On the Mechanism of Rotating Stall in a Boundary Layer Ingesting Fan

Abstract

Next-generation boundary layer ingesting (BLI) aircraft can achieve significant reductions in fuel burns compared to conventional aircraft. One of the challenges for BLI aircraft is the need for the fan to continuously operate with inlet distortions. However, until now the effect of real BLI distortions on rotating stall remains unclear. In this work, full-annulus unsteady simulations are conducted to analyze the mechanism of rotating stalls in a boundary layer ingesting fan. The complete stall hysteresis loop at BLI distortions is investigated. Similar to the uniform inflow, the fan at the BLI distortions also exhibits the spike-type rotating stalls, and its stall inception is also attributed to the radial vortex structure caused by the shear interaction between the incoming flow and backflow. However, at the BLI distortions, the evolution process of rotating stall is accompanied by the growth and decay of disturbances because of the significant variation of the inflow condition around the whole annulus. Only when the stall disturbance becomes large enough can it propagate circumferentially across the whole annulus to form the full stall cell. In addition, due to the significant decrease in total pressure ratio, the fan at the BLI distortions is easier to exit the rotating stall compared to the uniform inflow. These results enhance the understanding of the rotating stall mechanism not only for BLI fans but also for many turbine engines that suffer from inlet distortions.