Circumferential propagating characteristics of tip leakage flow oscillation and its induced rotating pressure wave

Abstract

The tip leakage flow oscillation and its circumferential propagation features are investigated numerically on a low-speed axial compressor rotor. Full-annulus unsteady simulations are performed at different operating conditions. The tip leakage flow oscillation is detected by the pressure fluctuation in the rotor tip region. The results show that the tip leakage flow has the same oscillating pattern in each passage, yet pressure fluctuations of neighboring passages have a phase lag, which can be modeled as a pressure wave propagating circumferentially relative to the rotor. This rotating pressure wave is considered mathematically using Fourier series. The results show that the rotating pressure wave induced by tip leakage flow oscillation contains multiple modes. A theoretical model is proposed to calculate the mode order, angular velocity and frequency of each mode. Finally, by comparing the calculated frequencies with both the predicted and measured pressure spectra, the theoretical model is demonstrated.