排气扩压器对高空舱压的影响与控制方法

为研究排气扩压器流动特性对高空舱后舱压力控制的影响,采用ANSYS191对排气扩压器进行数学建模和流场数值模拟分析,揭示其内部实际流动的物理过程;在次流质量流量为20 kg/s时,数值模拟不同排气扩压器背压和主流流量时后舱压力的变化规律,并通过样条插值得到排气扩压器背压、主流流量和后舱压力三者关系模型;建立高空舱后舱压力控制系统仿真模型,分析在不同调节模式和不同控制方法下排气扩压器流动特性对压力调节的影响。结果表明:发动机喷嘴出口处速度最大,混合后速度迅速下降,下降了约88%,而压力沿着排气扩压器轴向逐渐增大,最后趋于边界值。在发动机过渡态试验中,排气扩压器流动特性对后舱压力控制系统扰动很大,线性PID(proportion integration differentiation)控制难以保证后舱压力高精度、强抗扰的调节品质要求,而非线性PID控制不仅能减小排气扩压器流动特性对压力调节的影响,抑制发动机流量扰动,而且能保证瞬态响应快,超调量小,调节精度高。 

Influences of exhaust diffuser on chamber pressure and control method for high altitude cell

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.