Effects of increased tip clearance on the unsteady flow behaviors at near-stall condition in a counter-rotating axial flow compressor based on POD method

Abstract

To explore the effects of increased tip clearance on the unsteady flow behaviors at near-stall point (NSP) of a counter rotating axial flow compressor (CRAC) and its related physical mechanisms, this paper perform a deep comparative analysis of unsteady numerical simulation results of a two-stage CRAC at different tip clearance size (TCS), in combination with the Proper Orthogonal Decomposition (POD) method. From the results, it can be seen that the rear rotor (R2) leading edge (LE) has greater unsteady fluctuation intensity than the front rotor (R1) passage at different TCS. Potential flow interference from R2 causes higher static pressure fluctuations at R1 pressure surface (PS) and outlet than tip leakage flow (TLF). The unsteady fluctuation at the LE of R2 is more severe at large TCS. Frequency analysis indicates an increased frequency of TLF for R2. The POD analysis confirms the above conclusions and reveals the dominant structures and their influence range in the unsteady flow field at different TCS. Increased TCS leads to larger scale spillage structure at LE of R2, more complex mode composition, and higher energy contribution in the flow field.