Numerical investigation of stall mechanism of an axial compressor at three different rotating speeds

For some axial flow compressors, the compressor stall is a result of the blade tip blockage caused by the complex flows, which include the boundary layer flow separation (BLFS), tip leakage flow (TLF), and shock wave. Owing to the difference of the design rotating speed and aerodynamic load in the axial flow compressor, these complex flows might exist in isolation or occur at the same time in practical application. Aiming at the stall mechanism in the axial flow compressors, a great deal of experimental and numerical investigations have been carried out at the design rotating speed. However, the investigation for off-design rotating speed in the axial flow compressors is seldom. Therefore, a transonic axial flow compressor rotor, which is NASA Rotor67, was chosen to investigate the stall mechanism at 100%, 80% and 60% design rotating speeds with the help of the numerical method. Moreover, the guiding suggestions for selecting the measures of increasing the transonic axial flow compressors stability are presented for the later investigation. The compared results show that the variation tendency of the experimental total performance lines are finely repeated by the numerical results at the three design rotating speeds. The fundamental flow mechanism of the rotor is obtained by analyzing the flow field in the blade passage in details. With the decrease of the rotor mass flow at the three design rotating speeds, the starting position of the tip leakage vortex (TLV) moves to the blade leading edge gradually, and the tip leakage vortex also deviates to the pressure surface of the adjacent blade. The deviated angle, which is the angle between the trajectory of the tip leakage vortex core and rotor rotating axis, for near stall point (NS) are about three degree, five degree and nine degree than that for near peak efficiency point (NPE) at 100%, 80% and 60% design rotating speeds respectively. The blockage resulted from the interaction between the tip leakage vortex and shock wave is the cause of the rotor stall at 100% and 80% design rotating speeds. Besides, the breakdown of the tip leakage vortex and leading edge spilled flow (LESF) occur at 80% design rotating speed. At 60% design rotating speed, the blockage caused by the leading edge spilled flow resulted from the tip leakage vortex is the main cause of bringing about the compressor stall, and the boundary layer flow separation (BLFS) in a small scope appears at the blade tip suction surface near the trailing edge.