Unsteady near-stall flow mechanisms in a transonic compressor rotor at different rotating speeds

Abstract

Since aero engines have to ensure aerodynamic stability within the full rotating speed range, the exploration of near-stall flow characteristics at different rotating speeds will lay a foundation for the next step of adopting reasonable casing treatment methods. In this paper, unsteady numerical simulations were conducted for a transonic rotor to investigate near-stall flow mechanisms and unsteady characteristics at 100% and 80% rotating speeds, and simulation method was well-validated with experimental data to ensure that the critical flow characteristics at the near-stall conditions were captured accurately. The result of research shows that the tip blockage comes into being downstream the interaction between tip leakage vortex and shock wave, which hinders the flow entering the rotor passage. At 80% speed, as opposed to 100% speed, the weaker but more upstream shock wave results in the blockage closer to the leading edge at the near-stall condition, which gives rise to more frequent and fierce unsteady activities. The evolution processes of vortex structure and relevant blockage distribution are elucidated by vortex identification and quantification of blockage area in oscillation periods for both rotating speeds. The vortex structure resulting from the breakdown of the tip leakage vortex emerges at the inlet near the pressure side, and then moves downstream and inward radially. By the time the vortex structure is about to exit the rotor passage, a newborn vortex structure has come being at the inlet. The development of vortex structure in one oscillation period gives rise to the periodic variation of blockage throughout the entire rotor passage.