Numerical and Experimental Investigation on the Effects of Inlet Swirl Distortion on a Low Speed Axial Compressor

Inlet swirl distortion will degrade compressor performance and aerodynamic stability. In order to investigate its mechanism, a blade type swirl distortion generator was designed, which is competent to produce both of the twin swirl and bulk swirl. Experiment was carried out using this swirl generator. A twin swirl case was simulated numerically using steady-state and unsteady calculation methods, respectively. The results show that bulk swirl may not have the same effect as pre-swirl inlet condition, since the center of the vortex is not on the axis of rotation, causing more complicated results. All forms of the swirl will decrease the total pressure ratio and efficiency, but have different influences on the stall margin and stable region, which is analyzed in detail. Under the settings of the experiment, the co-rotating part of the twin swirl has a small impact on the compressor, and that of the counter-rotating part is strong, which causes suction surface boundary layer separation of some of the blade roots. This is the reason for the reduction of the aerodynamic stability of the compressor. The stall margins given by the steady-state and unsteady-state solutions differ significantly, and the unsteady results are closer to the experimental results. The main reason causing compressor instability is also analyzed in detail through numerical simulation. The findings of this study are novel and may provide a new perspective into the mechanism of swirl distortion effects.