Study on the relationship between radial flow and rotating instability characteristics under different axial clearances

This study investigates the impact of axial gap variation on throughflow characteristics and rotating instability (RI) in axial-flow compressors, focusing on the relationship between radial secondary flow (RSF) and RI behavior. Full-annulus simulations of a 1.5-stage compressor are analyzed using proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) to extract dominant flow modes. Results show that higher-order modes in the tip region are dominated by frequencies linked to RI and leakage vortex/RSF interactions. The eigenfrequencies are governed by circumferential mode structures and propagation velocities. RSF exhibits consistent modal and frequency characteristics across radial positions. Increasing the axial gap reduces RSF energy and RI frequency energy, corresponding to weaker radial flow intensity and RI perturbations. DMD analysis confirms a positive correlation between RSF frequency and RI energy, highlighting the coupling mechanism. These findings provide new insight into the flow dynamics governing RI and offer guidance for compressor stability improvement.