Numerical Investigation of the Outlet Stage Variable Tandem Stator Adjustment on the Performance and Internal Flow Mechanism in an Ultra-Wide Range Adjustable Fan

Abstract With the continuous expansion of the aero engine flight envelope, the three-bypass adaptive cycle compression system must enhance both the flow adjustment range of the rear fan and the throughflow capacity during high Mach number flights. This study introduces a variable tandem stator configuration as a novel approach to address these two critical challenges. Through numerical simulations, this research investigates the impact of adjusting the stagger angles of the front and rear blades of the tandem stator on the performance and internal flow field of the front and rear fans at 80% corrected speed. The results show that under the constraint of the internal bypass design pressure ratio, adjusting the rear blade stagger angle can increase the total fan flow by 4.06%, with the flow adjustment range of the rear fan exceeding 13.73%. In this case, the flow adjustment of the rear fan is predominantly influenced by the inlet pre-swirl. The limitation on further reducing the rear fan flow stems from the stall occurring at the tip of the first-stage rotor blade of the front fan. Adjusting the front blade stagger angle can increase the total fan flow by 2.86%, with the flow adjustment range of the rear fan exceeding 13.04%. Unlike adjustments to the rear blade stagger angle, changes in rear fan flow are determined by the matching characteristics between the front and rear fans. When the front blade stagger angle is decreased to −10 deg, fan instability transitions from the first-stage rotor tip blockage to corner stall at the root of the second-stage stator. Coordinated adjustment of the front and rear blades can further enhance the throughflow capacity of the front fan and broaden the flow adjustment range of the rear fan while improving the working efficiency. The results hope to guide in the wide range flow adjustment of variable cycle engines and the design of variable tandem stators.