Axial Slot Casing Treatment To Improve The Stall Margin Under Circumferential Total Pressure Distortion On An Axial Flow Compressor

As a typical stability enhancement method, the axial slot casing treatment (ASCT) has been verified to extend the stall margin under uniform inflow condition. In order to further investigate its stability-enhancing capability under distorted inlet conditions, a series of experimental studies were carried out on a low-speed axial flow compressor. An ASCT structure which can improve the stall margin by 38.75% under uniform inflow was studied. Three types of circumferential total pressure distortion intensities, namely, 0.90%, 4.12%, and 24.75%, are selected to conduct the steady and unsteady measurements with and without ASCT. The results showed that the three distorted inflow have deteriorated the compressor stall margin by 7.87%, 9.19% and 39.08%, respectively. The ASCT can widen the compressor stall margin by 43.86%, 40.27%, and 22.83% under the three distorted inflow conditions, respectively. It demonstrates the strong anti-distortion capability of ASCT. The unsteady pressure signal measured on the casing wall showed that the ASCT could significantly reduce the circumferential propagation speed of stall precursors under all inflow conditions. Under the circumferential total distorted inflows, the stall precursor first appears at the position where the rotor is about to rotate out of the distortion region, and then decays in the undistorted region. The power spectral density of the stall process showed that the ASCT can suppress the disturbance, whose frequency is near the rotating stall frequency band, thereby delaying the occurrence of rotating stall.