Locked-in phenomenon between tip clearance flow instabilities and enforced blade motion in axial transonic compressor rotors

In this paper, tip clearance flow (TCF) instabilities and their relationship to blade motion are investigated numerically on a transonic transonic rotor with a large tip clearance. The numerical methods are verified by comparing with the experimental data of NACA0012 and show reliable results. It is found that the TCF instabilities are caused by the radial vortex formed in passage, which is induced by the interaction of tip clearance vortex (TCV) and main flow. When the blade is enforced vibrating with small amplitude, the results show that TCF instabilities are hardly affected by the blade vibration, and almost no phenomenon of locked-in is found. However, when the amplitude of blade vibration is increased, the interaction becomes stronger and the pressure fluctuation is enhanced. A wider locked-in region is observed. In addition, the simulation results show that the locked-in region is affected significantly by modal shapes. For the rotor here, it seems that the bending mode has a greater effect on the TCV instabilities than the torsional mode and causes a wider locked-in region. In locked-in region, the phase differences between TCV and the blade motion change with the flow conditions. In unlocked region, the period of TCF instabilities fluctuates over time, and the process is similar to that in the locked-in region.