Research On The Optimization Of Hypersonic Biplane Airfoil And The Aerothermoelasticity Characteristics Of Hypersonic Biplane Wings

Hypersonic aircraft is of great significance in both military and civil fields.While a series of technical problems remain unsolved during the development of hypersonic aircraft,two essential ones among which being aerodynamic problem and aerothermoelasticity problem.At present,hypersonic flight can be achieved by applying many techniques to hypersonic winged flight vehicle,such as large swept wing,low-aspect-ratio airfoil,thin wing and heat-resistant materials.And aerodynamic drag and aerothermoelasticity problem can be dealt with to some extent.Nevertheless,these techniques have never taken into account the impact of the multilayer configuration of the wing on the aerothermoelasticity characteristics.To solve the problems mentioned above,this paper puts forward a hypersonic biplane wing shape and studies the optimization of the hypersonic biplane airfoil.On this basis,three different hypersonic biplane wings are constructed by applying the shape of the improved Busemann biplane airfoil,the asymmetric biplane airfoil and the morphing biplane airfoil followed by a comparison of aerothermoelasticity problems among these three wings are carried out,which provides a new method to study the problem in the aerodynamic and the aerothermoelasticity of hypersonic vehicle.The main contents of this paper are as follows:Study on the lift-drag ratio characteristics of Busemann biplane.Firstly,the effect of increasing lift on Busemann biplane are investigated.It is deduced that the Busemann biplane has higher lift-drag ratio than the diamond monoplane based on the theoretical calculation model of the aerodynamic characteristics of hypersonic Busemann biplane in hypersonic flight are derived and the lift-drag ratio characteristics of the Busemann biplane are analyzed.Secondly the drag-reducing effect are taken into account.A subsequent analysis on the shock-expansion wave interference effect of the Busemann biplane further indicates that the Busemann biplane can enhance aerodynamic characteristics by reducing the drag.An asymmetric biplane airfoil is obtained by modelling of the optimization of aerodynamic characteristics on hypersonic biplane airfoil.In accordance with the drawbacks of large computational cost of CFD during the optimization of Busemann biplane airfoil,an optimization model that enables rapid calculation,optimization and evaluation of the aerodynamic characteristics of hypersonic biplane airfoil is established and an optimized asymmetric airfoil is proposed.At the same time,a surrogate model based on CFD calculation results is established with its accuracy of the calculation being verified that applied to the validation in the results of optimization model.The result of optimization is compared to the asymmetric biplane airfoil optimized by the theoretical model and the airfoils from both are basically identical with the shape,which indicates the relatively high computational accuracy of theoretical optimization model.A subsequent investigation of aerodynamic characteristics of the asymmetric biplane is carried out and the results indicate that the asymmetric biplane cannot maintain high aerodynamic performance under all working conditions.Furthermore,in order to improve the aerodynamic characteristics of hypersonic biplane and overcome the defects of the asymmetric biplane airfoil,a hypersonic morphing biplane is proposed,and the aerodynamic performance under different working conditions are investigated.And according to the difficulty of selecting the deflection angle of rudder on morphing biplane under given angle of attack and Mach number,this paper designs an optimization algorithm that combines the advantages of dichotomy algorithm,genetic algorithm and Gauss-Newton algorithm.The algorithm has the characteristics of higher precision and more rapid computation,which enables quick selection of the deflection angle of the rudder on the morphing biplane under different working conditions.The calculation results show that the optimization algorithm has high computing accuracy and can meet the requirements of optimization of the hypersonic morphing biplane under different working conditions,and the optimizated hypersonic morphing biplane has better aerodynamic performance.For enhancing its aerodynamic performance under considering viscidity,the conventional biplane airfoils are improved.Since the wetted area of the biplane is almost twice as large as that of the monoplane,the biplane generates larger frictional drag in the presence of viscosity,which results in their lift-drag ratio characteristics being no more favorable than those of a monoplane.And this implies that conventional biplane airfoil are not suitable for hypersonic flight.In response to this problem,the idea of shifting the incident points of oblique shock wave from the traditional throat position to the trailing edge of the biplane is proposed,meanwhile,by increasing the spacing of the biplane,the lift coefficient under considering the viscidity is improved.The results show that this change can evidently increase the lift-drag ratio of the biplane when considering the viscosity,that also has a higher value on the comparison of the lift-drag ratio characteristics of the monoplane.Since the resesrch on the static characteristics of aerothermoelasticity of hypersonic winged vehicles have not taken into account the influence of the multilayer configuration of the wings on its static aerothermoelasticity,this paper proposes the idea of solving the static aerothermoelasticity problem of hypersonic wing with biplane configuration.After studying how the sweep angle and taper ratio of wing affect the aerodynamic characteristics and the structure mode of the hypersonic biplane wing,a configuration of biplane wing for hypersonic flight is put forward,and three hypersonic biplane wings are established,the influence law of the static aerothermoelasticity of hypersonic wing by which is investigated.The study proves that the biplane wing has better static aerothermoelasticity characteristics compared to the diamond monoplane,and the aerodynamic heating effect has less impact on its aerodynamic characteristics.Due to the influence of the multi-layer configuration of the wing on its dynamic characteristics of aerothermoelasticity,the idea of solving the dynamic aerothermoelasticity problem of hypersonic wing by applying biplane configuration is presented.Based on this idea,the effect law of the critical flutter velocity of wing by the hypersonic biplane configuration is investigated.It shows that compared to the diamond monoplane,the wings of the Busemann biplane and the asymmetric biplane have better dynamic aerothermoelasticity characteristics,and critical flutter velocities are higher under the same environmental conditions.In contrast,the critical flutter velocities of the morphing biplane is sufficiently large for hypersonic flight albeit they are lower than those of the diamond monoplane under the influence of the rudder stiffness.