Quantitative evaluation of the unsteady behaviors of the tip leakage vortex in a subsonic axial compressor rotor

Tip leakage flow is inherently an unsteady flow phenomenon, which plays an important role in compressor stability. A quantitative evaluation of the unsteady behaviors of tip leakage vortex will help reveal the effect of tip leakage flow on the compressor characteristics. In this paper, stereoscopic particle image velocimetry (SPIV) is used to investigate the unsteady behaviors of tip leakage vortex near the rotor tip region in a low-speed axial compressor test facility. By using a vortex identification method, the size, location, the number and some other parameters of the TLV in the instantaneous realizations of the SPIV results are extracted. Based on the statistical analyses of these critical parameters, the unsteady behaviors of the TLV (vortex wandering, vortex splitting, and vortex breakdown) are quantitatively evaluated. A parameter is defined to quantitatively evaluate the intensity of the tip leakage vortex wandering, and it is found that the intensity of vortex wandering increases slowly at first but then increases rapidly as the TLV propagates downstream. Vortex splitting is found to start at different streamwise locations for different mass flow rate conditions, and from the initial position of the vortex splitting the average number of TLV increases with the streamwise location. The backflow induced by the vortex breakdown in the tip leakage flow is significant in the SPIV results. At last, the effect of the TLV's wandering, splitting, and breakdown on the evolution of the blockage is also discussed. (C) 2016 Elsevier Inc. All rights reserved.