Supersonic, Hypersonic Nonlinear Aeroelastic Research

Using the engineering methods of supersonic and hypersonic flow or local piston theory developed in this paper to compute unsteady aerodynamic loads, and coupling structural equations, the supersonic or hypersonic aeroelasticity with a typical servo system under thermal environment is simulated in time-domain.Analyzing existing engineering methods, we combine them in such a way to make computing aerodynamic characteristics possible for arbitrarily shaped body. Comparing with CFD results and experimental dates, the combined engineer method has a practical application and we extend it to solve the unsteady pressure distribution of supersonic or hypersonic aircraft. Employing Euler based steady solution and piston theory, a new method (we call it local piston theory in this paper) to solve supersonic or hypersonic unsteady loads has been developed. The results are compared with unsteady numerical method and piston theory. Local piston theory can be applied to projects better than piston theory for the high precision, and the wide application range. Compared with the unsteady Euler codes, it is an attractive way for its time saving in computing supersonic or hypersonic flutter.Using above methods to solve unsteady pressure distribution, coupling structure equations, the supersonic or hypersonic aeroelasticity is simulated in time-domain. The computed flutter speeds are within 10% of experimentally determined ones. Several non-linear phenomena are also analyzed.By using uncoupled thermal-structure analyzing method, with the consideration the additional stiffness caused by thermal stress, the finite element model for thermal-vibration analysis is obtained and two typical hypersonic wing structures are computed. Using local piston theory based on CFD to solve hypersonic unsteady aerodynamic loads, the hypersonic aerothermoelasticity is simulated in time domain. The different influences of temperature to two aeroelastic systems are analyzed.The transfer function of the servo system in Laplace-domain is transformed to time-domain to produce the servo state equations. By solving aerodynamic equations, structure state equations and servo state equations in every time step, the aeroservoelastic problem can be simulated in time domain. By numerical simulation, the servo system in this paper greatly reduces the aeroelastic stability. The structural flitter added to the system can reduce the coupling effect of servo system and structure mode and increase the flutter velocity. Using control surface, control law is designed based on the energy viewpoint of flutter. A linear saturated law is used to restrain flutter. The critical velocity can be improved more than 30%. The effects of the parameters of the flutter restrain system are analyzed.