Modeling and control law design of ramjet engine for supercritical operation

Abstract

A dynamic model for ramjet engine having variable nozzle is developed and its control law is designed for supercritical operation considering model uncertainty and air disturbances. The dynamic model of engine is subdivided into several sections to capture the dominant physical phenomenon such as supersonic, subsonic cold gas flow and combustor hot gas flows and is assembled by connecting separate sections with connecting gas dynamic variables. To control the supersonic intake, the terminal shock position is selected as model output about the variable nozzle throat input. The model accuracy is compared with the engine performance results which are verified through CFD simulation for different altitude, Mach number and control inputs. An air disturbance model suggested by Tank and downstream disturbance are quantified to obtained uncontrollable supercritical margin considering nozzle actuator dynamics. To measure the allowable position of terminal shock, sensitivity equation is induced and combined with the quantified disturbance. Nonlinear adaptive backstepping scheme is applied to obtain robust and simple control law under the model uncertainties which is induced from model reduction. The stability of controller is induced from Lyapunov based theory and the performance and stability of controller is verified through several numerical simulations by combining independent disturbances.