Unstart margin control of hypersonic inlets

The maximum performance of the hypersonic inlet/scramjet will be achieved when operating as close as possible to unstart boundary. In order to maintain the high performance without crossing the unstart boundary, an active unstart margin predictor and controller is necessary. The goal of the control system is to acquire the unstart margin and maintain the unstart margin as the designated value, and predict inlet unstart before it occurs, then take some measures to unstart mitigation or inlet restart. The unstart boundary and margin of hypersonic inlet were discussed and analyzed firstly. By analyzing the dynamic mechanism of the physical system, the dynamics of the hypersonic inlet can be regarded as unmodeled dynamics based on the frequency-domain simplification theory. The unstart boundary and margin reveal great nonlinear characteristic at different freestream conditions, so it is necessary to introduce the nonlinear control method to perform the control system design. The gain scheduling control method was introduced to compensate the nonlinear gain of the hypersonic inlet. To validate the validity of the controller, the simulation platform of CFD/MATLAB was established. The simulation results prove that the gain scheduling method is valid, and it can guarantee that the control system arrives at the same performance index at different freestream conditions.