Design and matching of flap-type variable camber stator in variable cycle engine

Variable cycle engine (VCE) can adjust its operational modes according to varying mission requirements, thereby achieving optimal performance across the entire flight envelope. A typical architecture employed in VCEs is the front/rear fan (FRFan) configuration. Removing the variable inlet guide vanes (VIGVs) of the rear fan and replacing the last-stage stator of the front fan with a variable camber stator (VCS) offers potential benefits in reducing axial length and weight of the compression system. While conventional arc-type VCSs are simple in structure and easy to adjust, their operation in adverse pressure gradient environments tends to introduce significant additional aerodynamic losses. To address this issue, a flap-type VCS was proposed in this study. By utilizing slot jet to energize the suction surface boundary layer, the flap-type VCS delayed boundary layer separation and substantially reduced aerodynamic loss. Numerical simulations were conducted to investigate the influence of the slot rear wall aspect ratio, offset ratio, and the geometric shape of the slot front wall on the aerodynamic performance of the flap-type VCS. An optimal design was identified based on the results. Comparative analyses showed that the flap-type VCS exhibited significantly lower total pressure loss and deviation angle than the arc-type design under the majority of operating conditions. Additionally, the flap-type slot helped to reduce the size of the shroud-corner separation, thereby improving bypass efficiency without shifting the matching operation point. By adjusting the flap-type VCS within a certain range (±10°), the FRFan operated across a bypass ratio range of 0.055 to 0.679. Specifically, the VCS contributed 22.92% and 29.33% to the expansion of the upper and lower limits of the bypass ratio, respectively. Theoretically, a zero-bypass-ratio condition could be achieved without additional actuation mechanisms through VCS adjustment.