Numerical Study Of Maneuvering Flight Of Vehicle Coupling Aerodynamics And Control

Modern advanced aircrafts are in persuit of rapid maneuverability at high angles of attack,which could quickly change the pointing direction of the vehicle nose and obtain benificial fighting attitude.However,the aerodynamic forces/moments have strong nonlinear and unsteady characteristics as the vehicle is flying at high angles of attack or doing rapid maneuvers.There are still not unified directing criteria about how to estimate the effect of the unsteady aerodynamics in the design of the aerodynamic maneuvering layout,or how to make compensations in the desin of the flight control system.This leads to the blindness existed in the design process.The numerical simulation techniques about maneuvering flight integrating aerodynamics and flight control are developed,which could couplingly solve the unsteady flow field,the motion of the vehicle and the control of the flight together,and then could simulate the maneuvering process of the vehicle in real time.As the whole unsteady effects of the aerodynamics induced by the unsteady flow,the motion of the vehicle and the deflection of the fins on the flight control system(FCS)are considered,it is especially suitable to investigate the unsteady aerodynamics of vehicles flying at high angles of attacks or making rapid maneuvers,and to evaluate the performance of the FCS under unsteady aerodynamics.It will be of important significance to reduce the developing period and to decrease the dependence on the flight tests.In this dissertation,studies are carried out on several key techniques of this simulation method integrating aerodynamics and flight control,including: the dynamic chimera grid technique,the simulation of the 6-DOF(Degree of Freedom)coupling motion of vehicles,the rapid prediction technique of dynamic stability derivatives based on Harmonic Balance Method(HBM),and the coupling simulation technique of Computational Fluid Dynamics(CFD)and PID(Proportional Integral Differential)controller.In this way finally a software platform for numerically virtual flight is built up.A square cross section vehicle is then taken as an example to display the study of the flow mechanism and applications.The characteristics of the aerodynamics and the motion of the vehicle,the open-loop response with respect to the deflection of the fins,and the closed-loop process of manipulation are investigated in detail using the developed method.There are nine chapters in this dissertation,and the contents in each chapter are listed as below.Chapter 1 is the introduction.The background of the research is introduced firstly.Then the significant progresses of simulation technique coupling aerodynamics and flight control in recent years sre reviewed,including the computational method of the unsteady flow,the moving grid technique,and the coupling simulation of CFD and FCS.At last,the main work completed in this dissertation is briefly described.In the second chapter,the numerical methods adopted in this dissertation are presented,including the governing equations,numerical flux schemes,time-marching methods,and the boundary conditions.The transonic flow around the airfoil,the supersonic flow around the vehicle and the forced pitching motion of the airfoils are simulated to demonstrate the developed numerical method.Chapter 3 covers the developed harmonic balance method.The mechanism and realizing process of HBM are introduced in detail.Some typical test cases are simulated to study the computational efficiency and accuracy and the cost of memories,including the forced pitching of the transonic flow around the airfoil,hypersonic flow around the blunt cone and supersonic flow around the basic finer geometry.Also the adaptive area of HBM used in the prediction of dynamic stability derivatives is studied based on the test case of supersonic flow around the basic finer geometry.Chapter 4 is about the simulation method of the 6-DOF coupling motion.The coupling solution technique between CFD and RBD is introduced.To validate the developed CFD/RBD coupling solution technique,test cases of the translation of mass center,the spinning and rolling of the cylinder,and the flight trajectories of the debris shedding from the Space Shuttle are simulated.Chapter 5 is about the dynamic grid techniques.Two techniques including that of the deformation grid and the chimera grid are introduced.Test cases including typical benchmark problems of an airfoil,a two-part airfoil,and a three-part airfoil 30P-30 N are run to demonstrate the dynamic grid technique developed.The accuracy problem of interpolation where a shock is crossing the intopolating area is investigated about the hypersonic flow around the blunt cone.The dynamic chimera grid technique is also verified through the test case of forced pitching process of an airfoil.Chapter 6 to Chapter 9 are about the applications of the square cross section vehicle using the developed method.Chapter 6 is the investigation about the aerodynamic characteristics of the configuration.The pitching and rolling aerodynamics at various angles of attack and rolling angles are studied,and the aerodynamic characteristics were validated by the simulation of the free oscillation process.The influences of rapid nose-up motion and forced pitching oscillation to the characteristics of rolling are also studied.Chapter 7 is the investigation of dynamic response of the vehicle motion with respect to the deflection of the fins.The deflection of the fins is simplified to the types of step,pulse and sine functions.The performance of the dynamic response is analyzed through this open-loop simulation.The mass center and the moment of inertia is adjusted to improve the performance of the open-loop response,solving the existed problems such as the poor maneuverability and the too many times of oscillations.At last,the differences of the dynamic response between 1-DOF and 3-DOF cases are analyzed.Chapter 8 is the invetstigation about the control system of the vehicle.The design process of PID controller is introduced,including the establishment of the aerodynamic model,the modification of this model and the parameters confirmation of the PID controller.Finally,the virtual flight simulation technique coupling CFD,RBD and FCS is developed.For the control of pitching attitude,four different actions are applied to evaluate the performance of the designed PID controller.For the rapid maneuver and the flight at high angles of attack,the present method is carried out to study the lag effect of FCS induced by the unsteady effect of aerodynamics.The control and preserving of rolling attitude are also studied.Chapter 9 is the conclusion.The work accomplished in this dissertation are summerised,the diffciencies existed are pointed out and the future work are brought out.At last,the acknowledgements and references are presented.