Studies On Aerodynamic—Structural—Thermal Modeling And Reduced Order Modeling Of Hypersonic Vehicles

Hypersonic vehicle is an important direction in future and current development of flight vehicles. The aerodynamic-thermal-structural coupled problem is one of the key technologies for hypersonic vehicles. Accurate and efficient computation of the aerothermodynamics is one of the primary challenges for hypersonic aerothermoelastic analysis. Engineering level approximations for the aerodynamic heating and aerodynamics based on relatively simple configurations and flow fields are not adequate for aerothermoelastic analysis in hypersonic flows due to these low accuracy. Computational fluid dynamics(CFD) analysis have advantages in simulation of nonlinear problems in hypersonic flows. However, low computational efficiency and large data sets in the CFD analysis restrict wide-range application in engineering field. Therefore, it is necessary to construct efficient reduced order models(ROM) for aerodynamics and aerodynamic heating, which capture dominant physical characteristics of the original system with comparable accuracy to CFD solver. What’s more, these ROMs for aerodynamics and aerodynamic heating can be incorporated into aerodynamic-thermal-structural coupled problem.Combining the researches of aerodynamic-thermal-structural coupled problem and the application background of engineering, new techniques of reduced order modeling for aerodynamics and aerodynamic heating are studied, which are intended for aerodynamic-thermal-structural coupled systems for hypersonic vehicle in this thesis.Furthermore, the computation for thermal boundary of hypersonic vehicle is discussed. The work in this thesis is as follows:(1) Flutter boundaries are obtained using classical hypersonic unsteady aerodynamic theories for a double-wedge typical section. These theories are evaluated by comparing the flutter boundaries with those predicted using computational fluid dynamics solutions.Based on the reference enthalpy method and the empirical formula, the aerodynamic heating flux of hypersonic flight vehicles was studied using the strip theory. A solution flow chart of the aerodynamic heating of airfoils of hypersonic flight vehicles was proposed,which has enough accuracy and can consider angle of attach and airfoils.(2) Utilizing sampling point idea, the physical space of hypersonic aerodynamics andaerodynamic heating are translated in to the vector space using proper orthogonal decomposition(POD). The relation between the physical space and the POD vector space are managed by the surrogate models. An approach using POD in combination with surrogate models was presented in this thesis. Test results for the three-dimensional aerothermodynamic over a hypersonic surface indicated that the ROMs for hypersonic aerothermodynamics have good precision and efficiency.(3) Aiming at improving the accuracy of ROMs for hypersonic aerodynamics and aerodynmaic heating, an enhanced algorithm of fast maximin Latin hypercube design(ESLE) based on proposed space reducing criterion and forgetful ratio is presented, which proves to be helpful to improve the precisions of ROMs using the same sampling points.Aiming at improving the efficiency of constructing ROMs for hypersonic aerodynamics and aerodynamic heating, an adding points strategy based on fuzzy clustering(APSFC) in order to improve the efficiency of the ROM framework utilized method of snapshots for hypersonic aerothermodynamics was proposed. The proposed strategy was successfully applied to ROMs for both the numerical examples and aerothermodynamics with a representative hypersonic control surface. Test results indicated that the proposed APSFC algorithm can obviously improve the efficiency of ROMs.(4) For hypersonic aerodynamics-thermal-structure coupled analysis system, an integrated analysis system is developed based on aerodynamic heating computation,transient heat transfer analysis, thermal mode analysis and thermal flutter analysis.Aerodynamic heating reduced order model was investigated in aerodynamics-thermal-structure analysis system successfully. The results showed that,comparing with approximated engineering method, gas viscidity, and real gas effects and complicated figuration will lead more severe flutter boundary. The typical example shows flutter velocity will decline more 10% with consideration of these effects, and gas viscidity,real gas effects and complicated figuration play an important role in hypersonic aerodynamics-thermal-structure coupled analysis.(5) The unsteady process coupled with aerodynamic heating, radiant heat and transfer heat is computed using a quasi-static analysis, and develop a coupled analysis method which can be applied to predict the hypersonic thermal environment boundary. This methodcan take practical flight path into consideration and realize the prediction of hypersonic thermal environment boundary with heat transfer in all flight path. The results show, the heat flux transferred into inner structure has weak influence on thermal environment on leading edge, but great influence on other area. So, the great importance should be attached to heat flux transferred into inner structure when predicting hypersonic aerodynamic heating boundary.