Experimental Investigation of the Influence of Inlet Distortion on the Stall Inception in a Low Speed Axial Compressor

Abstract

Inlet distortion is one of the major concerns for high maneuverability airplanes. An experiment is performed to investigate the influence of inlet distortion on the stall inception in a low speed axial compressor, where the distorted inlet flow field is simulated with a flat baffle placed upstream of the compressor. The flow field around a rotor blade is measured using 2D Digital Particle Image Velocimetry (DPIV) under both uniform and distorted inlet flow conditions. A comparison of flow fields reveals that the distorted inlet flow condition makes the compressor flow fields asymmetric. Flow separation and blockage within Distorted Sector A and Transition Sector B are more severe compared to Sector C. The distorted Sector A and Transition Sector B are the key regions that degrade compressor performance and stability. The large axial velocity makes the flow field within the Undistorted Sector C vigorous, which helps to suppress flow separation and blockage. Compressor rotor blades experience loading and unloading in a revolution period and the compressor exhibits strong dynamic response when it operates under distorted inlet flow conditions. Time-related pressure signals acquired at the rotor exit are utilized to analyze the development of the stall disturbance and the stall characteristic of the compressor. The development period of the stall disturbance is prolonged by the dynamic response of the compressor flow field under the distorted inlet flow condition. Dynamic development of the stall disturbance induced by inlet distortion reduces the compressor stall intensity. The frequency associated with the rotating stall cell is related to the rotating velocity of stall cells, which keeps the same value for uniform and distorted inlet flow conditions. Consequently, the stall inception of the compressor is influenced by the distorted inlet flow condition. The disturbance initiated in Distorted Sector A will experience development and damping when it propagates circumferentially, and might fail to survive the damping within Undistorted Sector C. Stall inception occurs only when the damping within Undistorted Sector C is insufficient to prevent its growth. The dynamic development of the disturbance can reasonably explain the influence of inlet distortion on compressor performance.