Stall mechanisms of a transonic compressor rotor with axisymmetric and nonaxisymmetric tip clearance layouts

This study employs full-annulus unsteady simulations to explore the unsteady tip flow and stall mechanisms in a transonic compressor with axisymmetric (ASY) and nonaxisymmetric (NASY) tip clearance layouts. The investigation highlights the impact of second-harmonic clearance distributions, caused by casing ovalization, on aerodynamic stability and stall behavior. While the stall inception from near stall to stall conditions shows similar characteristics (spike-type inception) for both layouts, the NASY layout results in distinct stall mechanisms. A second-harmonic axial momentum distribution of tip leakage flow is observed before stall onset, aligned with the clearance distribution. After stall onset, this pattern deteriorates, particularly in regions with increasing clearance, where enhanced axial momentum and faster stall cell propagation (approximately 75% of the rotational speed) are observed. In contrast, sectors with decreasing clearance exhibit weaker stall intensity and propagation speed comparable to the ASY layout (62.5% of the rotational speed). These dynamics reduce the stall margin of the transonic compressor with NASY clearances. A circumferential stall cell propagation model is developed, capturing the distinct propagation characteristics in NASY layouts. This study emphasizes the necessity of accounting for nonaxisymmetric clearance effects in modeling and predicting compressor stall behavior and stability.