Experimental investigation of characteristics and influence of tip leakage vortex wandering in an axial compressor cascade

Vortex wandering is one of the most basic unsteady flow characteristics of the tip leakage vortex (TLV) in compressors. In this study, stereo particle image velocimetry (stereo-PIV) has been conducted in compressor cascades with various tip clearances to investigate the characteristics and influence of TLV wandering. The most effective vortex identification method for stereo-PIV data has been clarified. The wandering characteristics of the TLV are statistically analyzed, and the relationship between the vortex wandering and the dominant proper orthogonal decomposition mode is identified. The results reveal that TLV preferentially wanders along the pitchwise direction in the blade channel and gradually loses the dominant wandering direction downstream of the blade. The large displacement of the vortex center around its mean location is characterized by higher probabilities at small tip clearance size (1% chord length C). The spatial distribution characteristics demonstrate similarly concentric isocontour around the mean vortex center location for large tip clearances (3% and 5% chord length C). The effect of TLV wandering on the secondary velocity distribution, the tip flow blockage, and the distribution of Reynolds stress is explored using the vortex wandering corrected technique. The analysis verifies that the elevated turbulence kinetic energy in the core of the time-averaged uncorrected TLV is caused by vortex wandering rather than vortex deformation. The discussions of the current paper will enhance our knowledge of TLV wandering. Regardless of the reference to TLV, the interpretation of other swirling flows can benefit from the discussions presented here.