Numerical investigation on short length-scale disturbance generation in an eccentric axial compressor rotor at a stable condition

Abstract Short length-scale disturbances have been found repeatedly in experiments on axial compressors with non-uniform tip clearance, and their flow field structure and relationship to stall inception have been closely followed by researchers. However, people's understanding has been constrained by experimental measurement techniques. In this paper, a new attempt to discern the short length scale disturbances with eccentric clearance has been made. The detailed flow field of an eccentric compressor is calculated for the first time utilizing the three-dimensional full annulus unsteady CFD method. The circumferential propagation of short-length disturbances occurred in the eccentric compressor rotor at the near-stall stable condition has been presented by this simulation. Work on this study has revealed for the first time by CFD that those disturbances only propagate at the position where local flow coefficient is low, and decay at the location where local flow coefficient is high, and the maximum amplitude of those disturbances occurs after the position of the maximum tip-clearance. The detailed flow field structures reveal that those disturbances are essentially moving radial vortices and the footprint of the 3D vortex system on the casing, which initiate from the separation at SS of the blade. Then get stronger and become radial vortices as they move toward the pressure side of the neighboring blade, and finally are broken down in the PS at the leading edge of the blade.