Numerical investigation on unsteady characteristics of tip leakage vortex of transonic compressor rotor

In order to study the unsteady characteristics of tip leakage vortex in a single compressor rotor system, a series of unsteady simulations of Rotor 67 were carried out at different back pressures and rotating speeds. The results showed that there was an unsteadiness boundary for each characteristic curve, which was divided into two parts, steady and unsteady. When the rotor operated at unsteady part, the increase of back pressure led to the decrease of frequency of tip leakage vortex. This was attributable to the decrease of tip blade loading near leading edge, finally bringing about the decrease of driving power of tip leakage vortex inception. The frequency of tip leakage vortex was related to the rotating speed of rotor. When the rotating speed was high, the tip leakage vortex showed lower frequency. When the rotating speed was low, the tip leakage vortex showed higher frequency. This was attributable to the detached degree of detached shock wave which was related to the rotating speed, leading to the differences of excitation positions where shock wave stimulated tip leakage vortex. At any rotating speed, there was a strong regularity of circumferential velocity of pressure wave induced by tip leakage vortex. With the decrease of massflow factor, the wave velocity decreased. And the decreasing rates were almost the same at any rotating speeds. In addition, the initial points of unsteadiness at every rotating speed almost stood in a straight line.