PID控制器与CFD的耦合模拟技术研究及应用

Research and application of coupled simulation techniques of PID controller and CFD

飞行控制系统(FCS)与计算流体力学(CFD)的耦合求解是一个崭新的研究领域。传统的飞行控制系统的工程仿真方法依靠气动力模型或气动力数据库得到不同飞行姿态的气动力;而当前方法通过耦合求解Navier-Stokes方程和刚体动力学方程(RBD)以获取飞行器运动过程实时流场和非定常气动力。由于充分反映了气动力的非定常、非线性效应,因而从根本上保证了飞行控制系统仿真的精度。以方形截面导弹俯仰姿态控制为例,首先给出了系统的传递函数,并基于系统在单位阶跃舵偏操纵下的开环响应特性,提出了传递函数的修正方法,进而设计了该外形俯仰姿态控制的PID控制器。数值模拟了不同控制参数时,P控制器、PD控制器和PID控制器的控制效果。针对不同的控制指令,根据建立的控制律,数值模拟了飞行器在PID控制器作用下的实时响应过程,最终成功实现了对飞行器的俯仰姿态控制。研究发现,当飞行器作慢速机动时,工程仿真与CFD数值计算的结果吻合很好,两种方法可以互相验证;但快速机动时,两种方法给出的结果差异明显,基于CFD的耦合模拟方法由于模拟了飞行器运动和舵面偏转导致的非定常流动过程,其结果比基于静态气动力的工程方法的可靠性更高。在大攻角和快速机动等非定常效应较强时,采用CFD方法评估和验证飞行控制系统是很有必要的。

It is a novel research field to couple computational fluid dynamics（CFD）into the simulation of flight control system（FCS）.In engineering simulations of FCS,the aerodynamics of the vehicle is given by the aerodynamic models or aerodynamic databases,while in this coupled way,they are obtained by solving the Navier-Stokes equations/rigid body dynamics（RBD）equations.Thus the unsteady and nonlinear portion of the aerodynamics is adequately reserved,which guarantees the accuracy of simulation of the FCS.Taking the control of the pitching attitude of a square cross section missile as an example,the transfer functions about the vehicle motion system are first given,and modifications to transfer functions are conducted based on the open-loop response characteristics of the system to unit step fin-deflection maneuver,then the PID controller for the control of the pitching attitude of the vehicle is designed.Control effects about the P,PD and PID controller are numerically investigated with various control parameters.According to different control commands,the real-time response process of the vehicle under the PID controller is numerically simulated and the attitude control of pitching motion of the vehicle is finally reached.The investigation shows that when the maneuver action is slow,the simulation results based on CFD show good agreement with those based on the engineering simulation,while when the maneuver action is rapid,the two results have significant differences.The present method,which simulates the unsteady flow process induced by the vehicle motion and the fin-deflection,is more reliable than the engineering simulation method based on static aerodynamics.This indicates that it is of great necessity to predict and validate the FCS utilizing CFD method in the case of strong nonlinear effects including high angles of attack and rapid maneuver.