Unstable flow characteristics in vaneless region with emphasis on the rotor-stator interaction for a pump turbine at pump mode using large runner blade lean

Abstract

In this study, the unstable flow characteristics in vaneless region of the pump-turbine with different runner blade lean has been numerically investigated by using a modified SST k-ω partially averaged Navier-Stokes model. Results on the characteristic curves show good agreements between the experiment and simulation, and indicate that with the increase of blade lean angle (θ of 0°, 2°, 4°, 6°, 10° and 15°), the positive slope on characteristic curve is gradually alleviated. It is noted that the runner with large blade lean (θ of 15°) can suppress the peak value region of boundary vorticity flux at blade trailing edge from the crown side to mid-span section, and the unstable flow near the mid-span in runner blade-to-blade passage as well as in vaneless region. It is confirmed that the runner with large blade lean spatially and temporally changes the flow near the blade trailing edge and in vaneless region, and is beneficial to improve the flow stability. Finally, the proper orthogonal decomposition analysis reveals that the runner model with large blade lean effectively alleviates the dominant flow oscillation with the low frequency of 0.088fn (or 0.044fn), corresponding to the unstable flow evolution in vaneless region.