Comparison of Vortex Identification Methods Based on the Liutex Decomposition and Application in a Compressor Cascade

Gaining a deeper insight into the complex vortex-dominated flow in aeroengine compressors is of great meaning for improving the aerodynamic performance of compressors. However, vortex regions vary depending on the vortex identification methods by which they are extracted. The Liutex based velocity gradient decomposition provides an effective approach to quantify the rigid-body rotation, pure shearing, and compression-stretching effects in fluid motion. The LT-plane constructed based on the local trace criterion provides a tool to geometrically represent the relationship of different vortex identifications. In this study, the commonly used Q series vortex criteria and the normalized Liutex method $${\tilde{\Omega }}_{L}$$ are analytically compared under zero threshold and non-zero threshold conditions. A typical corner separation flow in a highly loaded compressor cascade is analyzed. Vortex regions extracted by different vortex criteria with equivalent threshold values are compared. Results show that proper exclusion of pure shearing and compressing-stretching contamination helps to capture entangled vortex structures and indicate the pressure loss regions.