Analysis on the Mechanism of Rotating Stall Inner a Pump Turbine in Pump Mode Based on the Proper Orthogonal Decomposition

An in-depth understanding of stall behavior is essential to improve the safe and stable operation of the pump turbine. In this research, the detached eddy simulation (DES) is used to investigate the various characteristics and propagation mechanism of the rotating stall of the hump instability region. The frequency characteristics and spatial intensity distribution of the stall cells are studied by adopting the proper orthogonal decomposition (POD) method. The results indicate that the energy loss at 0.80Q(DES) and 0.75Q(DES) are induced by the rotating stall with three cells that occur in the diffuser flow channel, and the corresponding high amplitude frequencies are St(0.0074) and St(0.0111), respectively. The effect of the stall cells is particularly severe near the hub. When the flow rate is further reduced to 0.68Q(DES), the three rotating stall cells develop into two symmetrically distributed stable stall cells with no definite characteristic frequencies, and the blocking phenomenon is concentrated near the shroud. With the stall cells losing their rotational characteristics, they have less impact on the flow field and contribute less energy. This paper also reveals that the energy loss in the diffuser contributes significantly to the hump formation on the performance curve.