caa a22 4500 606198482 CHVBK 20210128100934.0 cr unu---uuuuu 210128e20150801xx s 000 0 eng 10.1007/s00348-015-2030-7 doi (NATIONALLICENCE)springer-10.1007/s00348-015-2030-7 Unsteady flow separation in a turbine diffuser [Elektronische Daten] [Pierre Duquesne, Yvan Maciel, Claire Deschênes] A three-dimensional unsteady flow separation in the straight diffuser of a model bulb turbine is investigated with planar two-component PIV measurements near the wall. The turbine is operated in two selected conditions that give rise to separation zones of different size and shape. The blockage effect induced by separation leads to a sudden drop in turbine efficiency and power extraction. The separation front fluctuates significantly both in location and in shape with no periodicity. From conditionally averaged results, it is deduced that the mean separation front is tilted azimuthally and that the mean separation skin friction line is composed of a saddle point on the diffuser side with one of its branches running along the diffuser bottom. Vortices and separation front critical points are analysed with POD-reconstructed instantaneous velocity fields. Separation surface vortices are generally bigger and stronger than turbulent vortices within or outside the separation zone, which suggests that different roll-up mechanisms are involved. The separation surface is irregular and is populated near the wall by a succession of foci and saddle points. Springer-Verlag Berlin Heidelberg, 2015 Duquesne Pierre Hydraulic Machine Laboratory (LAMH), Department of Mechanical Engineering, Laval University, Pavillon Adrien-Pouliot, 1065 Avenue de la Médicine, G1V 0A6, Quebec, Canada aut Maciel Yvan Fluid Mechanics Laboratory and Hydraulic Machine Laboratory (LAMH), Department of Mechanical Engineering, Laval University, Pavillon Adrien-Pouliot, 1065 Avenue de la Médicine, G1V 0A6, Quebec, Canada aut Deschênes Claire Hydraulic Machine Laboratory (LAMH), Department of Mechanical Engineering, Laval University, Pavillon Adrien-Pouliot, 1065 Avenue de la Médicine, G1V 0A6, Quebec, Canada aut Experiments in Fluids Springer Berlin Heidelberg 56/8(2015-08-01), 1-15 0723-4864 56:8<1 2015 56 348 https://doi.org/10.1007/s00348-015-2030-7 text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s00348-015-2030-7 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Duquesne Pierre Hydraulic Machine Laboratory (LAMH), Department of Mechanical Engineering, Laval University, Pavillon Adrien-Pouliot, 1065 Avenue de la Médicine, G1V 0A6, Quebec, Canada aut NATIONALLICENCE 700 1- Maciel Yvan Fluid Mechanics Laboratory and Hydraulic Machine Laboratory (LAMH), Department of Mechanical Engineering, Laval University, Pavillon Adrien-Pouliot, 1065 Avenue de la Médicine, G1V 0A6, Quebec, Canada aut NATIONALLICENCE 700 1- Deschênes Claire Hydraulic Machine Laboratory (LAMH), Department of Mechanical Engineering, Laval University, Pavillon Adrien-Pouliot, 1065 Avenue de la Médicine, G1V 0A6, Quebec, Canada aut NATIONALLICENCE 773 0- Experiments in Fluids Springer Berlin Heidelberg 56/8(2015-08-01), 1-15 0723-4864 56:8<1 2015 56 348