Numerical Analysis of Flow Structures in the Tip Region of a Transonic Centrifugal Impeller

In this paper, the transonic centrifugal impeller with a pressure ration of 6.1 is choose as the study object. The unsteady characteristics of tip leakage vortex and the interaction between shock and tip leakage vortex in the tip region are investigated by steady and unsteady numerical simulation. The results shows that, the interaction between shock and tip leakage vortex becomes stronger as the mass flow rate decreases, and finally the tip leakage vortex breaks down. At small mass flow rate, the broken-downed tip leakage vortex induces the variation of blade loadings. In turn, the changed blade loadings will alter the intensity of tip leakage vortex. Such alternative behavior finally results in the periodic process. The single-passage numerical simulation shows that the oscillation frequency of unsteady flow is 0.668 BPF, and the two-passage and three-passage simulations indicate the oscillation frequency is 0.88 BPF, but the three numerical models shows the same unsteady flow mechanism.