Numerical simulation of unsteady tip clearance flow in a transonic compressor rotor

A three-dimensional, multi-passage unsteady numerical study was conducted to enhance the understanding of unsteady flow phenomena in the tip region of a transonic axial compressor rotor. Two different inlet conditions were applied to the transonic rotor to demonstrate the effect of the inlet condition on the unsteady flow phenomenon in the rotor tip region. The inlet conditions selected were axial inflow and 16-deg of co-swirl. The results show that different inlet conditions lead to different shock wave intensities and positions, which critically affects the unsteady flow structure in the tip region of the transonic rotor. Under the co-swirl inlet condition, the tip leakage vortex of each blade oscillates synchronously at the near stall point because of the weak interaction between the tip leakage vortex and the shock. Under the axial inlet condition, the rotating instability phenomenon appears as the “multi-passage structure,” which propagates along the circumference occurring at the tip of the rotor in the stable operating range due to the strong interaction between the tip leakage vortex and the shock wave. With the decrease of the mass flow, the mode order of the “multi-passage structure” does not change, but the fluctuation frequency decreases gradually.