Effects of injection frequency on the rotor stall margin

The stall margin of compressor could be improved effectively by rotor tip injection, and the periodic injection is commonly used in the research. The purpose of this work is to investigate the influence of injection frequency on the rotor stall margin. An unsteady CFD code was employed to simulate the flow field of the rotor with injections of different frequencies. Comparing the stall margin of the rotor with injections of different frequencies, it is shown that there is an optimal injection frequency, around which the rotor stability enhancement is the largest. When the injection frequency is away form the optimal frequency, the improvement in stable flow range decreases correspondingly. For the rotor in this paper, the optimal frequency was 1.5 times the frequency of tip leakage vortex (for short, TLV) fluctuation. Time-averaged loading distribution at 98.5% span indicates that the loading of the rotor near the leading edge is decreased through injection with the optimal frequency, and therefore, the stall could be delayed.