Numerical Investigation Of Aerodynamics And Flight Dynamics Coupling For Flight Vehicle With High Maneuverability

Strong, nonlinear aerodynamic coupling between unsteady flow and motion always occurs during severe mane uvers with high angle of attack, for the modern, advanced flight vehicles, which may result in uncommanded motions and losing control of flight. The quasi-steady aerodynamic database and model established by traditional method of wind tunnel test and CFD are only suitable for flight conditions with small angles of attack and attached flow, and cannot accurately predict the variation of the unsteady load and incidence, so times of flight tests should be conducted on the back phase of design, forming a “fly & fix” mode, which can be slow, expensive and dangerous. In recent years, The techniques of wind tunnel based virtual flight test(VFT) and integrated numerical simulation by flow/motion coupling have been developed to realistically simulate the process of real flight, verify the integrated system of aerodynamic, flight dynamics and flight control, and bridge the gap between wind tunnel test and flight test. By means of VFT and integrated numerical simulation by flow/motion coupling, a more comprehensive eva luation of aerodynamics configuration, structural strength and flight control system is hopeful to be done, making less times of flight tests, shorter design processes, lower costs and higher safety factors. In the thesis, the integrated numerical simulation technique by flow/motion coupling is introduced at first, and then the coupling motions between aerodynamics and flight dynamics for classic flight vehicles with high maneuverability are simulated. From the results, we find the roll coupling motion during the pitch maneuver of the missile, and the motion can be controlled by the decoupled control method based on roll-priority-control, keeping the attitude stable. The numerical results show good agreements with the experimental ones, indicating the method employed in this thesis can be used for the study of aerodynamics/flight dynamics/flight control coupling.The thesis has six chapters:In the first chapter, the research background is introduced, and then the progress of studies of wind tunnel based virtual flight test and integrated numerical simulation by flow/motion coupling is briefly reviewed. An introduction of main research contents is following.In the second chapter, the numerical methods employed are introduced, including the computing method for unsteady flow and flight dynamics, and the coupling method between them. The moving grid technique is also presented. The integrated, parallel numerical computing platform of aerodynamics/flight dynamics is established by combining all modules.In the third chapter, a series of standard cases are used to validate the numerical method. The viscous(both laminar and turbulent) flow over a flat plat, the viscous flow over the RAE2822 airfoil, and viscous flow over the classic missile with strakes within a large range of angles of attack are computed, validating the steady calculation ability and the moving grid technique. Then the small oscillation of the NACA0012 airfoil and deep stall of the NACA0015 airfoil are simulated, in order to validate the unsteady calculation ability and the DDES method. At last, the pitch- and roll-damping stability derivatives of the Basic Finner standard missile model are predicted, indicating the engineering practical value of the method in the field of the unsteady aerodynamic problem.In the fourth chapter, the virtual flight testing technique based on 2.4m transonic wind tunnel is first introduced, and then calculations of cases of the typical missile with strakes are performed, including the one-degree-of- freedom pitching motions with open- and closed- loop control, and the three-degree-of- freedom motions in pitching, yawing and rolling with both traditional longitudinal control and decoupled control. We can see that the numerical results agree well with the experiment and simulation results; the destabilization and oscillation in roll may occur during the pitching maneuver, leading to the longitudinal and lateral coupled motion, and making the missile lose control; the multi-channel decoupled control method based on the roll-priority-control can suppress the instability and keep the attitude stable.In the fifth chapter, the application of DES type methods in the integrated numerical simulation by flow/motion coupling is preliminarily explored. We calculate the wing-rock phenomenon of a typical wing-body configuration, using the DDES method based on S-A turbulent model. We can find that, using the DDES method can more easily acquire the wind-rock motion close to the experimental result, rather than using the traditional URANS method, which show a good application prospect for the DES type methods.In the last chapter, we review and summarize the main points of the thesis in general, and indicate the shortage of the study. At last, some considerations for the future direction are presented.