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  • 301.
    Goyal, Rahul
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee.
    Trivedi, Chirag
    Norvegian University of Science and Technology.
    Gandhi, Bhupendra K.
    Indian institute of Technology, Roorkee, India.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Dahlhaug, Ole-Gunnar
    Norvegian University of Science and Technology.
    Transient pressure measurements at part load operating condition of a high head model Francis turbine2016Ingår i: Sadhana (Bangalore), ISSN 0256-2499, E-ISSN 0973-7677, Vol. 41, nr 11, s. 1311-1320Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hydraulic turbines are operating at part load conditions depending on availability of hydraulic energy or to meet the grid requirements. The turbine experiences more fatigue during the part load operating conditions due to flow phenomena such as vortex breakdown in the draft tube and flow instability in the runner. The present paper focuses on the investigation of a high head model Francis turbine operating at 50% load. Pressure measurements have been carried out experimentally on a model Francis turbine. Total six pressure sensors were mounted inside the turbine and other two pressure sensors were mounted at the turbine inlet pipe. It is observed that the turbine experiences significant pressure fluctuations at the vaneless space and the runner. Moreover, a standing wave is observed between the pressure tank outlet and the turbine inlet. Analysis of the data acquired by the pressure sensors mounted in the draft tube showed the presence of vortex breakdown co-rotating with the runner. The detailed analysis showed the rotating and plunging components of the vortex breakdown. The influence of the rotating component was observed in the entire hydraulic circuit including distributor and turbine inlet but not the plunging one

  • 302.
    Grane, Camilla
    et al.
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Arbetsvetenskap.
    Normark, Carl Jörgen
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Innovation och Design.
    Lundkvist, Andre
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Alm, Håkan
    Ågren, Anders
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Broström, Robert
    Volvo Car Corporation, Sverige.
    Davidsson, Staffan
    Volvo Car Corporation.
    Project: EFESOS - Environmental Friendly efficient Enjoyable and Safety Optimized Systems2012Övrigt (Övrig (populärvetenskap, debatt, mm))
    Abstract [sv]

    EFESOS is a Swedish Vehicle HMI (Human Machine Interaction) FFI research project. The overall ambition is to make driving of future cars more environmental friendly, enjoyable and safer by means of optimized systems. The project is managed by Volvo Car Corporation (VCC) and it is a collaboration between VCC and seven other research partners including Luleå University of Technology.

  • 303.
    Granström, Reine
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Modelling the aerodynamics of iron ore pelletizing kilns2012Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In an iron ore pelletizing plant, crude ore is upgraded to pellets to be used as feedstock in steel-making plants. As part of a grate-kiln pelletizing plant, the rotary kiln is an indurating furnace in which the pellets are sintered. The rotary kiln involves complex flow of large amounts of gas and the process is strongly coupled to the fluid dynamics, which is not well understood. The present work focuses on increasing the understanding of the aerodynamics of the rotary kiln.Though the kiln geometry is relatively simple a rather complex flow arises, which is known to occur for turbulent flows in similar geometries. In order to isolate the underlying flow mechanisms, simplified models of the kiln are studied both numerically using Computational Fluid Dynamics (CFD) and experimentally using Particle Image Velocimetry (PIV). The understanding of the flow phenomena that arises for the simplified models is essential for maintaining a solid comprehension of the fluid dynamics when increasing the complexity of the models. Computations are validated against available experimental data to evaluate the capability of the numerical procedure in capturing the underlying physics of the flow. In this way, the reliability of the predictions is improved when increasing the complexity of the model.In Paper A the unsteady non-reacting flow is computed and a preliminary coal combustion model is proposed, which is in need of further development to yield reliable predictions of the reacting flow. Paper B is an experimental investigation of a down-scaled model of the kiln and also an extension to previous experimental work by introducing an inclination of the upper inlet duct to the kiln and carrying out a more thorough analysis of the fluid dynamics. In Paper C, the periodic flow observed in Paper A is investigated further using a more sophisticated turbulence closure and carefully validating the predictions against available experimental data.For the simplified models under investigation, it is concluded that the flow is dominated by the periodic shedding and downstream convection of von-Karman-like vortices originating in the free shear layers enclosing the recirculation zone formed in the inlet end of the kiln. Both numerical and experimental investigations show a strong dependence of momentum flux ratio between the two inlet ducts on the flow field. The large-scale periodic fluctuations, which are resolved in an unsteady computation but completely neglected in a steady computation, are seen to contribute significantly to the turbulent transport in the recirculation zone. This indicates the need for unsteady computations to accurately predict the transport processes. The recirculation zone is important for flame stabilization as it feeds back hot gas to the near-burner region. Hence, a challenging requirement of the numerical model is to accurately capture the physics of the recirculating flow. The use of a second-moment turbulence closure is shown to significantly improve the predictions over the use of an eddyviscosity turbulence model and give promising results for further work on more complex models of the kiln.

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  • 304. Granström, Reine
    et al.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Marjavaara, Daniel
    LKAB.
    Töyrä, Simon
    LKAB.
    CFD modelling of the flow through a grate-kiln2009Ingår i: Proceedings from Seventh International Conference on Computational Fluid Dynamics in Minerals and Process Industries: CSIRO, Melbourne, Australia, 2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    As part of an investigation regarding secondary reduction of NOx emissions in a grate-kiln iron ore pelletizing plant, the aim of this specific research is to develop a CFD model that enhances the understanding of the aerodynamics and mixing of species inside the rotary kiln. At first, a parametric study of the pure airflow through the kiln is carried out and for certain conditions, a transient behaviour similar to that of vortex shedding was observed, with a dependence on momentum flux ratio between the secondary air jets. Further, the development of a preliminary coal combustion model is set out, which is in need of continued work in order to produce reliable predictions of various parameters relevant to the reduction process. However, the effect of the combustion on the flow field is limited, indicating that the pure airflow model can be used to broadly investigate the influence of the secondary air flow.

  • 305.
    Grecu, Ionuț Stelian
    et al.
    Department of Hydraulics, Hydraulic Machinery and Environmental Engineering, University POLITEHNICA of Bucharest.
    Bucur, Diana Maria
    Department of Hydraulics, Hydraulic Machinery and Environmental Engineering, University POLITEHNICA of Bucharest.
    Dunca, Georgiana
    Department of Hydraulics, Hydraulic Machinery and Environmental Engineering, University POLITEHNICA of Bucharest.
    Panaitescu, Valeriu Nicolae
    Department of Hydraulics, Hydraulic Machinery and Environmental Engineering, University POLITEHNICA of Bucharest.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Norwegian University of Science and Technology Trondheim.
    Implementation of the standard wall function in numerical computation software2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    The paper presents the validation of the implementation made by the user of the standard wall function for the standard k-ε turbulence model against the built-in standard wall function for the standard k-ε turbulence mode, in numerical computation software (ANSYS Fluent). A comparison was made between the results of two flow simulations: the first case consisted in using the built-in standard wall function and in the second case the implemented standard wall function was considered. The numerical simulations were made for the water flow inside a 3D diffuser. The results showed that both the wall functions used had a similar influence on the simulated flow.

  • 306.
    Grecu, Ionuț Stelian
    et al.
    Department of Hydraulics, Hydraulic Machinery and Environmental Engineering, University POLITEHNICA of Bucharest, Bucharest, Romania .
    Dunca, Georgiana
    Department of Hydraulics, Hydraulic Machinery and Environmental Engineering, University POLITEHNICA of Bucharest, Bucharest, Romania .
    Bucur, Diana Maria
    Department of Hydraulics, Hydraulic Machinery and Environmental Engineering, University POLITEHNICA of Bucharest, Bucharest, Romania .
    Cervantes, Michel J.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Wall-Layer Treatment Considering the Pressure Gradient for RANS Simulations of Turbulent Flows2019Ingår i: Proceedings of 2019 International Conference on ENERGY and ENVIRONMENT (CIEM), IEEE, 2019, s. 289-293Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The paper presents two wall-treatments employed with the standard k-ε turbulence model together with their consequences on the estimation of the flow characteristics (separation zone, velocity distribution, adverse/favourable pressure gradient, wall shear stress) and simulation resources (time and computational power). The two wall-treatments were developed by Manhart (2008) and Duprat (2010). The results are compared to those obtained with the standard k-ε turbulence model and the k-ω SST turbulence model, using the numerical computation software Code_Saturne CFD. The test case considered for the numerical simulations is a 3D diffuser geometry with water as fluid which undergoes flow separation. The results show that the two wall-treatments lead to an improvement of the accuracy in the prediction of the separation zone. The required time and computational power are improved, compared to the k-ω SST turbulence model.

  • 307.
    Green, Torbjörn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Particle image velocimetry in practice2009Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Experimental fluid mechanics has for a long time been used to visualize flow phenomenon. An early pioneer was Ludwig Prandtl who used aluminum particles in water flumes to describe the flow in a qualitative manner. In line with the rapid development of Computational Fluid Dynamics, CFD, the need for new validation tools has increased. By combining Prandtls attempt to trace particles and contemporary tools in laser and computer technologies a quantitative non intruisiv whole field technique, so called Particle Image Velocity (PIV) has been developed. The PIV technique has been improved and grown in popularity through recent decades with the increase in computer capacity. This thesis describes three rather different areas of application of PIV measurements. In the first case PIV is used as pure measurement technology tool to describe the flow field inside an attraction channel in connection to fish migration. In the second case, PIV is applied as a validation tool for CFD calculations with Large Eddy Simulation (LES) including an extensive analysis of the results. Finally, a description of how PIV technique can be adopted to study the flow of complex fluids in small geometries by means of microscopy is given.The attraction channel is a U-shaped channel designed to facilitate salmonoid like fihes to migrate upstream to their spawning grounds. The attraction channel has a restriction in the downstream outlet that provides an acceleration of the attraction water up to 38% of the sourunding water velocity according to the PIV measurements. With PIV measurements it is also shown that the depth of displacement over the restriction is significant for how far downstream the acceleration is perceptible. CFD technology is constantly evolving and new methods will become the future standard in the industry. In the current situation Reynolds Avereaged Numerical Simulations (RANS) is the most used method in CFD. But development is approaching LES technology. This is, for instance, motivated by energy production units which has many applications with high turbulence and temperature fluctuations. In the current situation it is required to extend the service life of existing power plants. Therefore it is desirable to be able to estimate these fluctuations impact on thermal loads on the materials inside the plant, for example pipe walls. An LES approach is superior to applying to RANS since the large eddies are resolved. However, LES is still not mature enough to be used without validation in critical applications. Therefore, PIV has been used to create a validation database for a generic T-junction.Double Restriction Sealings (DRS) have been used in bearings and other lubricated applications since the 1940's. A DRS is intended to prevent contamination from entering and is therefore used to increase the life span of lubricated parts, i.e. hinder polutants to reach the rolling elements in bearings for example. Although it is widly applied little is known about the actual function and mechanism of the DRS. To learn more about the flow and particle tracks within a DRS, a new method to visualize and quantify grease flow within a DRS has been developed based upon micro PIV. The main result from this study is that it is possible to make quantititative measurement of the flow within a DRS.

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  • 308.
    Green, Torbjörn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    PIV in Practice2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Experimental fluid mechanics has for a long time been used to visualize flow phenomenonqualitatively. Traditionally, visualization has been done with dye or tracer particle dueto their ability to follow the flow pattern well. One of the early pioneers in experimentalfluid mechanics was Ludwig Prandtl who used mica particles in water flumes to accuratelydescribe the flow around wing profiles. Due to Prandtl’s results in the early 20thcentury, some of the most important theories in aviation were founded. By combiningPrandtl’s attempt to trace particles, and contemporary laser and computer technologiesa quantitative non-intrusive whole field technique, so called Particle Image Velocimetry(PIV), has been developed. The PIV technique has through the advances in computerscience the recent decades, been improved significantly and has also grown in popularityamong the scientific- and technological community.This thesis describes implementation of PIV in several diverse research areas frommacro- to micro scale. First, it is described how PIV is used as a pure measurementtechnique to understand complex flow phenomena. The technique is demonstrated on asmall U-shaped channel designed to facilitate salmonoid like fishes upstream migrationto their spawning grounds. Second, PIV is used as a validation tool for ComputationalFluid Dynamics, CFD. In the current situation, CFD is undergoing a generation shiftfrom Reynolds Averaged Numerical Simulation, RANS, to Large Eddy Simulations, LES.This is for instance motivated by energy production units which has many applicationswith high turbulence and temperature fluctuations. Hence it is desirable to be able toestimate the impact on thermal loads on the materials inside the plant (e.g. the pipewalls). An LES approach is superior to applying to RANS since the large eddies areresolved. However, LES is still not mature enough to be used without validation incritical applications. Therefore, PIV has been used to create a validation database fora generic T-junction. Finally, a description of how PIV technique can be adopted tostudy the flow of complex fluids in small geometries by means of microscopy, is given andapplied on lubrication grease flow in labyrinth seals which have been used in bearingsand other lubricated applications since the 1940’s. The intention with labyrinth seals isto lubricate the bearing and prevent contamination from entering the rolling elements.Although it is widely applied, little is known about the actual function and mechanismof labyrinth seals. To learn more about the flow and particle migration within a sealgeometry, a new method to visualize and quantify grease flow within a labyrinth seal hasbeen developed based upon micro-PIV.

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  • 309.
    Green, Torbjörn
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Baart, Pieter
    Westerberg, Lars-Göran
    Lundström, Staffan
    Höglund, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Lugt, Piet
    Li, Jinxia
    A new method to visualize grease flow in a double restriction seal using microparticle image velocimetry2011Ingår i: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 54, s. 784-792Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new method to visualize and quantify grease flow in between two sealing lips or, in general, a double restriction seal is presented. Two setups were designed to mimic different types of seals; that is, a radial and an axial shaft seal. The flow of the grease inside and in between the sealing restrictions was measured using microparticle image velocimetry. The results show that grease flow due to a pressure difference mainly takes place close to the rotating shaft surface with an exponentially decaying velocity profile in the radial direction. Consequently, contaminants may be captured in the stationary grease at the outer radius, which explains the sealing function of the grease.

  • 310.
    Green, Torbjörn
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Baart, Pieter
    Westerberg, Lars-Göran
    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.
    Höglund, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Lugt, Piet
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Li, Jinxia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Visualisering och kvantifiering av fettströmning i lagertätningar med µPIV2011Konferensbidrag (Övrigt vetenskapligt)
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  • 311. Green, Torbjörn
    et al.
    Lindmark, Elianne
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gustavsson, Håkan
    Flow characterization of an attraction channel as entrance to fishways2011Ingår i: Rivers Research and Applications: an international journal devoted to river research and management, ISSN 1535-1459, E-ISSN 1535-1467, Vol. 27, nr 10, s. 1290-1297Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The flow field inside and downstream of an open channel placed near the surface of a free flow (such as the tail water of a turbine) is characterized in detail. The channel cross-section is U-shaped and in the downstream end is placed a ramp on the bottom which accelerates the flow passing through the channel. This flow is intended to catch the attention of fish and improve their entrance to fishways, which has also been successfully demonstrated in field tests.

  • 312.
    Green, Torbjörn
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Odemark, Y.
    Vattenfall Research & Development.
    Angele, K.
    Vattenfall Research & Development.
    Westin, J.
    Vattenfall Research & Development.
    Alavyoon, F.
    Forsmarks kraftgrupp AB.
    Lundström, Staffan
    Termisk utmattning av T-koppling: en jämförelse mellan LES och PIV2009Ingår i: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, s. 107-Konferensbidrag (Övrigt vetenskapligt)
  • 313.
    Green, Torbjörn
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Wassvik, Elianne
    Lundström, Staffan
    Gustavsson, Håkan
    Helfältsmätning av strömning genom lockvattenanordning2007Ingår i: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, s. 117-Konferensbidrag (Övrigt vetenskapligt)
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  • 314.
    Gustafsson, Göran
    Luleå tekniska universitet.
    Experiments on shock-wave focusing in an elliptical cavity1987Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 61, nr 11, s. 5193-5195Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experimental work on reflection and focusing of weak cylindrical shock waves in a liquid-filled elliptical cavity is presented. The shocks are generated at one focus of the cavity by electrical discharges, and converge at the other focus after reflection in the cavity wall. High-speed photographs of the resulting wave system, which appears to be considerably more complex than the corresponding one in air, are shown and discussed. The results are of interest in the design of a transient water-jet generator, which utilizes the energy in the converging shock wave to produce a fast liquid jet.

  • 315.
    Gustafsson, Göran
    Luleå tekniska universitet.
    Focusing of weak shock waves in a slightly elliptical cavity1987Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 116, nr 1, s. 137-148Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents theoretical work on the wave motion in an elliptical water jet generator. Such a device consists of a water filled elliptical cavity in which a shock wave is induced at one focus by a spark discharge. The shock converges to the other focus and via a convergent duct is allowed to reflect off a free surface of the liquid at the front of a nozzle, whereby a jet is emitted. The initial value problem of how a weak shock develops and how it is reflected from the walls of a cavity with small eccentricity is studied by using acoustic theory and a perturbation technique. In order to account for the distensibility of the wall material its admittance is introduced as a parameter. The validity of the results is extended to larger eccentricities by use of Padé approximants and by comparison with a geometrical acoustics solution to the same problem. The implications of the results on the design of the water jet generator are indicated.

  • 316.
    Gustafsson, Göran
    Luleå tekniska universitet.
    Propagation of weak shock waves in an elliptical cavity1985Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The propagation of weak shock waves in a planar elliptical cavity is studied theoretically and experimentally. The results are of interest in the design of an elliptical high-speed water jet generator operating in a transient fashion with electrically generated shocks in the acoustic regime. Perturbation theory and geometrical acoustics are used to find the resulting shock wave from the discharge. From this the reflected wave from the cavity walls is found through a condition incorporating the wall admittance. Padé approximants are employed to extend the validity of the solutions. The reflected wave is shown to be strongly dependent on the elliptical eccentricity, and the energy in its front is found to have a minimum for a particular, high value of this parameter. With the use of high-speed photography and schlieren technique experiments with a water filled cavity reveal a complex wave system in the liquid. A prominent feature is the appearance of a lateral wave. This is caused by wave motion in the wall, and conditions for when it is induced are derived. It will be absent if the product of eccentricity and propagation speed of the mode that causes it is less than the liquid sound speed. Experiments with a simple jet generator show that liquid jet speeds of the order of 100 m/s are easily attained. The long-time development of perturbations on the shock wave structure is derived. Different rates of approach to the asymptotic shock shape is found. The exact behavior appears to depend on certain combinations of parameters.

  • 317.
    Gustafsson, Göran
    Luleå tekniska universitet.
    The focused shock technique for producing transient water jets1983Ingår i: The second U.S. Water Jet Symposium, May 24, 25, 26, 1983, Rolla, Missouri / [ed] David A. Summers; Frank F. Haston, Rolla, MO: University of Missouri-Rolla , 1983Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents experimental work on a new type of transient water jet device. A spark discharge at one focus of a two-dimensional, elliptical, water filled cavity creates a shock wave which converges towards the other focus. There it enters an axisymmetric duct and is converted into a plane shock wave which moves out from the plane of the ellipse. When the plane wave reaches the free surface at the front of the nozzle a water jet is emitted. The Schliereren technique is used to study the process of wave convergence in the cavity. Resulting jet speeds form a simple non-optimized device are also measured. The fundamental idea appears to work and the results are promising, but difficulties remain.

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  • 318.
    Gustafsson, Göran
    Luleå tekniska universitet.
    The focused shock technique for producing transient water jets1984Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 319.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Direct resonance of nonaxisymmetric disturbances in pipe flow1989Ingår i: Studies in applied mathematics (Cambridge), ISSN 0022-2526, E-ISSN 1467-9590, Vol. 80, nr 2, s. 95-108Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    On considère un mécanisme qui peut conduire à la croissance algébrique, suivie d'une décroissance exponentielle de petites perturbations non axisymétriques dans un écoulement en conduite. Le mécanisme est interprété comme une résonance directe entre les perturbations de pression et de vitesse d'écoulement. Résolution numérique des problèmes de valeur propre pour les modes de pression et de vitesse. Influence du nombre de Reynolds

  • 320. Gustavsson, Håkan
    Dynamics of three-dimensional disturbances in water table flow1982Rapport (Övrigt vetenskapligt)
  • 321.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Energy growth of three-dimensional disturbances in plane Poiseuille flow1991Ingår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 224, s. 241-60Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The development of a small three-dimensional disturbance in plane Poiseuille flow is considered. Its kinetic energy is expressed in terms of the velocity and vorticity components normal to the wall. The normal vorticity develops according to the mechanism of vortex stretching and is described by an inhomogeneous equation, where the spanwise variation of the normal velocity acts as forcing. To study specifically the effect of the forcing, the initial normal vorticity is set to zero and the energy density in the wavenumber plane, induced by the normal velocity, is determined. In particular, the response from individual (and damped) Orr-Sommerfeld modes is calculated, on the basis of a formal solution to the initial-value problem. The relevant timescale for the development of the perturbation is identified as a viscous one. Even so, the induced energy density can greatly exceed that associated with the initial normal velocity, before decay sets in.

  • 322.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Excitation of direct resonances in plane Poiseuille flow1986Ingår i: Studies in applied mathematics (Cambridge), ISSN 0022-2526, E-ISSN 1467-9590, Vol. 75, nr 3, s. 227-248Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The direct resonance mechanism between vertical vorticity and vertical velocity is studied for plane Poiseuille flow. The resonance term, obtained from the initial-value problem, has been determined numerically for various initial disturbances. The amplitude, in wave-number space, is found to decay with time for all resonances. Because of its appearance in the Laplace-transform plane as a double pole, we show that a resonance term will have an initial amplitude which grows with Reynolds number, thus indicating that resonances will dominate the initial development of a disturbance at large Reynolds number.

  • 323.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Non-linear wave interactions from transient growth in plane-parallel shear flows2009Ingår i: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 28, nr 3, s. 420-429Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Based on the normal velocity-normal vorticity (v - η) formulation for the development of 3D disturbances in plane-parallel shear flows, the non-linear terms in the governing equations are derived as convolution integrals of the Fourier-transformed variables. They are grouped in three categories: v - v, v - η and η - η terms, and are expressed in a simple geometric form using the modulus of the two wave-vectors (k′ and k″) appearing in the convolution integrals, and their intervening angle (χ). The non-linear terms in the v-equation involving η are all weighted by sin χ (or sin2 χ). This confirms the known result that non-linear regeneration of normal velocity, necessary for a sustained driving of 3D disturbances, is not possible for stream-wise elongated structures (α = 0), only. It is therefore suggested how transiently amplified η can interact with decaying 2D waves to activate (oblique) waves which may be less damped than the 2D wave. This is shown to be possible for Blasius flow. In the η-equation, non-linear effects are possible for elongated structures resulting in shorter spanwise scales appearing at a shorter time-scale than the (linear) transient growth. A numerical example shows the details of this process in plane Poiseuille flow. From an inspection of the y-dependency (wall-normal direction) of the non-linear terms it is suggested that higher y-derivatives may give rise to non-linear effects in the inviscid development of perturbations. Also, a result for the y-symmetry of the non-linear terms is derived, applicable to plane Poiseuille flow.

  • 324.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Parameter study of direct resonance in water table flow1984Rapport (Övrigt vetenskapligt)
  • 325.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Resonant growth of three-dimensional disturbances in plane Poiseuille flow1981Ingår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 112, s. 253-264Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A linear mechanism for growth of three-dimensional perturbations on plane Poiseuille flow is investigated. The mechanism, resonant forcing of vertical vorticity waves by Tollmien-Schlichting waves, leads to an algebraic growth for small times. Eventually, viscous damping becomes dominant and the disturbance decays. The resonance occurs only at discrete points in the wave-number space. Nine resonances have been investigated. For these, the phase velocities range from 0.67 to 0.81 of the center-line velocity. The lowest Reynolds number for which the resonance can occur is 25. The strongest resonance appears only above a Reynolds number of 341. Also, two cases of degeneracy in the Orr-Sommerfeld dispersion relationship have been found.$

  • 326.
    Gustavsson, Håkan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Shanthini, Rajaratnam
    Luleå tekniska universitet.
    Degeneracies and direct resonances in water-table flow1990Ingår i: Studies in applied mathematics (Cambridge), ISSN 0022-2526, E-ISSN 1467-9590, Vol. 83, nr 1, s. 61-89Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Degeneracies of the Orr-Sommerfeld eigenmodes and direct resonances between the Orr-Sommerfeld eigenmodes and vorticity eigenmodes are studied in water-table flow. The sensitivity of the characteristics of these algebraic mechanisms to flow parameters, such as the Reynolds number (R), the slope of the table $(\theta)$, and the material parameter $(\gamma)$, are investigated. It is found that the mechanisms become operative at subtransitional R, and their damping rates decrease with increasing R. When the mean flow profile is slightly distorted from the ultimate parabolic profile, the characteristics of the direct resonances show remarkable variations. Also, some of the algebraic mechanisms in water-table flow are shown to have the same characteristics and modal structures as some of those in plane Poiseuille flow.

  • 327.
    Gustavsson, Håkan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Wallin, Stefan
    Luleå tekniska universitet.
    Effect of three-dimensional surface elements on boundary layer flow1990Ingår i: Structure of turbulence and drag reduction: Proceedings of the IUTAM Symposium / [ed] Albert Gyr, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 1990, s. 399-406Konferensbidrag (Refereegranskat)
    Abstract [en]

    The perturbation velocity field induced by a three-dimensional surface distortion in a boundary layer flow is considered. For small amplitudes, the kinetic energy is shown to be composed of two factors: one associated with the surface structure and the other with the velocity profile. Level curves of the profile factor, in the (alpha, beta) wavenumber plane, are ridge-like and approach the beta-axis as the Reynolds number increases. Thus, in the inviscid limit, the kinetic energy is confined to structures infinitely extended in the streamwise direction. For a certain class of surface structures, also the level curves for the kinetic energy have been determined. It is shown how a spanwise modulation and an aspect ratio of the surface distortion change the position of the level curves and the amplitudes.

  • 328.
    Gustavsson, Håkan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Nordlund, Erling
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Forsling, Willis
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Öhlander, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Forssberg, Eric
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Norrländsk vattenkraft och gruvnäring: två svenska välståndsbyggare2009Ingår i: Thule: Kungl. Skytteanska samfundets årsbok 2009, Umeå: Kungl. Skytteanska samfundet , 2009, s. 331-345Kapitel i bok, del av antologi (Övrig (populärvetenskap, debatt, mm))
  • 329.
    Gustavsson, Håkan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Ögren, Jan-Erik
    Luleå tekniska universitet.
    Observations of turbulent spots on a water table1982Rapport (Övrigt vetenskapligt)
  • 330.
    Gustavsson, Jonas
    Luleå tekniska universitet.
    The development of streamwise streaky structures in the suction boundary layer2000Rapport (Övrigt vetenskapligt)
    Abstract [en]

    An analytical solution is sought for the perturbation velocity field in a boundary layer with prescribed suction through a porous surface. Addressing the problem as an initial value problem, using stream- and spanwise Fourier transforms and Laplace transformation in time, yields solutions for the vertical velocity and the normal vorticity. Comparisons with the suction-free case are made and conclusions are drawn regarding the stabilizing effects of the suction motion. It is found that the analytical solutions give support to the theory that the presence of a porous boundary with suction acts stabilizing.

  • 331.
    Göhler, Martin
    et al.
    Luleå tekniska universitet.
    Ågren, Anders
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Noise radiation from a diesel engine: noise control investigations on the timing cover1991Rapport (Övrigt vetenskapligt)
  • 332.
    Göktepe, Burak
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Hazim, Ammar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    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.
    Cold flow experiments in an entrained flow gasification reactor with a swirl-stabilized pulverized biofuel burner2016Ingår i: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 85, s. 267-277Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Short particle residence time in entrained flow gasifiers demands the use of pulverized fuel particles to promote mass and heat transfer, resulting high fuel conversion rate. The pulverized biomass particles have a wide range of aspect ratios which can exhibit different dispersion behavior than that of spherical particles in hot product gas flows. This results in spatial and temporal variations in temperature distribution, the composition and the concentration of syngas and soot yield. One way to control the particle dispersion is to impart a swirling motion to the carrier gas phase. This paper investigates the dispersion behavior of biomass fuel particles in swirling flows. A two-phase particle image velocimetry technique was applied to simultaneously measure particle and gas phase velocities in turbulent isothermal flows. Post-processed PIV images showed that a poly-dispersed behavior of biomass particles with a range of particle size of 112-160 μm imposed a significant impact on the air flow pattern, causing air flow decelerated in a region of high particle concentration. Moreover, the velocity field, obtained from individually tracked biomass particles showed that the swirling motion of the carrier air flow gives arise a rapid spreading of the particles

  • 333.
    Göktepe, Burak
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Umeki, Kentaro
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Hazim, Ammar
    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.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Soot reduction in an entrained flow gasifier of biomass by active dispersion of fuel particles2017Ingår i: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 201, s. 111-117Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Soot is an undesired by-product of entrained flow biomass gasification since it has a detrimental effect on operation of the gasifier, e.g. clogging of flow passages and system components and reduction of efficiency. This study investigated how active flow manipulation by adding synthetic jet (i.e. oscillating flow through orifice) in feeding line affects dispersion of fuel particles and soot formation. Pine sawdust was gasified at the conditions similar to pulverized burner flame, where a flat flame of methane-air sub-stoichiometric mixture supported ignition of fuel particles. A synthetic jet flow was supplied by an actuator assembly and was directed perpendicular to a vertical tube leading to the center of the flat flame burner through which pine sawdust with a size range of 63–112 μm were fed into a reactor. Quartz filter sampling and the laser extinction methods were employed to measure total soot yield and soot volume fraction, respectively. The synthetic jet actuator modulated the dispersion of the pine sawdust and broke up particle aggregates in both hot and cold gas flows through generation of large scale vortex structures in the flow. The soot yield significantly reduced from 1.52 wt.% to 0.3 wt.% when synthetic jet actuator was applied. The results indicated that the current method suppressed inception of young soot particles. The method has high potential because soot can be reduced without changing major operation parameters.

  • 334.
    Hadi Jafari, Pantea
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    On the Influence from Turbulence Modeling on Particle Suspension Flow in Cyclone Gasifiers2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    Air-blown cyclone gasification is an entrained flow gasification process in which biomass powder fuel is burnt in a gasifier that operates similarly to a cyclone separator. Cyclone separators are widely used in industry to separate a dispersed solid phase (e.g. particles) from a continuous flow of gas based on density differences. Due to its simple design, the cyclone is a reliable apparatus with low cost for manufacture and maintenance.The performance of an isothermal cyclone separator can be predicted satisfactorily with the model developed by Muschelknautz et al. However, the flow in a non-isothermal cyclone gasifier has additional complexities, e.g. the production of gas from the fuel particles, that are outside the scope of the Muschelknautz model. In order to incorporate these effects more advanced modeling based on Computational Fluid Dynamics is needed. One problem with the CFD approach in combination with turbulent heat transfer and chemical reactions is that the complexity of the global model makes it difficult to assess the accuracy of the sub-models. Recently published models are based on relatively simple eddy-viscosity turbulence models. The agreement between these models and experiments has been encouraging but one cannot rule out the possibility that the apparently good performance of the model is a lucky coincidence due to cancellation of errors in the different sub models.The present paper is focusing on the fluid dynamics modeling of the flow in a cyclone gasifier in order to develop a better foundation for continued modeling. Since simulation of dispersed phase behavior is based on a precise modeling of the continuous phase flow field, it is valuable to assess different numerical approaches to find the most promising one for simulating the turbulent gas phase flow. Due to the complexity of turbulent swirling flow in a cyclone gasifier, a careful selection of turbulence models is needed to fulfill accurate numerical calculations of flow parameters. Two families of turbulence models are supposed to be tested: the two-equation eddy viscosity models including k-epsilon and k-omega, and the Reynolds stress model. For the k-epsilon model, steady-state and transient simulations are implemented. The gas cyclone of Obermair et al. with relevant operating conditions was chosen as a benchmark. The simulation results are compared to the Laser Doppler Anemometry (LDA) velocity measurements of the gas cyclone. The simulations are implemented in the commercial CFD (computational fluid dynamics) code ANSYS CFX 14.5; which uses an element-based finite volume approach. The method involves discretization of the spatial domain using a three-dimensional mesh to build up finite volumes over which relevant quantities like mass, momentum, and energy are conserved. In all, the capability of the mentioned approaches for representing the flow field in general and the precessing vortex core and its related fluctuations in particular will be discussed.

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  • 335.
    Hadi Jafari, Pantea
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Hellström, Gunnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Turbulence Modelling of a Single-Phase Flow Cyclone Gasifier2017Ingår i: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 9, nr 9, s. 779-799, artikel-id 79329Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The current work aims to make a foundation for an engineering design of a cyclone gasifier to be able not only to predict its flow field with a suitable accuracy but also to investigate a large number of design alternatives with limited computer resources. A good single-phase flow model that can form the basis in an Euler-Lagrange model for multi-phase flow is also necessary for modelling the reacting flow inside a cyclone gasifier. The present paper provides an objective comparison between several popular turbulence modelling options including standard k-ε and SST with curvature corrections, SSG-RSM and LES Smagorinsky models, for the single-phase flow inside cyclone separators/gasifiers that can serve as a guide for further work on the reacting multi-phase flow inside cyclone gasifiers and similar devices. A detailed comparison between the models and experimental data for the mean velocity and fluctuating parts of the velocity profiles are presented. Furthermore, the capabilities of the turbulence models to capture the physical phenomena present in a cyclone gasifier that affects the design process are investigated.

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    Turbulence Modelling of a Single-Phase Flow Cyclone Gasifier
  • 336.
    Hadi Jafari, Pantea
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Misiulia, Dzmitry
    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.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Modeling of Particle-Laden Cold Flow in a Cyclone Gasifier2018Ingår i: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 141, nr 2, artikel-id 021302Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Isothermal transient Eulerian–Lagrangian simulation of the turbulent gas–solid flow in a cyclone gasifier with two inlet tubes at 890 °C has been performed. The single-phase gas flow is modeled using SSG Reynolds stress turbulence model. Ten thousand representative solid particles of different sizes are injected from each inlet continuously at every second of simulation time. Particles are finally stopped as soon as they arrive at the outlet or reach the bottom plate of the gasifier. The effect of particle-to-gas coupling on the pressure and velocity of the flow and particles motion inside the gasifier is studied. The numerical approach can reasonably predict the impact of particle load on the gas flow as presented in the experimental results. Single particles are traveled throughout the transient gas flow field by using Lagrangian approach. High temperature of the gas flow inside the gasifier has significant effects on the swirl intensity reduction, damping the turbulence in the core region, pressure, and particle behaviors. However, the presence of solid particles does not have a notable influence on the swirl intensity and turbulence.

  • 337.
    Hadi Jafari, Pantea
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Risberg, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Numerical Simulation of Biomass Gasification in an Entrained Flow Cyclone Gasifier2020Ingår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 34, nr 2, s. 1870-1882Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A transient, two-way coupled Eulerian−Lagrangian computational fluid dynamics model has been developed for numerically investigating the gasification process of wood powder inside a cyclone-shaped reactor. The suggested model has considered heat and mass transfer, drying, devolatilization, and homogeneous and heterogeneous reactions. The model is validated using the experimental data from a commercial entrained-flow cyclone gasifier. The changes in gas composition as a function of equivalence ratio and the behavior of gasification process agreed well with the experimental measurement. Trajectories of individual particles were captured, and the behavior, mass fraction, and temperature distribution of several representative particles in different sizes were studied. Moreover, the model was successful in prediction of produced gas lower heating value, cold gas efficiency, and carbon conversion.

  • 338.
    Hadi Jafari, Pantea
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Wingren, Anders
    Meva Energy AB, Hisings Backa.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Effect of process parameters on the performance of an air-blown entrained flow cyclone gasifier2020Ingår i: International Journal of Sustainable Energy, ISSN 1478-6451, E-ISSN 1478-646X, Vol. 39, nr 1, s. 21-40Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Entrained flow gasification of biomass in a cyclone reactor combined by a gas engine has been applied in Nordic countries as one of the preferred methods for generating combined heat and power in small scales. The purpose of the current study was to optimise the gasification plant efficiency and understanding the influence of operating conditions. The experiments were carried out in a 2.4 MW(th) commercial gasification power plant. The gasifier was operated in optimum at a rather low lambda around 0.27 and a temperature of 950°C. The lower heating value of the clean product gas at this lambda was 5.95 MJ/Nm3. The experimental results also were compared with the predicted values from thermodynamic equilibrium calculations by Factsage 7.0. The performance of five different types of biofuels including torrefied spruce, peat, rice husk, bark and stemwood were assessed and compared with each other using thermodynamic equilibrium and available experimental data.

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  • 339.
    Hamedi, Naser
    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.
    Modelling of Flexible Fibres in Viscous Fluid Flow2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    The current study relates to the development of a multiphase model of flexible fibre suspensions. An understanding of the rheology and dynamics of the deformation of such suspension is desirable in order to be able to fully disclose the flow behaviour from very low to very high shear rates. We present an approach for numerically simulating the dynamics of flexible fibres employing a particle-level method. This is performed by investigating the fibre dynamics against several orbit classes - i.e. rigid, springy, flexible and complex rotation of the fibres [1-3] enabling the model to have all degrees of freedom (translation, rotation, bending and twisting). The three-dimensional Navier-Stokes equations which describes the fluid motion are employed while the fibrous phase of the fluid is modeled as chains of fiber segments interacting with the fluid through viscous- and drag forces. The simulations are performed using OpenFOAM and the numerical outcomes are validated against experimental data.The purpose of the modelling framework applied in this work is to enable the numerical model to be extended to a 4-way coupling model, capturing shear thinning, shear thickening and the yield stress properties of a fibrous fluid suspension.

  • 340.
    Hamedi, Naser
    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.
    On the deformation of fibrous suspensions2019Ingår i: Transactions of the Nordic Rheology Society, Nordic Rheology Society , 2019, Vol. 27Konferensbidrag (Refereegranskat)
    Abstract [en]

    An understanding of the rheology and dynamics of the deformation of fibrous suspension as a multiphase fluid is important in order to be able to fully disclose the flow behaviour from very low to very high shear rates. In this study, a flexible fibre model has been implemented in an open source Computational Fluid Dynamics code. The three-dimensional Navier-Stokes equations which describe the fluid motion are employed while the fibrous phase of the fluid is modeled as chains of fiber segments interacting with the fluid through viscous- and drag forces. The aim of this study is to investigate the fibre dynamics against several orbit classes - i.e. rigid, springy, flexible and complex rotation of the fibres1-3 enabling the model to have all degrees of freedom - translation, rotation, bending and twisting. The simulations are performed using the OpenFOAM open source software.

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  • 341.
    Hamedi, Naser
    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.
    On the Interaction of Side-By-Side Circular Cylinders in Viscoplastic Fluids2019Ingår i: Fluids, ISSN 2311-5521, Vol. 4, nr 2, artikel-id 93Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the static interaction of a train of three cylinders in a Bingham fluid is studiednumerically using Computational Fluid Dynamics. The variation of drag forces for the cylinders inseveral configurations is investigated. Positions of the particles in relation to the reference particleare recognized by the separation distance between the cylinders. A steady state field is considered,with Bingham numbers between 5 and 150. Several separation distances (d) were considered, such that2.0D d 6.0D where D is the cylinder diameter. The Reynolds number was chosen in the range of5 Re 40. In particular, the eect of the separation distance, Reynolds number and Bingham numberon the shape and size of the unyielded regions was investigated. The functional dependence of thisregion and the drag coecient is explored. The present results reveal the significant influence of thegap between the cylinders on the drag force and the shape of the unyielded regions surrounding thecylinders. It was found that there are several configurations in which the drag forces over the first andthe third cylinders are almost equal depending on variation of the Bi, Re and the separation distance.

  • 342.
    Hammami, A.
    et al.
    U. A. E. University, Al-Ain.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Analysis of the vacuum infusion molding process2000Ingår i: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 21, nr 1, s. 28-40Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The vacuum infusion molding process is becoming increasingly popular for the production of large composite parts. A comprehensive model of the process has not been proposed yet, making its optimization difficult. The flexible nature of the vacuum bag coupled to the varying pressure inside the mold cavity results in a variation of the cavity thickness during the impregnation. A complete simulation model must incorporate this phenomenon. In this paper, a complete analysis of the vacuum infusion molding process is presented. The analysis is not restricted to the theoretical aspects but also reviews the effect of the main processing parameters. The parameters investigated in this paper are thought to be those of most interest for the process, i.e. the compaction of the reinforcement, the permeability, the infusion strategy and the presence of flow enhancement layers. Following the characterization experiments, a 1-D model for the vacuum infusion molding process is presented. This model is derived assuming that an elastic equlibrium holds in the mold cavity during mold filling. Even though good agreement was found between simulation results and experiments, it is concluded that additional work is needed on the numerical model to integrate interesting findings from the experimental part.

  • 343.
    Hammar, Carsten
    et al.
    Skogshälsan, Boden.
    Eriksson, Ingvar
    Skogshälsan, Boden.
    Sundbäck, Ulrik
    Luleå tekniska universitet.
    Tingvall, Bror
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Helkroppsvibrationer i skogsmaskiner: skördare1980Rapport (Övrigt vetenskapligt)
  • 344.
    Hammargren, Kristoffer
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Aerodynamics Modeling of Sounding Rockets: A Computational Fluid Dynamics Study2018Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
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  • 345.
    Hansson, Mats
    Luleå tekniska universitet.
    Vibration and stress in frame and driver's cabin on a dump truck: comparision Skega Dump Body vs. a conventinal steel dump body1986Rapport (Övrigt vetenskapligt)
  • 346.
    Hatem, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Rheological Properties of Cement-Based Grouts Determined by Different Techniques2014Ingår i: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 6, nr 5, s. 217-229Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The rheological properties of cement-based grouts containing talc or palygorskite were investigated for optimizing fluidity and quick strengthening at injection. The fluidity controls the ability of grout to penetrate fractures and can be determined by pipe flow tests, Marsh funnel tests, mini-slump cone tests and rheometer tests. The grouts were 1) Talc for fluidity and strength by reacting with cement, 2) Palygorskite (attapulgite) for early gelation by being thixotropic, and 3) Powdered quartz for chemical integrity. The freshly prepared grouts behaved as Bingham fluids with viscosities from 0.151 to 0.464 Pas and yield stresses 5.2 Pa to 36.7 Pa. Statistical analysis of the flow test data converted Marsh flow time into viscosity. The pipe flow tests gave 26.5% higher values than the viscometer for grout with Portland cement and talc, and about 13.7% lower than the viscometer data for the grout with low-pH cement and talc. The big Marsh funnel gave valuesdiffering by 5.2% - 5.3% from those of the viscometer for grout with talc and Portland, and Merit 5000 cements. For grout with palygorskite the viscosity was at least twice that of the other grouts. Grout fluidity was positively affected by talc and negatively by palygorskite and early cement hydration

  • 347.
    Haupt, Dan
    et al.
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Medicinsk vetenskap.
    Nord, Kent
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Medicinsk vetenskap.
    Tingvall, Bror
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Ahlvik, Peter
    Ecotraffic ERD3 AB.
    Egebäck, Karl-Erik
    Autoemission KE E Concultant.
    Andersson, Sören
    STT EMTEC.
    Blomquist, Micael
    STT EMTEC.
    Investigating the potential to obtain low emissions from a diesel engine running on ethanol and equipped with EGR, catalyst and DPF2004Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Experiments were performed to investigate the potential to achieve low emissions from a diesel engine fueled by ethanol and equipped with a commercially available exhaust after-treatment device, DNO\dx\sT from STT Emtec. The DNO\dx\sT system includes exhaust gas recirculation (EGR) catalysts and a continuously regenerating diesel particulate filter (DPF). Two Euro III classified 9-liter turbocharged, after-cooled diesel engines from Scania were used for the task. One engine was fueled by ethanol and the other by Swedish diesel fuel, EC1. Engine operating conditions of a 22-mode test cycle, including the 13 modes of the European Stationary Cycle (ESC cycle), were used for the tests. The emissions of NO\dx and HC were small for the ethanol-fueled engine, 3.48 and 0.53 g/kWh, respectively, while the emission of CO was higher, 2.07 g/kWh. Estimations of emitted particle mass were calculated by using the software supplied in the Scanning Mobility Particle Sizer (SMPS). The estimations showed that the ethanol engine emitted only \mA1/10 of the particle mass emitted by the diesel-fueled engine. A powerful reduction of the regulated emissions was obtained when equipping the ethanol engine with EGR, catalyst and DPF. The emissions of HC, CO and NO\dx decreased down to 0.15, 0.04 and 2.54 g/kWh, respectively, while the estimated particle mass was reduced by 67%. Actually, by using the aftertreatment system, the engine became a Euro IV engine regarding the emissions of HC, CO and NO\dx. The system worked even better with the diesel-fueled engine. The NO\dx emission was reduced by approximately 33% and the estimated particle mass by more than 99%. Calculations showed that the EGR ratio was higher for the diesel engine than for the ethanol engine. Consequently, by applying a higher EGR ratio for the ethanol engine an additional reduction of the NO\dx emissions should be obtained. The results indicate that very low NO\dx and particle emissions could be obtained for an ethanol-fueled diesel engine by using the right aftertreatment equipment. Future studies should investigate the possibility to increase the EGR ratio further. The investigations also underline the need for development of a special particulate filter for ethanol engines.

  • 348. Haupt, Dan
    et al.
    Nordström, Fred
    Luleå tekniska universitet.
    Niva, Merja
    Luleå tekniska universitet.
    Bergenudd, Lennart
    Luleå tekniska universitet.
    Hellberg, Stig
    Luleå tekniska universitet.
    Undersökning av reglerade och några oreglerade emissioner från motorer drivna med blandbränsle, dieselolja och etanol1997Rapport (Övrigt vetenskapligt)
  • 349. Haupt, Dan
    et al.
    Westerholm, Roger
    Luleå tekniska universitet.
    Christensen, Anders
    Törnqvist, Margareta
    Luleå tekniska universitet.
    Ehrenberg, Lars
    Luleå tekniska universitet.
    Chemical and biological characterisation of exhaust emissions from ethanol and ethanol blended diesel fuels in comparison with neat diesel fuels1997Rapport (Övrigt vetenskapligt)
  • 350.
    Hazim, Ammar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Non-Spherical Particle Interaction in Duct and Jet Flow2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Wood waste is the most popular biomass recourse for many nations. Burned wood can, direct or indirect, release one of the greenhouse gases, carbon dioxide. The process can still be seen as a renewable source of energy since replanting of the trees and crops are consuming nearly the same amount of carbon dioxide through photosynthesis. Thermal gasification is one of the efficient methods to utilize energy from wood waste. Products from the component of concern can be used for direct energy production like in boilers and gas turbines or indirectly via dimethyl ether (DME), for instance. The physics of gasification is complex and several issues can influence the process. There is a lack of knowledge of several phenomena, some of which are related to solid-gas flow in the gasifier and in the premixed feeding pipelines. One such area is mechanisms related to turbulence modulation in the presence of spherical and non-spherical particles and how much the flow can disturb the motion of the particles. This is studied in the present thesis and the motion of the particles in different flow field is disclosed. At the moment there is no agreement in the scientific community on a single dimensionless number that can safely describe the influence of spherical particles in turbulent flow. For non-spherical particles additional levels of freedom are introduced and the dependence on drag and lift from the orientation of the particles as a function of Reynolds number adds to the complexity.Based on a literature review a fundamental experimental study is carried out in simple flow field geometry, a 2D duct flow. The aim is to reveal the influence of spherical glass particle on the turbulent flow field in the core and near wall flows. Additional studies with wood particles gave more information about how real biomass particles affect the turbulence as compared to spherical ones. Next the instantaneous distribution of biomass particles was studied experimentally. It is known that this distribution significantly influences the soot formation in a gasifier. Two different techniques of flow control were studied, swirling flow and synthetic jet flow. Particles shape and inertia and the strength of vortices and vortices interaction in coaxial jets and swirling jet flow were studied and yielded a high influence on the preferential concentration of particles as well as on the root mean square values for velocity in coaxial jets flow. The synthetic jet add momentum to the flow without disturbing the mass loading ratio and result in higher dispersion of the particles away from the centreline of the jet.

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