Dynamic Modeling And Control Method Of High Speed Wind Tunnel

Wind tunnel plays a crucial role in the experimental basis for the development of aircraft in the field of aerospace.Its appearance greatly reduces the development cycle and cost of aircraft.With the improvement of wind tunnel,the upgrade of aircraft is often brought.The wind tunnel developed from the traditional linear fan type to the return type wind tunnel,and then to the faster transient wind tunnel.Now there are burning wind tunnels that can reach hypersonic speeds.The continuous development of wind tunnel also presents new challenges to its control system.In the face of such strong parameter uncertainty,security requirement is high,the cost is high,the control response lag,run interference of strong nonlinear system,want to control it to achieve strong robustness,fast response,high control precision of target is difficult,and the sliding mode variable structure control to control such a system has a certain advantage.The main research contents of this paper are as follows:Firstly,the operation mechanism of combustion type high speed wind tunnel is modeled,and the composition and function of combustion type high speed wind tunnel are introduced.The control system of high speed combustion wind tunnel is established by choosing the input of three components fuel as the control quantity and the pressure value of the wind tunnel test section as the feedback quantity.A simplified zero-dimensional model was used to build a centralized parameter model of the heating chamber and its dynamics model was established.Finite element analysis method is used to model the wind tunnel pipe by FLUENT tool(CFD analysis tool)in ANSYS software.The output of the wind tunnel heating chamber model is connected with the input of the pipe model to form a complete wind tunnel simulation system.Then a step signal is input to the simulation system to draw the step response image of the test section pressure.Aiming at the problem that the operating mechanism model can not be directly applied to the control,the identification of wind tunnel system based on Kalman filter is carried out.By using the direct identification method for the step response of wind tunnel,an identification model with large time delay can be obtained.Using Smith predictor to control the identification model,the control effect is good,but the model requires high accuracy and poor robustness.When the model perturbation occurs,the system will oscillate and diverge.Therefore,according to the robustness requirement of wind tunnel control,the sliding mode variable structure control with strong robustness is selected.The simulation results show that the control system is robust and insensitive to system parameter perturbation and disturbance.However,this control algorithm can only guarantee the asymptotic convergence of the wind tunnel system,which can not meet the requirements of fast response of the wind tunnel system,so there is still room for improvement.The finite time control is proposed for the fast response of wind tunnel system.The terminal sliding mode control after changing the sliding mode surface can be proved to be able to ensure the convergence of the system state in a finite time and has good robustness.The simulation results show that the response speed of the system is improved effectively,but the chattering problem of sliding mode control always affects the control effect of wind tunnel system.The reason of chattering in sliding mode control is analyzed,and it is considered that the chattering is caused by discontinuous control,and the chattering problem is more aggravated and even divergent when the system with time delay is encountered.Using time delay compensation method to offset the initial item chattering eliminating chattering problem,but there is need to custom to eliminate a matter of time.The chattering is transferred to the higher order term to eliminate the chattering by using the super helix control algorithm.The simulation results show that no chattering occurs after the system is adjusted and the system moves smoothly on the sliding surface.At the same time,the super spiral sliding mode control also has the advantages of finite time convergence and strong robustness,which is suitable for wind tunnel systems with inaccurate models and large time delay.