An Experimental Investigation of the Non-Axisymmetric Casing Treatment for a Low-Speed Axial-Flow Compressor Under Circumferential Inflow Distortion

Aero-engine compressor often suffers from non-axisymmetric total pressure distorted inflow caused by S-duct or BLI inlets. Generally, the distorted inflow can reduce the stall margin (SM) of the compressor. In order to conquer this issue, casing treatment can be adopted for stall margin improvement (SMI). Considering that axisymmetric casing treatment always induces efficiency penalty, this paper conducted an experimental study on non-axisymmetric casing treatment (NACT) for a low-speed single-rotor axial compressor. Two type total pressure distortion inflow conditions including 30° and 60° annular range are involved. Also, various phase differences between NACT and distortion region are investigated. Experimental results indicate a 5.83% and 8.72% decrease in the compressor SM due to the two distorted inflow, respectively. At the near-stall point condition, the self-excited unsteadiness of tip leakage flow gradually intensifies after the rotor rotates into the distortion region, and it has a peak value at the exit of the distortion region where the first spike disturbance occurs. With the change in the phase difference, SMI obtained by NACT initially decreases, then increases, and finally exhibits a slight decrease. The maximum SMI values are 5.61% and 7.86% when the NACT extensively covers the exit of the distortion region for 30° and 60° distortion inflow conditions, respectively. Elaborate test of dynamic pressure and the wavelet analysis demonstrate that NACT can effectively suppress the initial stall disturbance with low-energy at the distortion region’s exit, preventing it from evolving into uncontrollable large-scale and high-energy stall cells. The analysis of the circumferential scale of stall inception indicates that the stall inception will occupy 7–8 blade passages after the application of NACT compared to SC of 2–4 blade passages under distorted inflow, which can provide some insights for future stall warning study.