Investigation of the flow field interference mechanism and broadening of the mass flow stability boundary in a front-blade-variable tandem blade

To meet the wide operating range requirements of compression systems in variable-cycle engines, enhanced adaptability to varying mass flow rates is essential. Tandem blades provide a potential solution to this demand by functionally decoupling flow adaptation and flow turning between the front blade (FB) and the aft blade (AB). This paper investigates tandem blades with a variable FB. A collaborative optimization design method suited for broadening the operating range of variable tandem blades is proposed, and this method is used to explore the influence of the axial overlap (AO) and the percent pitch (PP) on the mass flow adaptability range. The optimized result yields AO = −0.13 and PP = 0.99, which differs markedly from the conventionally accepted range for fixed tandem blades. Under the constraint of a total pressure loss coefficient ≤0.07, the mass flow adaptability range is broadened by 7.56%, and the corresponding attainable inflow angle range is expanded from 21.8° to 25.7°, with the FB stagger angle adjustment range extended by 3°. Further flow mechanism analysis reveals that, at the high mass flow boundary condition, the optimized blade virtually eliminates the axial gap between the FB and the AB, thereby reducing the local negative incidence angle at the AB leading edge and suppressing separation on the AB pressure surface, which constitutes the fundamental reason for the broadened mass flow adaptability range.