Effects of speed ratio and flow rate on stall cell flow pattern and propagation in a counter-rotating axial compressor

As an instability phenomenon observed in compressors, fans, and pumps at low flow rates, rotating stall can lead to decreased compressor performance, induce surge, and even cause fatigue failure of blades. The paper presents experimental and numerical studies on the three-dimensional stall flow pattern and the propagation mechanism of stall cells in a low-speed counter-rotating axial compressor. The results show that the types of stall precursors in the counter-rotating compressor are related to rotor speed ratio. At low speed ratios, spike-type stall disturbances with individual small stall cell were observed, while at higher speed ratios, it appeared as small-scale disturbances with multiple stall cells. In the fully developed stall condition, the flow pattern of rotating stall remains basically uniform under different speed ratios and flow rates, with the main difference being the propagation velocity of the stall cell. Based on these findings, a simplified model for the propagation of stall cells in counter-rotating compressors has been established. For a fully developed stall flow field, it was determined that the propagation of stall cell is essentially a global behavior of the flow field closely related to torque matching between two rows of rotor blades. Finally, the propagation speed of the stall cell under different speed ratios and flow conditions was predicted, and the reliability of the model was verified using experimental results.