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  • 1.
    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 and Development, Älvkarleby.
    Experimental investigation of the hydraulic loads on the runner of a Kaplan turbine model and the corresponding prototype2015Ingår i: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 53, nr 4, s. 452-465Artikel i tidskrift (Refereegranskat)
    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.Keywords: Bearing load; blade pressure measurement; flow-induced vibration; Kaplan turbine; prototype measurement; spiral casingperformance

  • 2.
    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 blade2013Konferensbidrag (Refereegranskat)
  • 3.
    Amiri, Kaveh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Mulu, Berhanu
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Raisee, Mehrdad
    School of Mechanical Engineering, University of Tehran, Mechanical Engineering Department, University of Tehran.
    Effects of load variation on a Kaplan turbine runner2016Ingår i: International Journal of Fluid Machinery and Systems, ISSN 1882-9554, E-ISSN 1882-9554, Vol. 9, nr 2, s. 182-193Artikel i tidskrift (Refereegranskat)
    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.

  • 4.
    Amiri, Kaveh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Mulu, Berhanu
    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.
    Experimental study on flow asymmetry after the draft tube bend of a Kaplan turbine2016Ingår i: Advances and Applications in Fluid Mechanics, ISSN 0973-4686, Vol. 19, nr 2, s. 441-472Artikel i tidskrift (Refereegranskat)
    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.

  • 5.
    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 runner2014Ingår 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, artikel-id 32005Konferensbidrag (Refereegranskat)
    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.

  • 6. Gererkiden, Berhanu Mulu
    et al.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    LDA measurements in a Kaplan spiral casing model2010Ingår i: 13th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery 2010 (ISROMAC-13): Honolulu, Hawaii, USA, 4 - 7 April 2010, Red Hook, NY: Curran Associates, Inc., 2010, s. 85-92Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents an experimental investigation of a Kaplan spiral casing turbine model. A two-component laser Doppler anemometry (LDA) apparatus was used to measure the velocity profiles at different locations in the turbine. To improve the signal quality and measurement accuracy, a refractive index matching optical box was mounted on the circular pipe of the spiral casing inlet. The investigations were carried out with a constant runner- blade angle and at three different loads: the best operating point of the turbine and two off-design operating points (left and right side of the propeller curve) with the presence of a vortex breakdown. The mean velocity profiles and corresponding RMS at the spiral casing before the guide vanes and at inlet of the spiral casing are presented for the different loads investigated.

  • 7. Jonsson, Pontus
    et al.
    Mulu, Berhanu
    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.
    Experimental investigation of a Kaplan draft tube: Part II: Off-design conditions2012Ingår i: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 94, nr 2, s. 71-83Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Off-design conditions of hydropower turbines are becoming more frequent with the deregulation of electricity markets and the introduction of renewable energy resources. Originally, turbines were not built to operate under such conditions. It is evident that there is a need to develop turbines that can operate under off-design conditions while attaining high efficiency. This may be achieved with computational fluid dynamics (CFD). However, the complexity of Kaplan turbine flows is challenging to treat using CFD. Therefore, detailed experimental investigations are necessary to validate and develop CFD. This paper presents an investigation of a modern design Kaplan turbine model. The measurements were performed in the draft tube with laser Doppler anemometry and flush-mounted pressure sensors, with a focus on the part load and high load operation of the turbine. Mean and phase-averaged quantities are presented for the velocity and pressure along several sections. A contra-rotating flow region was observed under high load operation. Under part load operation, a rotating vortex rope (RVR) develops due to vortex breakdown. The presence of the RVR significantly reduces the draft tube performance.

  • 8.
    Mulu, Berhanu
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    An experimental and numerical investigation of a Kaplan turbine model2012Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Hydropower is a renewable, reliable and highly efficient source of energy. Hydropower has the ability to run as a base load and to adjust load rapidly. This makes hydropower suitable for coupling with other renewable energy sources to stabilize frequency fluctuations. This ability has been used increasingly over the last decade due to the deregulation of the electricity markets and the introduction of other renewable energy sources, such as wind power. These changes have involved a substantial increase in the load variations and frequent start-stops. Such operating conditions may lead to unnecessary stresses and losses in turbines. Throughout the world, hydropower is the largest renewable source of energy. Currently, there is a need for refurbishment of old hydropower plants because most of them have reached the end of their design period. Efficiency may be improved by upgrading these older turbines. During the design or refurbishment phase of turbines, model testing and computational fluid dynamics (CFD) are the main tools available to predict, test and verify the performance as well as to investigate the flow characteristics.The use of CFD in the design and refurbishment process is becoming increasingly popular due to its flexibility, detailed flow description and cost effectiveness compared to model testing, which has been used over the last century of turbines development. However, issues still must be resolved due to the combined flow physics involved in hydropower machines, such as flow turbulence, separation, vortices, unsteadiness, swirl flow, strong adverse pressure gradients, convoluted geometry and numerical artifacts. Therefore, experimental data in such complicated systems are required to validate the numerical simulations and develop more accurate models.This thesis presents an experimental and numerical investigation performed on a reaction type axial water turbine. The investigation was performed on a model known as the Porjus U9. It is a geometrically similar model of the prototype turbine produced on a 1:3.1 scale. The main objectives were to characterize the flow phenomena in this modern Kaplan turbine model, to build a data bank for the validation of the CFD tools and to study the scale-up between the model and prototype, because the corresponding prototype is available for similar experiments. The investigation was performed at three different operating points: part load, best efficiency point (BEP) and high load. The technique used to investigate the flow was laser Doppler anemometry. The investigation was performed with time- and phase-averaged velocity measurements in several sections of the turbine where different periodic and non-periodic flow phenomena were captured. Some engineering quantities were also calculated to describe the turbine characteristics, such as the pressure recovery factor and the swirl number. At off-design operations, vortex breakdown was present.The numerical analysis of the model is also presented, where several RANS turbulence models were tested. The aim was to evaluate the capability of the turbulence models to predict the flow physics in the water turbines at the BEP. Validation was made with the experimental results in order to extend the range of confidence in the CFD results.

  • 9.
    Mulu, Berhanu
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Experimental and numerical investigation of axial turbine models2009Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Hydropower is a versatile renewable source of power generation able to change rapidly operating conditions. Hydropower plants may today work over a larger operating range than designed for due to the introduction of renewable sources of energy and the deregulation of the electricity market. Such operating conditions may involve large stresses and losses due to complex unsteady and transient flow phenomena, which have to be taken into account under design or refurbishment phase. The use of computational fluid dynamics (CFD) in the design and refurbishment process is becoming increasingly popular due to its flexibility, detailed flow description and cost-effectiveness comparing to model testing used since a century in the development of turbines. However, issues have still to be resolved due to the combined flow physics involved in hydropower machines such as partly separated flow at curved surfaces, vortices, unsteadiness, swirl flow, strong adverse pressure gradients, convoluted geometry as well as numerical artefacts. Therefore, experimental data in such complicated systems are required to validate numerical simulations and develop more accurate models.The first part of this thesis is a numerical investigation of the three-dimensional flow of the axial Hölleforsen model spiral casing and distributor, where the influence of the penstock on the flow is analysed using different turbulence models and inlet boundary conditions. Comparisons with experimental results indicate the importance of the penstock to perform accurate simulation in the present case. Therefore, detailed inlet boundary conditions are necessary to simulate accurately the spiral casing flows if the penstock is not included in the simulation.The second part of the thesis focuses on an experimental investigation of an axial hydropower turbine model known as Porjus U9. The measurements are part of a project aiming to investigate experimentally the flow in different regions of the machine to build a data bank in order to validate numerical simulations and study scale-up efficiency between model and prototype, since the corresponding prototype is available for similar experiments. The investigation was performed at 3 different working points: part load, best efficiency point and high load. The inlet flow of the spiral casing as well as some sections in the spiral casing and draft tube are investigated with a two components laser Doppler anemometer (LDA). To improve the signal quality and measurement accuracy refractive index matching optical box was mounted on the circular pipe of the spiral casing inlet. LDA result of the mean velocities and corresponding RMS are presented to investigate the flow before the runner and at the inlet of the spiral casing, since the flow is influenced by the existence of a bend before the inlet. The results of the draft tube measurements are also presented. Good quality data are obtained for initial boundary conditions at the inlet of the casing and drafttube cone to perform numerical simulations.

  • 10. Mulu, Berhanu
    et al.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Effects of inlet boundary conditions on spiral casing simulation2007Ingår i: Proceedings of the 2nd IAHR International Meeting of the Proceedings of the 2nd IAHR International Meeting of the Workgroup on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems, Timisoara,Romania, October 24-26, 2007 / [ed] R. Susan-Resiga; S. Bernad; S. Muntean, Timişoara, 2007, s. 217-226Konferensbidrag (Refereegranskat)
    Abstract [en]

    The results of numerical simulations of threedimensional turbulent viscous flow through the spiral casing and distributor of the Hölleforsen hydraulic turbine (Turbine-99 test case) are presented. Two CAD geometries, with and without the penstock, are analyzed in details to determine the effects of the upstream geometry, i.e. the inlet boundary conditions to the spiral casing. Conservation of mass and momentum equations of the flow are analysed using finite volume methods with the commercial software ANSYS CFX10.0. Standard k-ε with scalable wall function and SST k-ω based turbulence models are applied to study the flow characteristics. Comparisons are made between the numerical simulations with and without the penstock and available experimental results. The numerical results are found to more closely match with the experimental results when the penstock is included in the simulation. Therefore, detailed inlet boundary conditions are necessary to simulate accurately the spiral casing flows if the penstock is not included in the simulation. The numerical simulations also seem to show little sensitivity to the turbulence model.

  • 11. Mulu, Berhanu
    et al.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Effects of inlet boundary conditions on spiral casing simulation2007Ingår i: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, s. 53-Konferensbidrag (Övrigt vetenskapligt)
  • 12. Mulu, Berhanu
    et al.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Experimental investigation of a Kaplan model with LDA2009Ingår i: Water engineering for sustainable environment: 33rd IAHR congress ; 9 - 14 August 2009, Vancouver, British Columbia, Canada ; co-located with the 19th Canadian Hydrotechnical Conference, Madrid: IAHR , 2009, s. 155-162Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper describes the experimental investigation of a Kaplan turbine model of the Porjus U9 unit. The study aims to investigate the complex unsteady turbulent three-dimensional flow in different regions of the machine to build a data bank in order to validate numerical simulations and study scale-up efficiency between model and prototype. A two components LDA apparatus was used to measure the velocity profiles at different locations in the turbine in coincidence mode. An encoder pulse was used to resolve the measurements angularly. The investigation was carried out at three different loads: best operating point and two off-design operating points (left and right side of the propeller curve). Vortex breakdown was present at both off-design points at the inlet of the draft tube, in the cone. The axial and tangential mean velocity profiles and corresponding RMS at the draft tube cone are presented for the different loads investigated.

  • 13.
    Mulu, Berhanu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Cervantes, Michel
    Experimental investigation of a Kaplan turbine model with LDA2009Ingår i: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, s. 70-Konferensbidrag (Övrigt vetenskapligt)
  • 14.
    Mulu, Berhanu
    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.
    Phase resolved velocity measurements in a Kaplan draft tube model2011Konferensbidrag (Refereegranskat)
  • 15.
    Mulu, Berhanu
    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.
    Phase-resolved velocity measurements in a Kaplan draft tube model2011Ingår i: 4-th International Meeting on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems,: October, 26-28, 2011, Belgrade, Serbia / [ed] M. Nedeljkovic.; M. Benisek; A. Gajic, Belgrade: IAHR , 2011Konferensbidrag (Refereegranskat)
  • 16.
    Mulu, Berhanu
    et al.
    Vattenfall Research & Development.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Devals, Christophe
    Andritz Hydro Ltd, Computer and Software Engineering Department, Ecole Polytechnique de Montréal.
    Vu, T.C.
    Andritz Hydro Ltd.
    Gibault, F.
    Computer and Software Engineering Department, Ecole Polytechnique de Montréal.
    Simulation-based investigation of unsteady flow in near-hub region of a Kaplan Turbine with experimental comparison2015Ingår i: Engineering Applications of Computational Fluid Mechanics, ISSN 1994-2060, E-ISSN 1997-003X, Vol. 9, nr 1, s. 139-156Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    his paper presents a detailed comparison of steady and unsteady turbulent flow simulation results in the U9 Kaplan turbine draft tube with experimental velocity and pressure measurements. The computational flow domain includes the guide vanes, the runner and the draft tube. A number of turbulence models were studied, including the standard k-eps, RNG k-eps, SST and SST-SAS models. Prediction of the flow behavior in the conical section of the draft tube directly below the runner cone is very sensitive to the prediction of the separation point on the runner cone. The results demonstrate a significant increase in precision of the flow modeling in the runner cone region by using unsteady flow simulations compare to stage simulation. The prediction of the flow in the runner cone region, however, remains delicate, and no turbulence model could accurately predict the complex phenomena observed experimentally.

  • 17.
    Mulu, Berhanu
    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.
    Vu, Thi
    Andritz.
    Devals, Christophe
    Andritz.
    Guibault, Francois
    Polytechnique Montréal.
    Effects of inlet boundary conditions on Kaplan draft tube simulation accuracy2011Ingår i: HYDRO 2011 Proceedings: Prague, Czech Republic, 2011Konferensbidrag (Refereegranskat)
  • 18.
    Mulu, Berhanu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jonsson, Pontus
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Experimental investigation of a Kaplan draft tube: Part I: best efficiency point2012Ingår i: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 93, s. 695-706Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hydropower, originally designed as a base electrical power, is now used to balance grid fluctuations that are primarily produced by market deregulation and the introduction of other renewable energy resources. New turbine designs must account for such constraints while also achieving high efficiency. Computational fluid dynamics, now an integrated tool in the hydraulic industry, requires accurate and detailed experimental data for validation purposes.The present work presents the investigation of a modern Kaplan turbine model combined with laser Doppler anemometry and flush-mounted pressure sensors, with a focus on the draft tube at the best turbine efficiency. Mean and phase-resolved quantities are presented for the velocity and pressure at several locations. The results demonstrate the strong influence of the swirl leaving the runner for a well-functioning draft tube as well as the negative impact of the draft tube cone. The blade-hub clearance is also found to have an impact on the flow beneath the runner cone.

  • 19.
    Petit, Olivier
    et al.
    Chalmers University of Technology.
    Mulu, Berhanu
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Nilsson, Håkan
    Chalmers University of Technology.
    Cervantes, Michel
    Comparison of numerical and experimental results of the flow in the U9 Kaplan turbine model2010Ingår i: 25th IAHR Symposium on Hydraulic Machinery and Systems: 20-24 September 2010 'Politehnica' University of Timişoara, Timişoara, Romania, London: IOP Publishing Ltd , 2010, s. 12024-Konferensbidrag (Refereegranskat)
    Abstract [en]

    The present work compares simulations made using the OpenFOAM CFD code with experimental measurements of the flow in the U9 Kaplan turbine model. Comparisons of the velocity profiles in the spiral casing and in the draft tube are presented. The U9 Kaplan turbine prototype located in Porjus and its model, located in Älvkarleby, Sweden, have curved inlet pipes that lead the flow to the spiral casing. Nowadays, this curved pipe and its effect on the flow in the turbine is not taken into account when numerical simulations are performed at design stage. To study the impact of the inlet pipe curvature on the flow in the turbine, and to get a better overview of the flow of the whole system, measurements were made on the 1:3.1 model of the U9 turbine. Previously published measurements were taken at the inlet of the spiral casing and just before the guide vanes, using the laser Doppler anemometry (LDA) technique. In the draft tube, a number of velocity profiles were measured using the LDA techniques. The present work extends the experimental investigation with a horizontal section at the inlet of the draft tube. The experimental results are used to specify the inlet boundary condition for the numerical simulations in the draft tube, and to validate the computational results in both the spiral casing and the draft tube. The numerical simulations were realized using the standard k-e model and a block-structured hexahedral wall function mesh.

  • 20.
    Sundström, Joel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Mulu, Berhanu
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Wall friction and velocity measurements in multiple frequencies pulsating flow2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    Turbulent pulsating flow in a 100 mm diameter pipe has been studied experimentally at a Reynolds number of 14,500. The work covers four different flow conditions; steady, pulsating flow at oscillation frequencies 0.08 and 0.4 Hz, and pulsating flow with simultaneous imposition of both frequencies. The amplitudes of the pulsations were 10 and 7.5% of the bulk flow at 0.08 and 0.4 Hz, respectively. Laser Doppler anemometry, hot-film and pressure measurements show that the mean values of velocity, wall shear stress and pressure gradient are unaffected by the imposed pulsations. In agreement with previous studies of pulsating flow, the phase averaged pressure gradient leads both the velocity and wall shear stress when a single pulsation is imposed on the mean flow. These phase leads remain virtually unchanged when the two frequencies are imposed simultaneously. The amplitude responses of the velocity, wall shear stress and pressure gradient in the combined pulsating flow is shown to be superpositions of the amplitudes from the cases of separate pulsations. There are no signs of non-linear interactions between the harmonics.

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