Prestall Disturbances and Stall Inception for an Eccentric Low-Speed Axial Compressor with Inlet Swirl

Owing to the manufacturing and assembly error or the fatigue of long-time operation, nonaxisymrnetric tip clearance is actually a common phenomenon in compressors. It is also well accepted that tip leakage flow, associated with tip clearance size and loading, has a strong influence on the performance and stall inception of compressors. The work of this paper, based on an eccentric compressor with/without inlet swirl distortion, is aimed at strengthening the understanding of stall inception for a real geometry compressor experimentally. Results indicate that rotor tip blockage and flow unsteadiness vary evidently around the circumference. For this compressor, the maximum tip flow unsteadiness and blockage happens at the location near the minimum clearance under the condition of clean inlet flow. Before the occurrence of stall inception, disturbances arise and vanish intermittently within the region of high unsteadiness. However, it fails to rotate due to the inhibition of the low unsteadiness region. Once the most robust region is no longer able to suppress disturbances, stability finally breaks down and stall inception generates. After exerting inlet paired swirl, unsteadiness within the region of positive preswirl decreases significantly and the maximum unsteadiness location shifts, while the increase for the region with negative preswirl is nearly negligible. As a result, stall margin of the compressor is improved.