Evolution of Pressure Signature Dominated by Unsteady Tip Leakage Flow

This paper deals with the detailed numerical analyses of diverse manifestations of unsteady features induced by periodical oscillation of tip leakage flow under different operating points for the cases with uniform and hub distorted inlet conditions. The characteristics evolutions of pressure signature near rotor tip region during compressor throttling process are studied and compared with the experimental results. Monitors circumferentially arranged and aligned with blade chord are imposed to collect static pressure signals. Analysis methods of coordinate transformation between the rotor relative and absolute stationary reference frames, fast Fourier transform and frequency band pass filter are used. The modulated frequency features along blade chord in two reference frames are analyzed. Typically for the dominated frequency components, the circumferential propagation characteristics are studied, such as propagation speed and mode orders. And the unified evolution trends of modulated frequency relation for dominant components between two reference frames and circumferential propagation features during throttling process are summarized. A critical mass flow point is found to distinguish the different change trend of the characteristics of tip leakage flow unsteadiness. Based on the different speeds between circumferential propagation of tip leakage flow unsteadiness and revolution of compressor rotor, the fluid dynamic reason for the decrease of autocorrelation coefficient of pressure signals from transducer mounted on compressor casing is elucidated. All the results are helpful to further unveil the initiation mechanism of stall inception.