Numerical Study of Unsteady Self-Recirculating Casing Treatment in Micro Transonic Fan at Different Rotation Speed

This study investigates the regulation effect of a self-recirculating passive periodic excitation casing treatment on the stable operating range of a miniature transonic axial-flow fan rotor. Numerical simulations were conducted to analyze the performance impacts and internal flow mechanisms under different rotational speeds (70%, 80%, and 90% of the design speed). The results demonstrate that the self-recirculating casing treatment significantly enhances the rotor’s stall margin by modulating tip shockwave intensity, delaying leakage flow breakdown, and suppressing high-entropy regions. Specifically, the stall margin improvement reaches 7.11% at 70% design speed, while the enhancement diminishes progressively at higher speeds. This method effectively addresses the insufficient stall margin caused by the relatively large tip clearance ratio in miniature rotors, with only a minor efficiency penalty. The proposed strategy provides a feasible unsteady flow control solution for high-load design of miniature turbofan engines, offering critical insights into the interaction mechanisms between periodic excitation and tip leakage flow-shockwave dynamics.