Abstract
Positive slope characteristics are very important for the safe and stable operation of a pump-turbine. In this study, the unsteady flows in a pump-turbine at pump mode are investigated numerically. To predict the positive slope characteristics with an improved accuracy, a modified Partially-Averaged Navier-Stokes (MPANS) model is employed to capture the unstable physics in a pump-turbine. It is confirmed that the present numerical method predicts the positive slope characteristics in the pump-turbine fairly well compared with the experimental data. It is noted that at the drooping point of the performance curve (positive slope), there are three sets of rotating stall cells in the flow passages of both the guide vanes and stay vanes. In the guide vane region, the flow is completely shut off by the rotating stall, whereas in the stay vane region, the flow passage is partly blocked at the drooping point. The numerical results also reveal that the remarkable variation and high angle of attack (AOA) values upstream the leading edge of the guide vane contribute to the flow separation at the vane suction side and induce rotating stall in the flow passage within the positive slope region. Furthermore, the propagation of the rotating stall is depicted by both Eulerian and Lagrangian viewpoints: the rotating stall blocks the flow passage between two neighboring guide vanes and pushes the flow toward the leading edge of the subsequent guide vane. The rotating stall cell shifts along the rotational direction with a much lower frequency (0.146fn) compared with the runner rotational frequency, fn.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
Widmer C, Staubli T, Ledergerber N. Unstable characteristics and rotating stall in turbine brake operation of pump-turbines. J Fluids Eng, 2011, 133: 041101
Sinha M, Pinarbasi A, Katz J. The flow structure during onset and developed states of rotating stall within a vaned diffuser of a centrifugal pump. J Fluids Eng, 2001, 123: 490–499
Luo X W, Ji B, Tsujimoto Y. A review of cavitation in hydraulic machinery. J Hydrodyn Ser B, 2016, 28: 335–358
Ciocan G D, Kueny J L, Mesquita A A. Steady and unsteady flow pattern between stay and guide vanes in a pump-turbine. In: Cabrera E, Espert V, Martínez F, eds. Hydraul Machinery Cavitation. Dordrecht: Springer, 1996. 381–390
Ciocan G D, Kueny J L. Experimental analysis of the rotor-stator interaction in a pump-turbine. In: Proceedings of the Iahr Symposium. Yokohama, 2006. 216–226
Ran H J, Luo X W, Zhu L, et al. Experimental study of the pressure fluctuations in a pump turbine at large partial flow conditions. Chin J Mech Eng, 2012, 25: 1205–1209
Lu G C, Zuo Z G, Sun Y K, et al. Experimental evidence of cavitation influences on the positive slope on the pump performance curve of a low specific speed model pump-turbine. Renew Energy, 2017, 113: 1539–1550
Braun O, Kueny J L, Avellan F. Numerical analysis of flow phenomena related to the unstable energy-discharge characteristic of a pump-turbine in pump mode. In: ASME 2005 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2005. 1075–1080
Ran H J, Luo X W, Zhang Y, et al. Numerical simulation of the unsteady flow in a high-head pump turbine and the runner improvement. In: ASME 2008 Fluids Engineering Division Summer Meeting Collocated with the Heat Transfer, Energy Sustainability, and, Energy Nanotechnology Conferences, 2008. 1115–1123
Liu J T, Liu S H, Wu Y L, et al. Numerical investigation of the hump characteristic of a pump-turbine based on an improved cavitation model. Comput Fluids, 2012, 68: 105–111
Sun Y K, Zuo Z G, Liu S H, et al. Numerical study of pressure fluctuations in different guide vanes’ opening angle in pump mode of a pump turbine. IOP Conf Ser-Earth Environ Sci, 2012, 15: 062037
Sun Y K, Zuo Z G, Liu S H, et al. Distribution of pressure fluctuations in a prototype pump turbine at pump mode. Adv Mech Eng, 2014, 6: 923937
Guo L, Liu J T, Wang L Q, et al. Pressure fluctuation propagation of a pump turbine at pump mode under low head condition. Sci China Tech Sci, 2014, 57: 811–818
Pacot O. Large Scale Computation of the rotating stall in a pumpturbine using an overset finite element large eddy simulation numerical code. Doctoral Dissertation. Switzerland: École polytechnique fédérale de Lausanne, 2014
Girimaji S S. Partially-averaged Navier-Stokes model for turbulence: A reynolds-averaged Navier-Stokes to direct numerical simulation bridging method. J Appl Mech, 2006, 73: 413–421
Girimaji S S. Abdol-Hamid K. Partially-averaged Navier Stokes model for turbulence: Implementation and validation. In: 43rd AIAA Aerospace Sciences Meeting and Exhibit-Meeting Papers. Reno, 2005
Huang R F, Luo X W, Ji B, et al. Turbulent flows over a backward facing step simulated using a modified partially averaged Navier- Stokes model. J Fluids Eng, 2017, 139: 044501
Shadden S C, Lekien F, Marsden J E. Definition and properties of Lagrangian coherent structures from finite-time Lyapunov exponents in two-dimensional aperiodic flows. Physica D, 2005, 212: 271–304
Cheng H Y, Long X P, Ji B, et al. Numerical investigation of unsteady cavitating turbulent flows around twisted hydrofoil from the Lagrangian viewpoint. J Hydrodyn Ser B, 2016, 28: 709–712
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Yang, D., Luo, X., Liu, D. et al. Unstable flow characteristics in a pump-turbine simulated by a modified Partially-Averaged Navier-Stokes method. Sci. China Technol. Sci. 62, 406–416 (2019). https://doi.org/10.1007/s11431-017-9259-3
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11431-017-9259-3