Supersonic inlet aerodynamic design and unstart analysis

For supersonic flight aircraft or missiles, a supersonic inlet is needed to slow down the flow speed with high efficiency and stability. A mixed compression inlet is often used for its high efficiency. However, a phenomenon called inlet "unstart" may occur when the flow field is disturbed by freestream or downstream component perturbation. The inlet unstart will expel the terminal shock wave to outside of the cowl entrance and will usually introduce sudden thrust loss and instability to the aircraft. We have developed a boundary conditions to simulate the boundary layer bleed to stabilize the terminal shock in the inlet. The unsteady supersonic inlet unstart mechanism due to angle of attack is analyzed by 3D CFD simulation. It is observed that the shock motion starts at the leeward side of the inlet. The terminal shock travels upstream and causes the flow separation, which rapidly spreads circumferentially and brings the entire inlet to unstart.

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