Numerical investigations of HSCT inlet unstart transient at angle of attack

The unstart transient of a High Speed Civil Transport (HSCT) mixed compression axisymmetric inlet at Mach 2 and 2° angle of attack was investigated numerically by using a 3D time accurate Navier- Stokes solver. The Baldwin-Lomax algebraic turbulence model and an extrapolation uniform mass bleed boundary condition for the slot bleed were employed. It is observed that, when an angle of attack is imposed, the flow on the leeward side has a stronger compression than that at zero angle of attack. The strong compression reduces the Mach number upstream of the terminal shock and therefore makes the shock move upstream first on the leeward side. The initial shock motion starts with the bifurcation of the terminal shock. The lower part of the split shock is stable due to the centerbody bleed while the top part of the shock continues to travel upstream. When the terminal shock on the leeward side passes the bleed region, a separation is induced by the shock/boundary layer interaction on the shoulder of the inlet centerbody and the entire inlet is brought to unstart. The overall computed flow field phenomena agree qualitatively with the experimental observations.