Mach Number Of Wind Tunnel Modeling And Identification

Wind tunnel is a device in which aerodynamic experiments of early aircraft design are done. The stability and control precision of wind tunnel’s Mach play an important role in the experimental results. So highly accurate Mach model is of important significance in the flow control of wind tunnel system. This paper takes SJ-30 wind tunnel as the object.First the total pressure and the static pressure are studied as two factors of wind tunnel on account of wind tunnel’s aerodynamic structure, aerodynamic air circulation model and the characteristics of flow experiments. Then the Mach model is built by the total pressure and the static pressure modeling. Because of the wind tunnel’s nonlinear, time-varying, strong coupling and other characteristics and the NARMAX model’s high precision, simple structure, fast convergence and other characteristics. The total pressure and static pressure models are built by Non-linear Auto-Regressive Moving Average model with exogenous inputs.The order of variable in NARMAX model is meaningful for modeling precision. In order to obtain the order of the model variables, the embedding dimension and delay time of phase space reconstruction are introduced. First the variables’ sampling intervals are obtained with mutual information algorithm, then the orders of variables are got using false nearest neighbors algorithm. Finally the models’parameters are obtained through simulation analysis.The total pressure and static pressure NARMAX models are identified by the NNSYSID tools of BP neural network with experimental data of three conditions. The results prove that the method that the models’ parameters are obtained with mutual information algorithm and false nearest neighbors algorithm is reasonable. According to the characteristics of start-up stage, steady pressure stage and steady Mach stage,three models of wind tunnel are built and identified. The results illustrate it is important to improve model precision.It is applicable to build Mach of wind tunnel model with NARMAX model. The Mach model plays an important role in highly accurate control.