Numerical investigation of the unstart flow at off-design condition of REST inlet at a Mach of 4

Unstart flow in a rectangular-to-elliptical shape-transition (REST) inlet at the off-design operating condition has been simulated using the detached eddy simulation (DES) method. With the help of numerical simulations, the development of the unsteady inlet unstart flow at the transitional condition is obtained. The evolution patterns of unstart flow as well as the characteristics at different stages are summarized. Also, the dynamic behavior of the separation bubble is investigated. Results indicate the dynamic behavior of the separation bubble is jointly dominated by the incoming flow, spillage and the backpressure/blockage ratio. The changes in downstream flow structures can break the balance between these factors and thus lead affect the separation bubble's movement. The mechanism of the bubble's direction switch is different according to its location. It is dominated by the increased back pressure/blockage ratio at the rearward position and the shear layer instability at the forefront position. The cowl-closure leading edge (CLE) and reflected CLE shock play an important role in this process, which jointly redistribute the turbulent pulsation. It accelerates the process of separated shear layer instability and downstream flow averaging, and simultaneously causes the change of separation bubble movement behavior.