Passive control of flow separation with blade-end slots for a three-stage compressor at different Reynolds numbers

The unmanned aerial vehicles (UAVs) operate at flight altitudes exceeding 20 kilometers, where the effect of low Reynolds number ($\text{Re}$) on the aero-engine of UAVs is significant. The blade-end slots technique is proved to be an effective method to control the corner separation flow in the blade end regions under conventional Reynolds number. To verify the effectiveness of this technique under low $\text{Re}$ conditions, the blade-end slots technique is applied to a three-stage compressor under high flight altitude conditions. The control effect and mechanism of the blade-end slots under different $\text{Re}$ are revealed to lay a foundation for the subsequent experiments of the three-stage compressor at low $\text{Re}$ condition. Results show that the loss near the blade-end region under 20 km (low $\text{Re}$) condition is larger than that under 0 km (high $\text{Re}$) condition. The employment of the blade-end slots technique can significantly suppress the corner separation and widen the stall margin of the three-stage compressor without reducing the efficiency. The self-adaptive jet generated by blade-end slots effectively displaces low-momentum fluid near the suction surface and restricts its spanwise migration along the blade. Furthermore, the single blade-end slotted scheme for the third-stage stator and the combined blade-end slotted scheme for each stator can increase the stall margin by 3.52% and 6.81% under 20 km condition, respectively. These findings underscore the potential of blade-end slots as a control mechanism to optimize compressor performance under low $\text{Re}$ conditions.