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Capturing vortical structures at low load in a Francis-99 turbine draft tube with RANS and hybrid RANS/LES models.

A. A. Gavrilov
Institute of Thermophysics of SB RAS, Krasnoyarsk branch, 50/44 Akademgorodok, ICM SB RAS, TORINS, Krasnoyarsk, 660036; Institute of Thermophysics of SB RAS, Ac. Lavrentieva ave. 1, Novosibirsk, Russian Federation, 630090; Novosibirsk State University, Pirogova st., 2, Novosibirsk, Russian Federation, 630090

A. V. Sentyabov
Institute of Thermophysics, SB RAS, Lavrentyeva 1, Novosibirsk; Novosibirsk State University, Pirogova st., 2, Novosibirsk, Russian Federation, 630090; Siberian Federal University, Svobodniy 79, Krasnoyarsk, Russia

A. A. Dekterev
Institute of Thermophysics of SB RAS, Krasnoyarsk branch, 50/44 Akademgorodok, ICM SB RAS, TORINS, Krasnoyarsk, 660036; Institute of Thermophysics, Siberian Branch of the Russian Academy of Sciences, 1 Akad. Lavrentiev Ave., Novosibirsk, 630090

K. Hanjalic
Department of Multi-scale Physics, Faculty of Applied Sciences, Delft University of Technology, The Netherlands and Novosibirsk State University, Russia

Résumé

Recognizing the inability of the conventional linear-eddy-viscosity RANS models to reproduce complex three-dimensional unsteady flows in hydraulic machinery, we report on a comparative assessment of performances of a second-moment (Re-stress) RANS closure and a hybrid RANS/LES method in reproducing flow and vortical structures in draft tube of a Francis hydroturbine. Multiple unsteady vortex systems detected at off-design conditions pose a special challenge and we considered a case of part load at a flow rate of only 35% of the best efficiency point. Both approaches reproduced reasonably well the measured mean velocity and the rms of its fluctuations, as well as pressure spectrum with peaks detecting precessing vortex core. While the Re-stress model showed to be more receptive to intrinsic unsteadiness than the k-ε RANS model, the hybrid RANS/LES method proved still superior in reproducing a wider range of scales of the characteristic vortical structures.

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