intensity was shown.Simulations on the spilling from a dam were performed and compared to experimental results from a physical scale model. ADV was used to measure the velocity and validate the simulations. Two different spillway configurations were considered and simulations with both the Rigid Lid model and the Volume of Fluids method were carried out. Water levels, velocities and the shape of the water surface were compared between simulations and experiments. The simulations capture both qualitative features such as a vortex near the outlet and show good quantitative agreement with the experiments.A wall with large surface roughness was created by laser scanning a tunnel. One of the side walls was down-scaled and used to create a rough wall in a channel with rectangular cross-section for both a numerical model and an experimental model. Numerical simulations were performed and validated by PIV-measurements in the experimental model.The resolution of the geometry for the rough surface was lowered in two steps and numerical simulations were performed for flow over all three surfaces. The difference in flow fields in the bulk and near wall region was investigated as well as the difference in turbulent quantities which can provide good input for a new model for surface roughness in applications with very large surface roughness and high velocities such as flow in hydropower tunnels or natural channels and rivers.

    Fulltekst (pdf)
    FULLTEXT01
  • 27.
    Andersson, Anders G.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Simulations and measurements of free surface flow in regulated rivers2010Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Open channel flow near hydropower stations is of interest for both engineering and environmental applications. In this research project Computational Fluid Dynamics simulations of free surface flow in regulated rivers were applied with both fish migration and validation of numerical simulations in focus. In the first paper, numerical simulations has been used to evaluate the flow downstream a hydropower plant with regards to upstream migrating fish. Field measurements with an Acoustic Doppler Current Profiler were performed and the measurements were used to validate the simulations. In the second paper ,simulations on the spilling from a dam were performed and compared to experimental results from a physical scale model. The third paper deals with more in depth analysis of field measurements where the variations in the flow downstream a hydropower plant was examined.

    Fulltekst (pdf)
    FULLTEXT01
  • 28.
    Andersson, Anders G.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Andreasson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Modelling and validation of flow over a wall with large surface roughness2012Konferansepaper (Fagfellevurdert)
    Fulltekst (pdf)
    FULLTEXT01
  • 29.
    Andersson, Anders G.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Andreasson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    CFD-modelling and validation of free surface flow during spilling of reservoir in down-scale model2013Inngår i: Engineering Applications of Computational Fluid Mechanics, ISSN 1994-2060, E-ISSN 1997-003X, Vol. 7, nr 1, s. 159-167Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fully three dimensional modelling of the spilling from a reservoir with relatively complex geometry were performed and compared to experimental results from a physical scale model with the aim to advance the science of numerical modelling of free surface flow of real reservoirs. In the set-up in focus the water was spilled from the reservoir through three gates that could be manoeuvred separately. In the first case two of the gates were closed and the third gate was partly opened. In this experimental set-up the water surface in the reservoir was close to horizontal. Therefore it was here meaningful to compare a rigid lid modelling approximation to the more computational heavy method of Volume of Fluids. In the second case, all three gates were open, resulting in a nonhorizontal varied flow surface profile in the reservoir upstream critical sections at the spillway crests. This case was simulated with Volume of Fluids and the position of the air-water interface was derived for two turbulence models, the standard k-ε and SSG. Water levels, velocities and the shape of the water surface were compared to experiments. The simulation results capture qualitative features such as a vortex near the outlet and show good quantitative agreement with the experiments regardless of method used to simulate the free surface. In general, simulations with the standard k-ε and the more advanced SSG turbulence models give the same results with respect to the averaged quantities measured.

  • 30.
    Andersson, Anders G.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Andreasson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Modellering av avbördning med fri vattenyta och validering i en skalmodell2011Konferansepaper (Fagfellevurdert)
    Fulltekst (pdf)
    FULLTEXT01
  • 31.
    Andersson, Anders G.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Andreasson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Effect of spatial resolution of rough surfaces on numerically computed flow fields with application to hydraulic engineering2014Inngår i: Engineering Applications of Computational Fluid Mechanics, ISSN 1994-2060, E-ISSN 1997-003X, Vol. 8, nr 3, s. 373-381Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In numerical simulations of flow over rough surfaces, the roughness is often not resolved but represented by a numerical model. The validity of such an assumption is investigated in this paper by Reynolds-Averaged Navier-Stokes simulations of flow over a surface with a large roughness. The surface was created from a high-resolution laser scanning of a real rock blasted tunnel. By reducing the geometrical resolution of the roughness in two steps, the importance of an appropriate surface description could be examined. The flow fields obtained were compared to a set-up with a geometrical flat surface where the roughness was represented by a modified form of the Launder and Spalding wall-function. The flow field over the surface with the lowest resolution was substantially different from those of the two finer resolutions and rather close to the results from the set-up with the wall-function. The results also yield that the finer the resolution is the more vorticity is formed close to the rough surface and more turbulence is generated.

  • 32. Andersson, Anders G.
    et al.
    Lindberg, Dan-Erik
    Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
    Lindmark, Elianne
    Leonardsson, Kjell
    Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
    Andreasson, Patrik
    Lundqvist, Hans
    Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    A numerical study of the location and function of the entrance of a fishway in a regulated river2010Inngår i: 8th International Symposium on ECOHYDRAULICS: Bridging between Ecology and Hydraulics and Leading the Society's New Need - Living with Nature, 2010, s. 277-284Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Simulation driven design with Computational Fluid Dynamics has been used to evaluate the flow downstream a hydropower plant with regards to upstream migrating fish. Field measurements with an Acoustic Doppler Current Profiler were performed and the measurements were used to validate the simulations. The measurements indicate a more unstable flow than the simulations and the tailrace jet from the turbines is stronger in the simulations. The simulations are however considered to capture the important features of the flow in a way that makes them viable for attraction water simulations. A fishway entrance was included in the simulations and the subsequent attraction water was evaluated for two positions and two angles of the entrance at different turbine discharges. Results show that both positions are viable and that a position where the flow from the fishway does not have to compete with the flow from the power plant will generate superior attraction water. Simulations were also performed further downstream where the flow from the turbines meets the old river bed which is the current fish passage for upstream migrating fish. A modification of the old river bed was made in the model as one scenario to generate better attraction water. This considerably increases the attraction water although it cannot compete with the flow from the tailrace tunnel.

    Fulltekst (pdf)
    FULLTEXT01
  • 33.
    Andersson, Anders G.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lindberg, Dan-Erik
    SLU.
    Lindmark, Elianne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Leonardsson, Kjell
    SLU.
    Andreasson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundqvist, Hans
    SLU.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    A study of the location of the entrance of a fishway in a regulated river with CFD and ADCP2012Inngår i: Modelling and Simulation in Engineering, ISSN 1687-5591, E-ISSN 1687-5605, Vol. 2012, artikkel-id 327929Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Simulation-driven design with computational fluid dynamics has been used to evaluate the flow downstream of a hydropower plant with regards to upstream migrating fish. Field measurements with an Acoustic Doppler Current Profiler were performed, and the measurements were used to validate the simulations. The measurements indicate a more unstable flow than the simulations, and the tailrace jet from the turbines is stronger in the simulations. A fishway entrance was included in the simulations, and the subsequent attraction water was evaluated for two positions and two angles of the entrance at different turbine discharges. Results show that both positions are viable and that a position where the flow from the fishway does not have to compete with the flow from the power plant will generate superior attraction water. Simulations were also performed for further downstream where the flow from the turbines meets the old river bed which is the current fish passage for upstream migrating fish. A modification of the old river bed was made in the model as one scenario to generate better attraction water. This considerably increases the attraction water although it cannot compete with the flow from the tailrace tunnel.

    Fulltekst (pdf)
    fulltext
  • 34. Andersson, Anders G.
    et al.
    Lindmark, Elianne
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    CFD-modell av turbinutloppet i Stornorrfors2009Inngår i: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, s. 106-Konferansepaper (Annet vitenskapelig)
  • 35.
    Andersson, Anders G.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Kristoffer
    Andreasson, Patrik
    Lundström, Staffan
    Simulation of free surface flow in a spillway with the rigid lid and volume of fluid methods and validation in a scale model2010Inngår i: Proceedings, Fifth European Conference on Computational Fluid Dynamics / [ed] Jose C. F. Pereira; Adelia Sequeira; Jose M. C. Pereira, 2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Simulations on the spilling from a dam were performed and compared to experimental results from a physical scale model. Both mechanical and acoustic methods to measure the velocity were used. The model has three gates leading into the spillway that can be maneuvered separately. At first two of the gates were closed and the inlet flow was high enough to get a fully wetted outlet at the third gate. This case was simulated with a rigid lid approximation since the water surface was considered to be plane. The water surface level was taken from the scale model. In the second case, all three gates were open resulting in a free water surface through all the gates to the spillway. This case was simulated with the Volume of Fluids method were both water and air phase were considered. Water levels, velocities and the shape of the water surface were compared between simulations and experiments. The simulations capture both qualitative features such as a vortex near the outlet and show good quantitative agreement with the experiments.

    Fulltekst (pdf)
    FULLTEXT01
  • 36.
    Andersson, Anders G.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lycksam, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hydraulic Modelling of a Regulated River Reach on Different Scales to Evaluate its Inherent Environmental Conditions2022Inngår i: Proceedings of the 39th IAHR World Congress: From Snow To Sea / [ed] Miguel Ortega-Sánchez, International Association for Hydro-Environment Engineering and Research (IAHR) , 2022, s. 4189-4195Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Hydraulic modelling can be an important tool to assess ecological status of rivers and to evaluate where and how measures should be implemented to maximize their impact. This is becoming increasingly important in regulated rivers since hydropower’s ability to balance intermittent electricity sources such as wind- and solar power is resulting in more frequent starts and stops of the power plants, which in turn is affecting the local environmental conditions. The resulting flow fields from the modelling can, for instance, be used to classify biologically important areas in rivers. Several relevant flow parameters can be predicted and applied, e.g., depth and water velocities can be used to estimate habitat for specific fish species or the variation in water levels can be used to evaluate the risk of stranding for fish in different life stages. This work specifically involves numerical modelling of a heavily regulated reach in the Lule River in northern Sweden. Models are created in 1D, 2D and 3D to show strengths and weaknesses in the different modelling techniques. To ensure that the models capture reality, measurements of water levels and temperatures in the reach are performed using pressure/temperature loggers for validation purposes. River velocities are also measured with an Acoustic Doppler Current Profiler which are mainly used to validate the 3D model. The results derived using the different modelling methods are all shown to be useful depending on relevant application.

    Fulltekst (pdf)
    fulltext
  • 37.
    Andersson, Anders G.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Westerberg, Lars-Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Papathanasiou, T.D.
    Department of Mechanical Engineering, University of Thessaly, 38 334 Volos, Greece.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Flow through a two-scale porosity material2009Inngår i: Research Letters in Materials Science, ISSN 1687-6822, E-ISSN 1687-6830, artikkel-id 701512Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    Flow through a two-scale porous medium is here investigated by a unique comparison between simulations performed with computational fluid dynamics and the boundary element method with microparticle image velocimetry in model geometries.

    Fulltekst (pdf)
    fulltext
  • 38. Andersson, Anders G.
    et al.
    Westerberg, Lars-Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Papathanasiou, Thanasis
    Lundström, Staffan
    Fluid flow through porous media with dual scale porosity2008Inngår i: Proceedings of the 19th International Symposium on Transport Phenomena (ISTP-19): Reykjavik, Iceland, August 17-21, 2008 / [ed] Sigurdur Brynjolfsson; Olafur Petur Palsson; Jong H. Kim, University of Iceland, Faculty of Industrial Engineering, Mechanical Engineering and Computer Science , 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Flow in two scale porous media takes place in applications such as advanced composites manufacturing. Knowledge of this flow is of general importance and is crucial for filtration mechanisms when functional filler-particles are added to the liquid resin impregnating the fibrous preform. Means to model and experimentally visualise this flow is here investigated. In particular simulations performed with computational fluid dynamics and the boundary element method are compared to micro particle image velocimetry in a model geometry.

    Fulltekst (pdf)
    FULLTEXT01
  • 39.
    Andersson, Anders
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Leonardsson, Kjell
    Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
    Lindberg, Dan-Erik
    Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, Gunnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundqvist, Hans
    Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
    Describing fish passage in a river confluence with telemetry and CFD2016Inngår i: / [ed] Webb, JA, Costelloe, JF, CasasMulet, R, Lyon, JP, Stewardson, MJ, Melbourne: University of Melbourne , 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The confluence between hydropower tailrace and the old river bed in Stornorrfors in the river Umeälven in the northern part of Sweden has shown to be the largest obstacle for upstream migrating salmon and sea trout during the migrating season. Fish are attracted to the high flow rate from the tailrace and will not migrate upstream in the old river bed being the passage to the fishway leading past the hydropower dam. By triangulating the movements of radio tagged fish using eight antennas in the confluence, it is here possible to describe the individual fish tracks left by radio tagged fish during the migrating season. These tracks are then compared with three-dimensional Computational Fluid Dynamics (CFD) simulations of the confluence. By simulating the most common combinations of turbine flow and spill flow in the old river bed it is then possible to find correlations between individual fish movements and flow parameters such as velocity, turbulence intensity or vorticity for different flow combinations. It was previously assumed that fish had trouble locating the old river bed, the results of the triangulation however shows that most fish finds the old river bed within a few days but does not chose to migrate until several days (or weeks) later. The main issue to be solved is therefore not how to attract the fish to the old river bed but rather how to create favorable conditions in the old river bed so that migrating fish are more inclined to take that path upstream.

    Fulltekst (pdf)
    fulltext
  • 40.
    Andersson, Andreas
    et al.
    Electric Propulsion Systems Department, Volvo Car Group, Gothenburg, Sweden.
    Lennström, David
    oise, Vibrations, and Harshness Department, Volvo Car Group, SE-405 31 Gothenburg.
    Nykänen, Arne
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Influence of Inverter Modulation Strategy on Electric Drive Efficiency and Perceived Sound Quality2016Inngår i: IEEE Transactions on Transportation Electrification, ISSN 2332-7782, Vol. 2, nr 1, s. 24-35, artikkel-id 7370814Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents an evaluation of differentmodulation techniques and different levels of switching frequencyrandomization for a rear axle electrical drive unit used in auto-motive applications. Inverter and machine losses, and perceivedsound quality of high-frequency acoustic noise are investigated byfinite element calculations, experimental testing, and subjectivenoise assessment. Additionally, stator current harmonics, airgapflux density harmonics, and force density harmonics are comparedfor space vector modulation (SVM) and discontinuous pulsewidthmodulation through finite element modeling. The main conclusionis that, primarily in the field weakening region, significant energysavings can be achieved (up to 17% decrease in total inverter losseswith a switching frequency of 10 kHz). This is obtained withoutdeterioration of perceived sound quality by the use of discontinu-ous pulsewidth modulation with switching frequency randomiza-tion. Furthermore, randomization of the switching frequency doesnot improve the perceived sound quality of the acoustic noise whenusing SVM. However, for discontinuous pulsewidth modulation,improvements in perceived sound quality when randomizing theswitching frequency are observed, primarily below base speed.

  • 41.
    Andersson, H.M.
    et al.
    Luleå tekniska universitet.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gebart, B. Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Synnergren, Per
    Luleå tekniska universitet.
    Application of digital speckle photography to measure thickness variations in the vacuum infusion process2003Inngår i: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 24, nr 3, s. 448-455Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new method to measure the movement of the flexible bag used in vacuum infusion is presented. The method is based on an in-house developed stereoscopic digital speckle photography system (DSP). The advantage with this optical method, which is based on cross-correlation, is that the deflection of a large area can be continuously measured with a great accuracy (down to 10 μm. The method is at this stage most suited for research but can in the long run also be adopted in production control and optimization. By use of the method it was confirmed that a ditch is formed at the resin flow front and that there can be a considerable and seemingly perpetual compaction after complete filling. The existence of the ditch demonstrates that the stiffness of the reinforcement can be considerably reduced when it is wetted. Hence, the maximum fiber volume fraction can be larger than predicted from dry measurements of preform elasticity. It is likely that the overall thickness reduction after complete filling emanates from lubrication of the fibers combined with an outflow of the resin. Besides, the cross-linking starts and the polymer shrinks. Hence, the alteration in height will continue until complete cross-linking is reached.

  • 42.
    Andersson, L. Robin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    A Method for Decomposing Surface Roughness in Blasted Hydropower Waterways2022Inngår i: Svenska Mekanikdagar 2022 / [ed] Pär Jonsén; Lars-Göran Westerberg; Simon Larsson; Erik Olsson, Luleå tekniska universitet, 2022Konferansepaper (Fagfellevurdert)
    Fulltekst (pdf)
    fulltext
  • 43.
    Andersson, L. Robin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Andreasson, P.
    Vattenfall Research and Development AB, Älvkarleby, Sweden.
    In-situ Pressure Measurements in Gavunda HydropowerTunnel during Full Operation2022Inngår i: Proceedings of the 39th IAHR World Congress: From Snow To Sea / [ed] Miguel Ortega-Sánchez, International Association for Hydro-Environment Engineering and Research , 2022, s. 2875-2879Konferansepaper (Fagfellevurdert)
  • 44.
    Andersson, L. Robin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Andreasson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Vattenfall Research and Development AB, Älvkarleby, Sweden.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Estimating localized pressure fluctuations in Gävunda hydropower tunnel2020Inngår i: Proceedings of the 8th IAHR International Symposium on Hydraulic Structures ISHS2020, The University of Queensland , 2020Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A numerical investigation of a hydropower tunnel has been implemented in this project. The tunnel geometry data were taken from a laser scanning of a tunnel positioned in Gävunda, Sweden. While the average cross-section of the tunnel is even, in accordance with the pre-excavation schematics, the instantaneous deviations are significant. ANSYS-CFX was applied for the simulations using a RANS approach with k-ε model for turbulence closure. To evaluate the results, the pressure was area averaged in 30 planes evenly spaced perpendicular to the flow direction inside the tunnel. Additionally, the pressure was sampled along a line running from the inlet to the outlet of the tunnel. Results show that the area averaged pressure is similar to the pressure modelled along the center line. This means that the roughness has a dominating effect on the bulk flow inside of the tunnel. Hence, cross-sectional based methods of evaluation (e.g. Gauckler-Manning) could potentially be used to evaluate the localized pressure inside the tunnel. Further evaluation show that the Gauckler-Manning and Haaland equation both can be used as an estimate of the modelled pressure inside of the tunnel. Both equations are highly dependent on the hydraulic radius and cross-sectional area. These results have many implications, continuous pressure measurements can potentially be used to monitor the structural integrity of tunnels. Similarly, tunnel data could be used to estimate pressure effects within the tunnel, which would enable easier and reliable risk assessment studies.

  • 45.
    Andersson, L. Robin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Larsson, I. A. Sofia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Burman, Anton J.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Andreasson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Vattenfall Research and Development, Älvkarleby, Sweden.
    Localized roughness effects in non-uniform hydraulic waterways2021Inngår i: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 59, nr 1, s. 100-108Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydropower tunnels are generally subject to a degree of rock falls. Studies explaining this are scarce and the current industrial standards offer little insight. To simulate tunnel conditions, high Reynolds number flow inside a channel with a rectangular cross-section is investigated using Particle Image Velocimetry and pressure measurements. For validation, the flow is modelled using LES and a RANS approach with k - ε turbulence model. One wall of the channel has been replaced with a rough surface captured using laser scanning. The results indicate flow-roughness effects deviating from the standard non-asymmetric channel flow and hence, can not be properly predicted using spatially averaged relations. These effects manifest as localized bursts of velocity connected to individual roughness elements. The bursts are large enough to affect both temporally and spatially averaged quantities. Both turbulence models show satisfactory agreement for the overall flow behaviour, where LES also provided information for in-depth analysis.

  • 46.
    Andersson, L. Robin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Larsson, Sofia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Andreasson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Vattenfall Research and Development, Älvkarleby.
    Andersson, Anders G.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Characterization of Flow Structures Induced by Highly Rough Surface Using Particle Image Velocimetry, Proper Orthogonal Decomposition and Velocity Correlations2018Inngår i: Engineering, ISSN 1947-3931, Vol. 10, s. 399-416Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High Reynolds number flow inside a channel of rectangular cross section is examined using Particle Image Velocimetry. One wall of the channel has been replaced with a surface of a roughness representative to that of real hydropower tunnels, i.e. a random terrain with roughness dimensions typically in the range of ≈10% - 20% of the channels hydraulic radius. The rest of the channel walls can be considered smooth. The rough surface was captured from an existing blasted rock tunnel using high resolution laser scanning and scaled to 1:10. For quantification of the size of the largest flow structures, integral length scales are derived from the auto-correlation functions of the temporally averaged velocity. Additionally, Proper Orthogonal Decomposition (POD) and higher-order statistics are applied to the instantaneous snapshots of the velocity fluctuations. The results show a high spatial heterogeneity of the velocity and other flow characteristics in vicinity of the rough surface, putting outer similarity treatment into jeopardy. Roughness effects are not confined to the vicinity of the rough surface but can be seen in the outer flow throughout the channel, indicating a different behavior than postulated by Townsend’s similarity hypothesis. The effects on the flow structures vary depending on the shape and size of the roughness elements leading to a high spatial dependence of the flow above the rough surface. Hence, any spatial averaging, e.g. assuming a characteristic sand grain roughness factor, for determining local flow parameters becomes less applicable in this case.

  • 47. Andersson, Magnus
    Vacuum infusion of polymer composites2001Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The current trend towards an increased use of vacuum infusion for manufacturing of high performance fibre reinforced polymer composites has stressed the necessity of an advanced modelling of the process. Until recent years development in this area has mainly been based on trial and error and the behaviour of the method is therefore not fully understood. The basic principle of the vacuum infusion process is that a stack of dry fabrics is placed between a stiff mould half and a flexible and airtight bag. The bag is sealed to the mould expect at certain positions being open for resin supplies and outlets. Liquid resin then penetrates the stack by a reduction of the pressure at one or several positions in the formed cavity. After complete filling the pressure in the cavity is evened out by retaining the vacuum level at the outlets throughout curing of the resin. The overall goal of this research is to develop tools that ensure optimum and secure processing in practical work with vacuum infusion. The means to achieve this goal has so far been industry scale experiments, simple analysis and numerical simulations. The experimental part comprises full-scale impregnations where thickness variations are measured with an advanced optical metrology system and the out-of-plane flow front is monitored by means of colour marks in the reinforcement stack. Experimental findings are then incorporated in a numerical model including moving boundaries and two-phase flow through porous media based on a commercial software for computational fluid dynamics.

    Fulltekst (pdf)
    FULLTEXT01
  • 48. Andersson, Magnus
    Visualisation of composites manufacturing2003Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The five papers in this thesis demonstrate five unique ways to monitor composite manufacturing. They also clarify several phenomena that take place during composite manufacturing. Of particular interest are two manufacturing methods, namely vacuum infusion (Paper A-D) and compression moulding of SMC (Paper E). The former process is, for instance, used for large surface area parts such as wind-turbine blades. The concept is that a dry reinforcement is placed on a stiff mould half and covered with a flexible and airtight bag. The bag is then sealed to the mould except at certain positions being open for resin supplies and outlets. By keeping the pressure atmospheric at the resin inlets and reducing the pressure at one or several positions in the formed cavity, liquid resin is forced to impregnate the stack. A further result of the difference between the ambient pressure and the pressure within the cavity is a compaction force and a corresponding compression of the elastic stack. In compression moulding of SMC a charge consisting of a polymer, fillers and chopped fibres is placed in a heated and open mould. When the mould is closed, the charged material will fill the mould. This is a rapid process and it is therefore suitable for parts to the automotive industry. Exclusively, this thesis presents optical measurements of the full 3D position of the flow front during vacuum infusion moulding. Equally exceptional are field measurements made with a stereoscopic digital speckle photography system of the movement of the bag during moulding by the same manufacturing process. The actual results from these two measuring techniques are also very interesting. First of all is it clarified that there can be rather large gradients in the flow front with respect to the thickness direction enabling the formation of voids. Secondly it is shown that certain permeability measurements could be used to predict the flow front position during vacuum infusion while others fail. Thirdly it is confirmed that a ditch is formed at the resin flow front and that there can be a considerable and seemingly perpetual compaction after complete filling. Special attention has also been given to the advancing flow front during compression moulding of SMC. In this case the full complexity is captured by means of continuous high resolution close-up monitoring. From these visualisations three phases are defined, namely pitch, floating, and boiling. In the initial phase, pitch, outer layers do not remain outer layers, the actual flow is very complex and air is likely to be entrapped. In the second phase, floating, the flow is stable and seemingly viscous. In the last phase, boiling, bubbles are observed in the low pressure region at the flow front, favouring the formation of void both internally and on the surface. For vacuum infusion it is also essential to develop and evaluate new numerical visualisation tools. This is rather challenging since the impregnation is characterized by a full three-dimensional flow in a porous medium having an anisotropic, spatial- and time-dependent permeability. The new approach taken here is to implement such models in an all-purpose and commercial computational fluid dynamics software through custom written subroutines. The strategy has been to first verify and validate the modifications by 2D simulations and then demonstrate the full 3D capacity through one demonstrator.

  • 49. Andersson, Magnus
    Visualisation of the vacuum infusion process2003Inngår i: ICCM-14: 14th International Conference on Composite Materials : July 14-18, 2003, San Diego, California, USA, Dearborn, Mich: Society of Manufacturing Engineers, North American Manufacturing Research Institution, 2003Konferansepaper (Fagfellevurdert)
  • 50. Andersson, Magnus
    et al.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Långström, R.
    Luleå tekniska universitet.
    Development of guidelines for the vacuum infusion process2000Inngår i: Proceedings of the 8th International Conference on Fibre Reinforced Composites, FRC 2000: Centre for Composite Materials Engineering, University of Newcastle, UK, 13 - 15 September 2000 / [ed] A. G. Gibson, Cambridge: Woodhead Publishing Materials , 2000, s. 113-120Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The current trend towards increased use of vacuum infusion moulding for large surface area parts has increased the interest for an advanced modelling of the process. This paper presents a detailed experimental investigation of laminate thickness and out-of-plane flow front shape during impregnation of high permeability reinforcement on top of a non-crimp fabric reinforcement lay-up. The goal with the experiments is to increase the understanding of the process and to provide accurate data that can later be used for validation of numerical models. The laminate thickness was measured during impregnation with a stereoscopic digital speckle photography system and the flow front shape was determined by tracking of colour marks in the stacking. The laminate lay-ups studied are different combinations of non-crimp fabrics and flow layers while the resin used was a polyester developed specifically for vacuum infusion moulding. Results are presented both for the instantaneous thickness and the flow front shape for several different material combinations. It was found that the skewness of the flow front became more pronounced with increasing number of flow layers when the number of non-crimp fabric layers was kept constant. As a first step towards a complete numerical model of the impregnation process a simplified model for the compressibility and a proven model for permeability was implemented in a commercial CFD package that can handle moving boundaries and moving flow fronts. Only a qualitative comparison with experiments was done but the conclusion was that the overall behaviour of the model was encouraging. A validation of the numerical model based on the measurements in this paper is under development.

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