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  • 51.
    Cervantes, Michel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gustavsson, Håkan
    Natural wave frequencies in continuous casting moulds1998Inngår i: Proceedings of the 3rd European Conference on Continuous Casting, 1998Konferansepaper (Fagfellevurdert)
  • 52.
    Cervantes, Michel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gustavsson, Håkan
    On the use of the Squire-Long equation to estimate radial velocities in swirling flows2007Inngår i: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 129, nr 2, s. 209-217Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A method to estimate the radial velocity in swirling flows from experimental values of the axial and tangential velocities is presented. The study is motivated by the experimental difficulties to obtain this component in a draft tube model as evidenced in the Turbine-99 IAHR/ERCOFTAC Workshop. The method uses a two-dimensional nonviscous description of the flow. Such a flow is described by the Squire-Long equation for the stream function, which depends on the boundary conditions. Experimental values of the axial velocities at the inlet and outlet of the domain are used to obtain the boundary conditions on the bounded domain. The method consists of obtaining the equation related to the domain with an iterative process. The radial velocity profile is then obtained. The method may be applied to flows with a swirl number up to about Sw=0.25. The critical value of the swirl number depends on the velocity profiles and the geometry of the domain. The applicability of the methodology is first performed on a swirling flow in a diffuser with a half angle of 3 deg at various swirl numbers, where three-dimensional (3D) laser Doppler velocimeter (LDV) velocity measurements are available. The method is then applied to the Turbine-99 test case, which consists in a model draft tube flow where the radial inlet velocity was undetermined. The swirl number is equal to Sw=0.21. The stability and the convergence of the approach is investigated in this case. The results of the pressure recovery are then compared to the experiments for validation.

  • 53. Cervantes, Michel
    et al.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Unsteadiness and viscous losses in hydraulic turbines2006Inngår i: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 44, nr 2, s. 249-258Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The variation of the mechanical energy for the mean, oscillating and turbulent flows are considered. Their mean point out the contribution of the unsteadiness to the viscous losses and the turbulent production. A two-dimensional turbulent pulsating flow is investigated for different unsteady regimes to illustrate the effects of unsteadiness on the overall losses.

  • 54.
    Cervantes, Michel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gustavsson, Håkan
    Page, M.
    Engström, F.
    Turbine-99 III: a summary2006Inngår i: 23rd IAHR Symposium on Hydraulic Machinery and Systems: Yokohama, Japan, October 17 - 21, 2006 ; [conference proceedings], 2006, artikkel-id 117Konferansepaper (Fagfellevurdert)
  • 55.
    Cervantes, Michel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jalk, Mats
    MPC Metal Process Control AB.
    Kelvesjö, Håkan
    MPC Metal Process Control AB.
    Ohlsson, Willy
    MPC Metal Process Control AB.
    Metal flow controlPatent (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    A method and a system are for the control of a gas-containing hidden flow of molten metal in a space defined by a tubular device. From measurements in at least one predetermined layer of the metal flow in the space, an indication is obtained of the appearance of the flow which is compared with stored values. The result of the comparison is used for controlling at least one flow-affecting parameter in such a manner that a desired type of flow is provided at least in the layer.

  • 56.
    Cervantes, Michel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jansson, Ida
    Jourak, Amir
    Glavatskih, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Porjus U9A full-scale hydropower research facility2008Inngår i: Hydro technology and the evironment for the new century: 24th IAHR Symposium on Hydraulic Machinery and Systems, October 27 - 31, 2008, Foz do Iguassu, Brazil, Foz do Iguassu, 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Hydropower still faces complex scientific and technical challenges in order to secure the availability and reliability of the power plants despite more than a century of development. The main challenge is due to new market constrains such as electrical market deregulation and introduction of renewable sources of energy. The major problem is related to the dynamic of the rotor involving several fields: hydraulics, power engineering and mechanics. On the other side, the large and growing hydropower world market represents an opportunity for technically advanced companies offering better efficiency. The difficulty to scale rigorously any technical advance makes full-scale experiment a necessity. World unique facilities are available at Porjus, Sweden, for this purpose. The Porjus Hydropower Centre is composed of a Francis (U8) and a Kaplan (U9) turbine of 10 MW, each exclusively dedicated to education, research and development. In order to further investigate specific issues related to availability and reliability, a project was initiated in 2006. The main objective is to make U9 a full-scale hydropower laboratory able firstly to furnish the necessary data for the development of rotor-dynamic models but also turbines and bearings. To this purposes more than 200 sensors have been installed to measure displacements, forces, pressure, film thickness, strains... The work presents an overview of the newly upgrade facility as well as some of the problems faced during the instrumentation of the machine.

  • 57.
    Cervantes, Michel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lövgren, Magnus
    Radial velocity at the inlet of the Turbine-99 draft tube2007Inngår i: 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. 137-144Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Measurements of the axial, radial and tangential velocities at the inlet and downstream the cone of the Turbine-99 draft tube test case with wedge Pitot tubes are presented. The measurements were principally performed to evaluate the radial velocity: an unknown parameter of the Turbine-99 test case. The results show an acceptable agreement withprevious measurements for the yaw angle and axial and tangential velocities. The radial velocity is found to have very small amplitude at the inlet of the draft tube. The measurements downstream the cone indicates a larger tangential velocity while the radial velocity has a larger amplitude that at the inlet.

  • 58.
    Cervantes, Michel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Parida, Vinit
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Innovation och Design.
    Higher education in hydropower2006Inngår i: International Water Power and Dam Construction, ISSN 0306-400X, E-ISSN 1538-6414, Vol. 58, nr 7, s. 25-27Artikkel i tidsskrift (Annet vitenskapelig)
  • 59.
    Cervantes, Michel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Trivedi, Chirag
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Dahlhaug, Ole Gunnar
    Department of Energy and Process Engineering, Water Power Laboratory, Norwegian University of Science and Technology, Trondheim, Norwegian University of Science and Technology (NTNU), Trondheim.
    Nielsen, Torbjørn Kristian
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Francis-99 Workshop 1: steady operation of Francis turbines2015Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 579, artikkel-id 11001Artikkel i tidsskrift (Annet vitenskapelig)
  • 60.
    Cervantes, Michel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Trivedi, Chirag
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Dahlhaug, Ole Gunnar
    Department of Energy and Process Engineering, Water Power Laboratory, Norwegian University of Science and Technology, Trondheim, Norwegian University of Science and Technology (NTNU), Trondheim.
    Nielsen, Torbjørn Kristian
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Francis-99 Workshop 2: transient operation of Francis turbines2017Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 782, artikkel-id 11001Artikkel i tidsskrift (Annet vitenskapelig)
  • 61.
    Cervantes, Michel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Videhult, Sebastian
    GE Energy AS, NO-7465 Trondheim.
    Adaptive draft tube for increased efficiency2006Inngår i: International Water Power and Dam Construction, ISSN 0306-400X, E-ISSN 1538-6414, Vol. 58, nr 3, s. 43-45Artikkel i tidsskrift (Annet vitenskapelig)
  • 62.
    Cervantes, Michel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Videhult, Sebastian
    GE Energy AS, NO-7465 Trondheim.
    Increasing efficiency2006Inngår i: International Water Power and Dam Construction, ISSN 0306-400X, E-ISSN 1538-6414, Vol. 58, nr 4, s. 25-27Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The deregulation of electric markets as well as the introduction of renewable sources of energy such as wind and wave power in several countries has lead to a demand for different operating patterns of hydro power plants. Hydro plants are more frequently operated away from best efficiency, at part-load or full-load, and with an increased number of start-ups and shutdowns. These new market conditions involve new constraints for the hydro machines, which can lead to an overall un-optimised utilisation. An example of this is Sweden, where hydro plants mainly operate Francis and Kaplan turbines built between 1950 and 1970. As a result, an extensive period of renovation has started in the country. New machines need to be designed to take into account the new market conditions.

  • 63.
    Cervantes, Michel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Videhult, Sebastian
    Unsteady pressure measurements at Porjus U92003Inngår i: Hydraulic machinery and systems: proceedings of the XXIst IAHR symposium ; September 9 - 12, 2002, Lausanne / [ed] François Avellan, Lausanne: EPFL Laboratoire de Machines Hydrauliques , 2003Konferansepaper (Fagfellevurdert)
  • 64.
    Cervantes, Michel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Wallström, Åsa
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Industriell Ekonomi.
    Forskarskola för kvinnor omgång 4 (2009-2011)2008Inngår i: Genus i norrsken, ISSN 1654-7640, Vol. 1, nr 3-4Artikkel i tidsskrift (Annet vitenskapelig)
  • 65.
    Chitrakar, Sailesh
    et al.
    Kathmandu University, Nepal.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Thapa, Biraj Singh
    Kathmandu University, Nepal.
    Fully coupled FSI analysis of Francis turbines exposed to sediment erosion2014Inngår i: International Journal of Fluid Machinery and Systems, ISSN 1882-9554, E-ISSN 1882-9554, Vol. 7, nr 3, s. 101-109, artikkel-id 9Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sediment erosion is one of the key challenges in hydraulic turbines from a design and maintenance perspective in Himalayas. The present study focuses on choosing the best design in terms of blade angle distribution of a Francis turbine runner which has least erosion effect without influencing the efficiency and the structural integrity. A fully coupled Fluid-Structure-Interaction (FSI) analysis was performed through a multi-field solver, which showed that the maximum stress induced in the optimized design for better sediment handling, is less than that induced in the reference design. Some numerical validation techniques have been shown for both CFD and FSI analysis

  • 66. Cupillard, Samuel
    et al.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Glavatskih, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    A CFD study of a finite textured journal bearing2008Inngår i: Hydro technology and the evironment for the new century: 24th IAHR Symposium on Hydraulic Machinery and Systems, October 27 - 31, 2008, Foz do Iguassu, Brazil, Foz do Iguassu, 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    An analysis of a lubricated journal bearing is performed with special attention to the influence of textured surfaces which may improve hydrodynamic performance. The bearing is subjected to an external applied load and the force balance is fulfilled with the force of the flow acting on the bearing. The position of the shaft is fixed whereas the bearing, centred at the starting time, moves under the forces until equilibrium is reached. A mesh deformation technique is used with CFD (Computational Fluid Dynamics) in order to perform the simulations. The flow is laminar, isothermal, three-dimensional (3D) and unsteady. Cavitation is taken into account. Results are analysed with smooth and textured surfaces on the bearing. Friction force and eccentricity ratio are compared for different configurations.It is found that shallow grooves under light loading (ε < 0.15) enhance the minimum film thickness while reducing the friction force. Under high loading (ε > 0.5), deep grooves are able to reduce the friction force despite a reduced minimum film thickness. For the second case, the predicted performance is superior to those of a smooth journal bearing with thinner lubricant.

  • 67. Cupillard, Samuel
    et al.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Glavatskih, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Pressure buildup mechanism in a textured inlet of a hydrodynamic contact2008Inngår i: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 130, nr 2Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A flow analysis is carried out for an inclined slider bearing with the aim of showing the governing mechanism at conditions where an optimum in load carrying capacity is achieved. The effects of surface texture on pressure buildup and load carrying capacity are explained for a textured slider bearing geometry. Numerical simulations are performed for laminar, steady, and isothermal flows. The energy transferred to the fluid from the moving wall is converted into pressure in the initial part of the converging contact and into losses in the second part. The convergence ratio can be increased, in order to get the greatest pressure gradient, until the limiting value where flow recirculation begins to occur. The texture appears to achieve its maximum efficiency when its depth is such that the velocity profile is stretched at its maximum extent without incurring incoming recirculating flow. The wall profile shape controlling the velocity profile can be optimized for many hydrodynamic contacts

  • 68. Cupillard, Samuel
    et al.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Glavatskih, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Pressure build-up mechanism in a textured inlet of a slider bearing2007Inngår i: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, s. 33-Konferansepaper (Annet vitenskapelig)
  • 69.
    Cupillard, Samuel
    et al.
    Hydro-Québec Research’s Institute.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Glavatskih, Sergei
    Kungliga tekniska högskolan, KTH.
    Thermohydrodynamic analysis of a journal bearing with a microgroove on the shaft2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this study, thermohydrodynamic performance of a journal bearing with a microgroove created on the shaft is analysed. A plain journal bearing is modelled using a computational fluid dynamics (CFD) software package. Navier-Stokes and energy equations are solved. The rotor-stator interaction is treated by using a computational grid deformation technique. Results are presented in terms of typical bearing parameters as well as flow patterns. Results are also compared to the bearing with a smooth shaft. The effect induced by a microgroove on pressure distribution is explained for different bearing configurations, eccentricities and microgroove depths. It is shown that the microgroove produces a local drop in pressure which, averaged over one revolution, decreases the load carrying capacity. The load carrying capacity is further decreased by using deeper microgrooves. With thermal effects considered, the microgroove carries more cold lubricant into the warmest regions of the bearing. This effect, more pronounced with deeper microgrooves, is due to a global flow recirculation inside the microgroove, which improve mixing

  • 70. Cupillard, Samuel
    et al.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Glavatskih, Sergei
    Thermohydrodynamic analysis of a journal bearing with a microgroove on the shaft2014Inngår i: Computational Thermal Sciences, ISSN 1940-2503, E-ISSN 1940-2554, Vol. 6, nr 1, s. 47-57Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, thermohydrodynamic performance of a journal bearing with a microgroove created on the shaft is analyzed. A plain journal bearing is modeled using a computational fluid dynamics (CFD) software package. Navier-Stokes and energy equations are solved. The rotor-stator interaction is treated by using a computational grid deformation technique. The goal is to examine the pressure/temperature distribution in the bearing film. Results are presented in terms of typical bearing parameters as well as flow patterns. Results are also compared to the bearing with a smooth shaft. The effect induced by a microgroove on pressure distribution is explained for different bearing configurations, eccentricities, and microgroove depths. It is shown that the microgroove produces a local drop in pressure which, averaged over one revolution, decreases the load carrying capacity. The load carrying capacity is further decreased by using deeper microgrooves. With thermal effects considered, the microgroove carries more cold lubricant into the warmest regions of the bearing. This effect, more pronounced with deeper microgrooves, is due to a global flow recirculation inside the microgroove, which improves mixing

  • 71. Cupillard, Samuel
    et al.
    Glavatskih, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    3D thermodynamic analysis of a textured slider2008Inngår i: Proceedings of NORDTRIB 2008, 13th Nordic Symposium on Tribology: Scandic Rosendahl Hotel, Tampere, Finland, June 10 - 13, 2008 / [ed] Jaakko Kleemola; Arto Lehtovaara, Tampere: Tampere University of Technology, 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Analysis of a 3D inlet textured slider bearing with a temperature dependent fluid is performed. Numerical simulations are carried out for a laminar and steady flow. Hot and cold lubricant mixing in the groove is modelled and examined for different operating conditions. Thermohydrodynamic performance of the bearing is analysed for different texture lengths. Results show that texture has a stronger and positive influence on load carrying capacity when thermal effects are considered. This beneficial effect is at a maximum for the longest dimples with a length shorter than the pad length. Texture is also beneficial for the load carrying capacity when the sliding speed and inlet flow rate are varied: with an appropriate supply mass flow, load carrying capacity can be increased by 6-7% at low sliding speeds.

  • 72. Cupillard, Samuel
    et al.
    Glavatskih, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    3D thermohydrodynamic analysis of a textured slider2009Inngår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 42, nr 10, s. 1487-1495Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Analysis of a 3D inlet textured slider bearing with a temperature dependent fluid is performed. Numerical simulations are carried out for a laminar and steady flow. Hot and cold lubricant mixing in the groove is modelled and examined for different operating conditions. Thermohydrodynamic performance of the bearing is analysed for different texture lengths. Results show that texture has a stronger and positive influence on load carrying capacity when thermal effects are considered. This beneficial effect is at a maximum for the longest dimples with a length shorter than the pad length. Texture is also beneficial for the load carrying capacity when the sliding speed and inlet flow rate are varied. The load carrying capacity of the slider can be increased by up to 16% in severe operating conditions (high sliding speed).

  • 73. Cupillard, Samuel
    et al.
    Glavatskih, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Computational fluid dynamics analysis of a journal bearing with surface texturing2008Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 222, nr 2, s. 97-107Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An analysis of a lubricated conformal contact is carried out to study the effect of surface texture on bearing friction and load carrying capacity using computational fluid dynamics. The work focuses on a journal bearing with several dimples. Two- and three-dimensional bearing geometries are considered. The full Navier-Stokes equations are solved under steady-state conditions with a multi-phase flow cavitation model.The coefficient of friction can be reduced if a texture of suitable geometry is introduced. This can be achieved either in the region of maximum hydrodynamic pressure for a bearing with high eccentricity ratio or just downstream of the maximum film for a bearing with low eccentricity ratio. An additional pressure build-up produced as a result of the surface texture has been shown at low eccentricity ratios.

  • 74. Cupillard, Samuel
    et al.
    Glavatskih, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Effect of surface texturing on journal bearing performance2006Inngår i: ASIATRIB 2006: proceedings of the third Asia International Conference on Tribology, October 16-19, Kanazawa, Japan, Minato-ku: Kikai Shinkou Kaikan , 2006Konferansepaper (Fagfellevurdert)
  • 75. Cupillard, Samuel
    et al.
    Glavatskih, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Inertia effects in textured hydrodynamic contacts2010Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 224, nr 8, s. 751-756Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A flow analysis is carried out for a parallel textured slider to investigate the role of fluid inertia. Numerical simulations are performed for a laminar, two-dimensional, steady and isothermal flow. Stokes solutions are compared with Navier-Stokes solutions at the same Reynolds number. A range of texture depths is analysed. It is shown that there is an optimum value of texture depth that provides maximum load-carrying capacity. It is also shown that there is a critical depth value. Inertia has a negative effect on the load-carrying capacity for depths higher than the critical value, whereas it has a positive effect for lower depths. For a given texture depth, these effects are amplified as the Reynolds number increases. The global effect of inertia is positive when a realistic configuration of a parallel textured slider with a fore-region is considered.

  • 76. Cupillard, Samuel
    et al.
    Glavatskih, Sergei
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Thermal analysis of lubricant flow in a textured inlet contact2008Inngår i: Proceedings of the 19th International Symposium on Transport Phenomena (ISTP-19): Reykjavik, Iceland, August 17-21, 2008 / [ed] Sigurdur Brynjolfsson; Olafur Petur Palsson; Jong H. Kim, University of Iceland, Faculty of Industrial Engineering, Mechanical Engineering and Computer Science , 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Performance of an inlet textured contact is analysed for a temperature dependent lubricant flow. Thermal effects are analysed for different shear rates. Shearing of lubricant and subsequent heating reduce load carrying capacity and frictional losses compared with isothermal conditions. Load carrying capacity of a parallel surface contact can be improved by using texturing at the inlet when thermal effects are considered. It is also shown that for the different convergence ratios considered, the texture enables the sustaining of a load until a certain critical shear rate is reached. This critical shear rate depends on a number of factors such as the convergence ratio and lubricant parameters including the viscosity-temperature coefficient and the dynamic viscosity at reference temperature.

  • 77.
    Dehkharqani, Arash Soltani
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Amiri, Kaveh
    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.
    Steady and transient pressure measurements on the runner blades of a Kaplan turbine model2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The development of renewable energy sources has increased the need for power regulation. Power system regulation is mainly performed by hydropower plants through load variations. Additional forces are exerted on the runner blades during these load variations. This paper deals with pressure measurement performed on the blades of a Kaplan turbine model under steady state and load variation conditions. Flow behavior and frequency content of the pressure are investigated and compared to find critical condition in terms of pressure fluctuation. The results show that at various operating points and conditions, different regions of the blade are important. During load rejection, a considerable amount of pressure fluctuations are exerted on the runner blades. These results will be used to define experiments to be performed on the corresponding prototype. On the prototype, the loads acting on the runner blades will be investigated at various operation points similar to the model. In addition, the relation between the frequency content on the blades and loads on the main shaft will be investigated. Comparing results from model and prototype eventually would be valuable to explore the flow characteristics in prototype since CFD simulation of prototype is challenging.

  • 78.
    Dunca, Georgiana
    et al.
    Polytechnic University of Bucharest, Romania.
    Bucur, Diana
    Polytechnic University of Bucharest, Romania.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sensitivity analysis on flow rate estimation using design of experiments: Application to the pressure-time method2017Inngår i: 2017 10th International Symposium on Advanced Topics in Electrical Engineering, ATEE 2017, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 533-538, artikkel-id 7905035Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The present work investigates the flow parameters influence over the accuracy of flow rate determination by means of Design of Experiments -a statistical procedure widely used for experiments. The method used for the estimation of the flow rate derives from the standard pressure-time method, modified and improved - the solution is obtained by solving the water hammer equations considering an unsteady friction factor. The influence of the following parameters over the final moment of the flow rate variation regime is determined: the time of valve closure, the Reynolds number of the flow and the type of the closure law. A 23 factorial design is chosen to test the manner the three parameters influence, separately and together, the time value that should be chosen for the end of the flow rate variation regime. The results will help understand the influence of these parameters and the way in which they should be modeled within the flow rate determination method.

  • 79.
    Dunca, Georgiana
    et al.
    POLITEHNICA University of Bucharest.
    Bucur, Diana
    POLITEHNICA University of Bucharest.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Proulx, Gilles
    Hydro-Québec Research’s Institute.
    Dostie, Matheiu Bouchard
    Hydro-Québec Research’s Institute.
    Investigation of the pressure-time method with an unsteady friction2013Inngår i: Hydro 2013: International Conference and Exhebition : Promoting the Versalite Role of Hydro, 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The pressure-time method is used to determine the flow rate in hydraulic turbines. Over the years, developments of the method to improve its accuracy have been proposed, such as a time dependent friction (Jonsson) or a different upper integration limit (Adamkowski). The present work investigates these developments on measurements performed on a full-scale machine for different flow rates. The discharge computed values using pressure measurements are compared to ultrasound transit time measurements performed simultaneously. The results point out the significance of the developments on the final results; variations of 0.5% are obtained when combining Jonsson friction formulation and Adamkowski upper integration limit.

  • 80.
    Dunca, Georgiana
    et al.
    POLITEHNICA University of Bucharest.
    Bucur, Diana Maria
    POLITEHNICA University of Bucharest.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Popa, Radu
    POLITEHNICA University of Bucharest.
    Discharge evaluation from pressure measurements by a genetic algorithm based method2015Inngår i: Flow Measurement and Instrumentation, ISSN 0955-5986, E-ISSN 1873-6998, Vol. 46, s. 49-55Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents an alternative to the Gibson method, for discharge estimation of a turbine inside a hydropower plant. The method proposes a genetic algorithm which includes an integration procedure for the water hammer equations using the method of characteristics. The decision variables are represented by the steady-state regime discharge before the valve closure and the pipe friction factor. The recordings of pressure/differential pressure in measuring sections are used.

  • 81.
    Dunca, Georgiana
    et al.
    POLITEHNICA University of Bucharest.
    Bucur, Diana Maria
    POLITEHNICA University of Bucharest.
    Iovanel, Raluca Gabriela
    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.
    On The Use of the Water Hammer Equations with Time Dependent Friction During a Valve Closure, for Discharge Estimation2016Inngår i: Journal of Applied Fluid Mechanics, ISSN 1735-3572, E-ISSN 1735-3645, Vol. 9, nr 5, s. 2427-2434Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper presents a new method for in site discharge estimation in pressured pipes. The method consists in using the water hammer equations solved with the method of characteristics with an unsteady friction factor model. The differential pressure head variation measured during a complete valve closure is used to derive the initial flow rate, similarly to the pressure-time (Gibson) method. The method is validated with a numerical experiment, and tested with experimental laboratory measurements. The results show that the proposed method can reduce the discharge estimation error by 0.6% compared to the standard pressure-time (Gibson) method for the flow rate investigation.

  • 82.
    Dunca, Gerogiana
    et al.
    POLITEHNICA University of Bucharest.
    Bucur, Diana Maria
    POLITEHNICA University of Bucharest.
    Jonsson, Pontus
    Pöyry.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Discharge measurements using the Pressure-Time Method: Different evaluation procedures2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper analyzes the pressure-time method and its developments. The pressure-time method used to determine the discharge in hydraulic turbines is described and applied in a generic test case in well controlled laboratory conditions. Developments of the method are presented: a time dependent friction factor (proposed by Jonsson) and a different upper integration limit (proposed by Adamkowski). Laboratory experiments are used to compute the discharge using the pressure-time method in the standard and modified versions and the results are compared. The precision of the methods is verified by comparing the computed discharge values to the values measured with a magnetic flowmeter.

  • 83.
    Dunca, Gerogiana
    et al.
    POLITEHNICA University of Bucharest.
    Bucur, Diana Maria
    POLITEHNICA University of Bucharest.
    Jonsson, Pontus
    Pöyry SwedPower AB.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Discharge measurements using the Pressure-Time Method: Different evaluation procedures2014Inngår i: Polytechnical University of Bucharest. Scientific Bulletin. Series D: Mechanical Engineering, ISSN 1454-2358, Vol. 76, nr 4, s. 195-202Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper analyzes the pressure-time method and its developments. The pressure-time method used to determine the discharge in hydraulic turbines is described and applied in a generic test case in well controlled laboratory conditions. Developments of the method are presented: a time dependent friction factor (proposed by Jonsson) and a different upper integration limit (proposed by Adamkowski). Laboratory experiments are used to compute the discharge using the pressure-time method in the standard and modified versions and the results are compared. The precision of the methods is verified by comparing the computed discharge values to the values measured with a magnetic flowmeter.

  • 84.
    Gantasala, Sudhakar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Luneno, Jean-Claude
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Aeroelastic simulations of wind turbine using 13 DOF rigid beam model2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The vibration behavior of wind turbine substructures is mainly dominated by their first few vibration modes because wind turbines operate at low rotational speeds. In this study, 13 degrees of freedom (DOF) model of a wind turbine is derived considering fundamental vibration modes of the tower and blades which are modelled as rigid beams with torsional springs attached at their root. Linear equations of motion (EOM) governing the structural behavior of wind turbines are derived by assuming small amplitude vibrations. This model is used to study the coupling between the structural and aerodynamic behavior of NREL 5 MWmodel wind turbine. Aeroelastic natural frequencies of the current model are compared with the results obtained from the finite element model of this wind turbine. Quasi-steady aerodynamic loads are calculated considering wind velocity changes due to height and tower shadow effects. In this study, vibration responses are simulated at various wind velocities. The derived 13 DOF simplified model of the wind turbine enables to simulate the influence ofchange in parameters and operating conditions on vibration behavior with less computational effort. Besides that, the results of the simplified models can be interpreted with much ease.

  • 85.
    Gantasala, Sudhakar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Tabatabaei, Narges
    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.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Numerical Investigation of the Aeroelastic Behavior of a Wind Turbine with Iced Blades2019Inngår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, nr 12, artikkel-id 2422Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Wind turbines installed in cold-climate regions are prone to the risks of ice accumulation which affects their aeroelastic behavior. The studies carried out on this topic so far considered icing in a few sections of the blade, mostly located in the outer part of the blade, and their influence on the loads and power production of the turbine are only analyzed. The knowledge about the influence of icing in different locations of the blade and asymmetrical icing of the blades on loads, power, and vibration behavior of the turbine is still not matured. To improve this knowledge, multiple simulation cases are needed to run with different ice accumulations on the blade considering structural and aerodynamic property changes due to ice. Such simulations can be easily run by automating the ice shape creation on aerofoil sections and two-dimensional (2-D) Computational Fluid Dynamics (CFD) analysis of those sections. The current work proposes such methodology and it is illustrated on the National Renewable Energy Laboratory (NREL) 5 MW baseline wind turbine model. The influence of symmetrical icing in different locations of the blade and asymmetrical icing of the blade assembly is analyzed on the turbine’s dynamic behavior using the aeroelastic computer-aided engineering tool FAST. The outer third of the blade produces about 50% of the turbine’s total power and severe icing in this part of the blade reduces power output and aeroelastic damping of the blade’s flapwise vibration modes. The increase in blade mass due to ice reduces its natural frequencies which can be extracted from the vibration responses of the turbine operating under turbulent wind conditions. Symmetrical icing of the blades reduces loads acting on the turbine components, whereas asymmetrical icing of the blades induces loads and vibrations in the tower, hub, and nacelle assembly at a frequency synchronous to rotational speed of the turbine.

  • 86. 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 model2010Inngår 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. 85-92Konferansepaper (Fagfellevurdert)
    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.

  • 87.
    Gonzalez, Sergio Galvan
    et al.
    Mechanical Engineering Department, Universidad Michoacana de San Nicolas de Hidalgo.
    Ibarra-Bracamontes, Laura
    Mechanical Engineering Department, Universidad Michoacana de San Nicolas de Hidalgo.
    Diaz, Gildardo Solorio
    Mechanical Engineering Department, Universidad Michoacana de San Nicolas de Hidalgo.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Assement study of the RNG turbulence model for steady state swirling flow analysis in a draft tube2012Inngår i: Avances en Simulacion Computacional y Modelado Numerico: memorias del XI congreso internacional de métodos numéricos en ingeniería y ciencias aplicadas CIMENICS'2012, Isla de Margarita, Venezuela, 26 al 28 de marzo de 2012 / [ed] E. Dávila; G. Uzcátegui; M. Cerrolaza, Facultad de Ingeniería , Universidad Central de Venezuela , 2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The flow in a hydraulic turbine draft tube is a challenging industrial application for CFD because is characterized by a turbulent flow with different flow phenomena, e.g. unsteadiness, flow separation, swirling flow and strong adverse pressure gradient. Thus, its simulation is complex and time-consuming high computational capacities are required Additionally, adequate turbulence modeling is needed to predict such flows accurately. The objective of the present work is to investigate the accuracy of the Renormalization Group Theory (RNG) k-c turbulence model on the draft tube flow close to the best efficiency of the turbine. The effect of the discerization schemes on these models has been studied As the flow is significantlyaffected by the walls, two different grid concentrations near to the wall (y + I and y + 50) were evaluated The numerical results are compared to detailed experimental results at different section and discussed.

  • 88.
    Goyal, Rahul
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Indian Institute of Technology Roorkee.
    Bergan, Carl
    Waterpower Laboratory, Norwegian University of Science and Technology.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gandhi, Bhupendra K.
    Indian Institute of Technology Roorkee.
    Dalhaug, Ole Gunnar
    Waterpower Laboratory, Norwegian University of Science and Technology.
    Experimental investigation on a high head model Francis turbine during load rejection2016Inngår i: IOP Conference Series: Earth and Environment, ISSN 1755-1307, E-ISSN 1755-1315, Vol. 49, nr 8, artikkel-id 082004Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Francis-99 is a set of workshop aiming to determine the state of the art of high head model Francis turbine simulations (flow and structure) under steady and transient operating conditions as well as to promote their development and knowledge dissemination openly. The first workshop (Trondheim, 2014) was concerned with steady state operation. The second workshop will focus on transient operations such as load variation and start-stop. In the present work, 2-D particle image velocimetry (PIV) with synchronized pressure measurements performed in the draft tube cone of the Francis-99 test case during load rejection is presented. Pressure sensors were mounted in the vaneless space and draft tube cone to estimate the instantaneous pressure fluctuations while operating the turbine from the best efficiency point (9.8°) to part load (6.7°) with the presence of a rotating vortex rope (RVR). The time-resolved velocity and pressure data are presented in this paper showing the transition in the turbine from one state to another

  • 89.
    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.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Water Power Laboratory, Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim.
    Gandhi, Bhupendra K.
    Department of Mechanical and Industrial Engineering, Indian Institute of Technology, Roorkee.
    Vortex Rope Formation in a High Head Model Francis Turbine2017Inngår i: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 139, nr 4, artikkel-id 041102Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Francis turbine working at off-design operating condition experiences high swirling flow at the runner outlet. In the present study, a high head model Francis turbine was experimentally investigated during load rejection, i.e., best efficiency point (BEP) to part load (PL), to detect the physical mechanism that lies in the formation of vortex rope. For that, a complete measurement system of dynamic pressure, head, flow, guide vanes (GVs) angular position, and runner shaft torque was setup with corresponding sensors at selected locations of the turbine. The measurements were synchronized with the twodimensional (2D) particle image velocimetry (PIV) measurements of the draft tube. The study comprised an efficiency measurement and maximum hydraulic efficiency of 92.4±0.15% was observed at BEP condition of turbine. The severe pressure fluctuations corresponding to rotor-stator interaction (RSI), standing waves, and rotating vortex rope (RVR) have been observed in the draft tube and vaneless space of the turbine. Moreover, RVR in the draft tube has been decomposed into two different modes; rotating and plunging modes. The time of occurrence of both modes was investigated in pressure and velocity data and results showed that the plunging mode appears 0.8 s before the rotating mode. In the vaneless space, the plunging mode was captured before it appears in the draft tube. The physical mechanism behind the vortex rope formation was analyzed from the instantaneous PIV velocity vector field. The development of stagnation region at the draft tube center and high axial velocity gradients along the draft tube centerline could possibly cause the formation of vortex rope

  • 90.
    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, India.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Water Power Laboratory, Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim, Norway.
    Gandhi, B.K
    Department of Mechanical and Industrial Engineering, Indian Institute of Technology, Roorkee, India.
    Synchronized PIV and pressure measurements on a model Francis turbine during start-up2019Inngår i: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the experiments performed on a high head model Francis turbine during start-up. Synchronized time dependent pressure and velocity measurements were performed to investigate the instabilities in the turbine. A total of four steady state operating points, namely synchronous load, part load, best efficiency point, and high load are considered to perform the turbine start-up. The runner angular speed was observed to increase almost exponentially during the guide vane positions from completely closed to no load condition. The frequency of wave propagation due to the interaction between runner blades and guide vanes was observed to follow the trend of increase of runner angular speed. A vortex rope frequency was captured in the draft tube during synchronous load to part load of the start-up. Two different mechanisms, namely, the development of stagnation point and the available recirculation regions were observed to cause the formation of vortex rope in the draft tube.

  • 91.
    Goyal, Rahul
    et al.
    Department of Mechanical and Industrial Engineering, Indian Institute of Technology.
    Cervantes, Michel J.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Water Power Laboratory, Department of Energy and Process Engineering, Norwegian University of Science and Technology.
    Gandhi, Bhupendra K.
    Department of Mechanical and Industrial Engineering, Indian Institute of Technology.
    Characteristics of Synchronous and Asynchronous modes of fluctuations in Francis turbine draft tube during load variation2017Inngår i: International Journal of Fluid Machinery and Systems, ISSN 1882-9554, E-ISSN 1882-9554, Vol. 10, nr 2, s. 164-175Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Francis turbines are often operated over a wide load range due to high flexibility in electricity demand and penetration of other renewable energies. This has raised significant concerns about the existing designing criteria. Hydraulic turbines are not designed to withstand large dynamic pressure loadings on the stationary and rotating parts during such conditions. Previous investigations on transient operating conditions of turbine were mainly focused on the pressure fluctuations due to the rotor-stator interaction. This study characterizes the synchronous and asynchronous pressure and velocity fluctuations due to rotor-stator interaction and rotating vortex rope during load variation, i.e. best efficiency point to part load and vice versa. The measurements were performed on the Francis-99 test case. The repeatability of the measurements was estimated by providing similar movement to guide vanes twenty times for both load rejection and load acceptance operations. Synchronized two dimensional particle image velocimetry and pressure measurements were performed to investigate the dominant frequencies of fluctuations, vortex rope formation, and modes (rotating and plunging) of the rotating vortex rope. The time of appearance and disappearance of rotating and plunging modes of vortex rope was investigated simultaneously in the pressure and velocity data. The asynchronous mode was observed to dominate over the synchronous mode in both velocity and pressure measurements.

  • 92.
    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.
    Gandhi, Bhupendra K.
    Department of Mechanical and Industrial Engineering, Indian Institute of Technology, Roorkee.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Water Power Laboratory, Department of Energy and Process Engineering, Norwegian University of Science and Technology.
    Experimental study of mitigation of a spiral vortex breakdown at high Reynolds number under an adverse pressure gradient2017Inngår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 9, artikkel-id 104104Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The flow in the off-design operation of a Francis turbine may lead to the formation of spiral vortex breakdowns in the draft tube, a diffuser installed after the runner. The spiral vortex breakdown, also named a vortex rope, may induce several low-frequency fluctuations leading to structural vibrations and a reduction in the overall efficiency of the turbine. In the present study, synchronized particle image velocimetry, pressure, and turbine flow parameter (Q, H, α, and T) measurements have been carried out in the draft tube cone of a high head model Francis turbine. The transient operating condition from the part load to the best efficiency point was selected to investigate the mitigation of the vortex rope in the draft tube cone. The experiments were performed 20 times to assess the significance of the results. A precession frequency of 1.61 Hz [i.e., 0.29 times the runner rotational frequency (Rheingans frequency)] is observed in the draft tube cone. The frequency is captured in both pressure and velocity data with its harmonics. The accelerating flow condition at the center of the cone with a guide vane opening is observed to diminish the spiral form of the vortex breakdown in the quasi-stagnant region. This further mitigates the stagnant part of the cone with a highly dominated axial flow condition of the turbine at the best efficiency point. The disappearance of the stagnant region is the most important state in the present case, which mitigates the spiral vortex breakdown of the cone at high Reynolds numbers. In contrast to a typical transition, a new type of transition from wake to jet is observed during the mitigation of the breakdown. The obtained 2D instantaneous velocity fields demonstrate the disappearance region of shear layers and stagnation in the cone. The results also demonstrate the existence of high axial velocity gradients in an elbow draft tube cone.

  • 93.
    Goyal, Rahul
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Indian Institute of Technology, Department of Mechanics & Industrial Engineering, Roorkee .
    Gandhi, Bhupendra K.
    Department of Mechanical and Industrial Engineering, Indian Institute of Technology, Roorkee .
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    PIV measurements in Francis turbine: A review and application to transient operations2018Inngår i: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 81, nr 2, s. 2976-2991Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Penetration of solar and wind energy into the grid network has raised the concern for grid stability which is generally balanced by operating the hydropower plants over a wide range. This results in several issues, such as rotor-stator interaction (RSI), vortex breakdown, rotating vortex rope (RVR), pressure shocks, vibration, and noise which may lead to failure. Particle Image Velocimetry (PIV) has been used to understand several physical mechanisms in the flow at various operating conditions. A non-negligible uncertainty may arise in the measurements due to calibration, abbreviation, and distortion of the light. Various parameters such as laser sheet thickness, particle type, particle size, particle density, camera resolution, image size and number of images may affect the quality of the measurements. In the present work, a review of PIV measurements performed in hydraulic turbines, mainly Francis, has been carried out. The objective is to develop an experimental set up to perform steady and transient measurements on a model Francis turbine. A maximum deviation of 1.8% in absolute velocity is estimated in the present study as compared to 2–3% reported in the previously performed measurements on Francis turbines. The repeatability of transient measurements is also investigated by extracting two velocity points on a PIV plane

  • 94.
    Goyal, Rahul
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Indian Institute of Technology Roorkee.
    Gandhi, Bhupendra K.
    Indian Institute of Technology Roorkee.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Transient Pressure Measurements in the Vaneless Space of a Francis Turbine during Load Acceptances from Minimum Load2018Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 1042, artikkel-id 012009Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Increased penetration of solar and the wind impels the designers of the hydroelectric power generation unit to provide more flexibility in operation for the stability of the grid. The power generating unit includes turbine which needs to sustain sudden change in its operating conditions. Thus, the hydraulic turbine experiences more transients per day which result in chronic problems such as fatigue to the runner, instrument malfunctioning, vibrations, wear and tear etc. This paper describes experiments performed on a high model (1.5:1) Francis turbine for load acceptances from the minimum load. The experiments presented in the paper are the part of Francis-99 workshop which aims to determine the performance of numerical models in simulations of model Francis turbine under steady and transient operating conditions. The aim of the paper is to present the transient pressure variation in the vaneless space of a Francis turbine where high-frequency pulsations are normally expected. For this, two pressure sensors, VL1 and VL2, are mounted at the vaneless space, one near the beginning of the spiral casing and the other before the end of the spiral casing. Both are used to capture the unsteady pressure field developed in the space between guide vanes and runner inlet. The time-resolved pressure signals are analyzed and presented during the transient to observe the pressure variation and dominant frequencies of pulsations.

  • 95.
    Goyal, Rahul
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Grenoble-INP/CNRS/UJF-Grenoble 1, Grenoble, France.
    Gandhi, BK
    Indian institute of Technology, Roorkee, India.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Experimental Investigation of a High Head Francis Turbine Model During Shutdown Operation2019Inngår i: IOP Conference Series: Earth and Environment, Institute of Physics (IOP), 2019, Vol. 240, artikkel-id 022028Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Increased penetration of intermittent energy resources disturbs the power grid network. The frequency band of the power grid is normally controlled by automatic opening and closing of the guide vanes of hydraulic turbines. This has increased the number of shutdown cycles as compared to the defined ones for the normal operation of turbines. Turbine shutdown induced a significantly higher level of pressure fluctuations and unsteadiness in the flow field, decreasing its expected life. This paper presents experiments performed on a high head model Francis turbine during shutdown. The pressure and 2D Particle Image Velocimetry (PIV) measurements were performed to investigate the pressure fluctuations and flow instabilities in the turbine. The pressure sensors were mounted in the draft tube cone and vaneless space to measure the instantaneous pressure fluctuations. In the present study, the initial high load operating condition was considered to perform the turbine shutdown. The data were logged at the sampling frequency of 40 Hz and 5 kHz for PIV and pressure measurements, respectively. Time-resolved velocity and pressure data are presented in this paper to show the pressure fluctuations and causes of generation of unsteady flow in the draft tube.  

  • 96.
    Goyal, Rahul
    et al.
    Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee.
    Trivedi, Chirag
    Norwegian University of Science and Technology, Trondheim, .
    Gandhi, Bhupendra K.
    Indian Institute of Technology Roorkee.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Numerical Simulation and Validation of a High Head Model Francis Turbine at Part Load Operating Condition2018Inngår i: Journal of The Institution of Engineers (India): Series C, ISSN 2250-0545, Vol. 99, nr 5, s. 557-570Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydraulic turbines are operated over an extended operating range to meet the real time electricity demand. Turbines operated at part load have flow parameters not matching the designed ones. This results in unstable flow conditions in the runner and draft tube developing low frequency and high amplitude pressure pulsations. The unsteady pressure pulsations affect the dynamic stability of the turbine and cause additional fatigue. The work presented in this paper discusses the flow field investigation of a high head model Francis turbine at part load: 50% of the rated load. Numerical simulation of the complete turbine has been performed. Unsteady pressure pulsations in the vaneless space, runner, and draft tube are investigated and validated with available experimental data. Detailed analysis of the rotor stator interaction and draft tube flow field are performed and discussed. The analysis shows the presence of a rotating vortex rope in the draft tube at the frequency of 0.3 times of the runner rotational frequency. The frequency of the vortex rope precession, which causes severe fluctuations and vibrations in the draft tube, is predicted within 3.9% of the experimental measured value. The vortex rope results pressure pulsations propagating in the system whose frequency is also perceive in the runner and upstream the runner.

  • 97.
    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 turbine2016Inngår i: Sadhana (Bangalore), ISSN 0256-2499, E-ISSN 0973-7677, Vol. 41, nr 11, s. 1311-1320Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 98.
    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 software2017Konferansepaper (Fagfellevurdert)
    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.

  • 99.
    Iovane, Raluca G.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Bucur, Diana
    Polytechnic University of Bucharest, Romania.
    Dunca, Georgiana
    Polytechnic University of Bucharest, Romania.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Numerical analysis of a Kaplan turbine model transient operation2018Inngår i: IOP Conference Series: Earth and Environment, ISSN 1755-1307, E-ISSN 1755-1315, 2018Konferansepaper (Fagfellevurdert)
  • 100.
    Iovanel, Raluca Gabriela
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. University Politehnica of Bucharest, Romania.
    Bucur, D M
    University Politehnica of Bucharest, Romania.
    Dunca, G
    University Politehnica of Bucharest, Romania.
    Cervantes, Michel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Numerical analysis of a Kaplan turbine model during transient operation2019Inngår i: IOP Conference Series: Earth and Environmental Science, Institute of Physics (IOP), 2019, Vol. 240, artikkel-id 022046Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Hydropower plants are currently being intensively employed for electrical grid regulation. As a consequence, the frequency of start/stops and load variations is considerably increasing, leading to the operation of hydraulic turbines under improper conditions. During the last years, studies have focused on Francis turbines. The present paper aims to investigate a Kaplan turbine model. The flow through the turbine is modelled during transient operation, from the best efficiency point to a part load operating point, using a moving mesh for the guide vane displacement. The simulations are validated against experimental velocity profiles. A time step sensitivity analysis is performed in order to determine the optimum discretization time. The possibility of using large time steps is explored. The numerically simulated unsteady pressure pulsations on the runner blades are analysed. The influence of the inlet boundary conditions on the accuracy of numerical simulations is studied. The results show that a linear flow rate variation defined during the guide vane closure leads to an overestimation of the turbine head compared to the experimental value due to an overestimation of losses. The second type of boundary conditions, a constant total pressure, results in an underestimation of the flow rate compared to the experimental value due again to an overestimation of the losses.

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