In order to study the influences of flow characteristics of exhaust diffuser on the rear chamber pressure control of altitude test facilities

the flow characteristics of exhaust diffuser were analyzed and the model was constructed by ANSYS191 to reveal the true physical process. When the secondary mass flow rate was 20 kg/s

the changes of the rear chamber pressure were numerically simulated under different exhaust diffuser back pressure and main flow rate

and the model of the back pressure of exhaust diffuser

main flow rate and rear chamber pressure was obtained by spline interpolation. A simulation model of the pressure control system of rear chamber of high altitude platform was established to analyze the influences of the flow characteristics of the exhaust diffuser on the pressure regulation under different regulation modes and different control methods. The results showed that the secondary flow had great influences on the primary flow

and the velocity reached maximum at the engine nozzle exit. Then the velocity decreased quickly and declined by 88% in the mixing section of exhaust diffuser. However

the pressure increased gradually to the boundary value along axial direction of exhaust diffuser. In engine transition tests

the flow characteristics of exhaust diffuser brought great disturbances to the rear chamber pressure control system

and the regulating precision and disturbance rejection of rear chamber pressure can’t be assured by linear PID controller. However

nonlinear PID control can not only reduce the influence of the exhaust diffuser flow characteristics on the pressure regulating and reject the engine flow disturbances

but also ensure that the transient response is fast

the overshoot is small and the regulation accuracy is high.