Thermal Coupling Calculation Of Ablation And Structure Of Supersonic Vehicle And Analysis Of Aero-servoelasticity

The research of this thesis is focused on the heat transfer analysis of ablative thermal protection coupled with structure of the supersonic aircraft with the aerodynamic heating and the modeling and analysis of the aero-servo-elasticity. The vibration of the structure induces the unsteady aerodynamic force, and the aerodynamic force changes the structure deformation. Under the protection of the ablative system, the structure deformation of the aircraft caused by aerodynamic heating is much smaller than that caused by structure vibration, so it has little influence on the unsteady aerodynamic force. When the amplitude of structure vibration is small, the influence of it on aero-heating can be neglected, but the temperature rising caused by aerodynamics changes the natural frequencies and modal shapes of structure. In the analysis of dynamic aero-elasticity problem, the governing equations are always established in the modal coordinates, so the influence of the aero-heating on the natural frequencies and modal shapes cannot be ignored.The changing of the transient temperature field of the structure with time results that the structural dynamic characteristics also changes with time, which make the structure a time-varying system. It is known that the cycle of the structural vibration is much shorter than the characteristic time of the temperature changing of the structure, so the temperature field can be solidified when the time period of the structural dynamic analysis is short. The structure can be regarded as a time-invariant system approximatively, and the modal analysis with aero-heating can be carried out with the average temperature in that time period. Therefore, the multi-physics coupling dynamic problem considering unsteady aerodynamic force, aerodynamic heating&thermal protection, aircraft structure and servo control system can be divided into two individual dynamic problems:1) thermal protection-structure coupled heat transfer analysis; 2) unsteady aerodynamic force-servo-aircraft structure coupled dynamic analysis. Two problems are connected by modal analysis with aero-heating.The main work includes these following sections. 1).The thesis presents a method which combines the ablative thermal protection program with commercial FEM program. It provides an approach that can handle heat transfer and temperature field analysis of complex aircraft with ablative thermal protection. The method has been used in some engineering applications. First, the finite difference schemes of the moving boundary heat transfer problem of ablative material are deduced, and the finite difference program is validated by a simple heat transfer problem. Taking a supersonic missile as the research object, the ablative layers are installed on the surface elements of the structure where need, computer programs have been designed to exchange the data between two programs. A alternate algorithm is used to ensure that interface temperature and heat flux can satisfy the thermal equilibrium condition. After the coupled analysis of ablative protection layer and structure, the temperature rising of the structure and consumption of the ablative material are gotten. The changing of structural natural frequencies are analyzed resulting from the temperature rising.2).An unsteady aerodynamic force expression is presented and used in the aero-servo-elasticity analysis of a supersonic aircraft. Using equivalent transformation to transform some general aerodynamic models into a uniform mathematical model. By introducing some instrumental variables, this kind of mathematical model can be converted into second order differential equations as the addition items of the mass, damping, and stiffness in structural dynamic equations. Through this transformation, the aero-servo-elasticity problem can be studied by the structural dynamic methods. Taking a high-aspect ratio wing as the research object, the aerodynamic force is calculated by Theodorsen model, and the critical velocity of flutter is obtained and the equivalent transformation of the aerodynamic force is validated. Taking a supersonic aircraft with servo control system as the research object, aeordynamic force are computed by local piston theory. Through the transformation of the transfer function, the control force induced by the deflection of the control surface is converted into that uniform expression. The new coupled model of aero-servo-elasticity is obtained and stability analysis is studied by the complex eigenvalues of the system. The servo-flutter boundaries of this supersonic aircraft with different Mach numbers and different angles of attack are calculated.