Variable tandem stator geometric features on fan performance

To meet the requirements over a broad flight envelope, the rear fan of the three bypass variable cycle engine requires extensive flow adjustment. This study proposes a variable tandem stator configuration for the front fan outlet stage. Our research investigates the geometric features, including the hub clearance size, hub rotation, and the rear blade (RB) stagger angle, and their effects on both the front fan performance and internal flow. Numerical results show that the introduction of hub clearance has a negligible effect on the total pressure ratio and isentropic efficiency of the fan. The maximum stall margin, which is 21.73% greater than the prototype, is achieved with a 1%τ clearance. Flow field analysis shows that corner stall at the front blade evolves into corner separation, thus delaying the onset of the corner stall. Hub rotation enhances the fan stall margin by 16.81%. Additionally, it introduces secondary leakage in the clearances that does not cause new mixing losses. Instead, it mitigates the blockage across all blade heights, reducing flow losses. Changing the rear blade stagger angle has minimal effect on stall margin. Additionally, adjusting it in the negative direction increases the maximum pressure ratio while decreasing peak efficiency. Adjusting it in the positive direction has the opposite effect due to the load changes caused by the stator camber angle adjustment. Loss analysis shows that load changes primarily influence the magnitude and proportion of secondary flow losses and wake losses. The results hope to guide in the wide range flow adjustment of variable cycle engines and the design of variable tandem stators.