Research On The Critical Aerothermoelastic Problems For Air-breathing Hypersonic Vehicle

Hypersonic vehicle is the technological commanding height of the future aerospace field.Both the limitation of structure weight and the severe aerodynamic heating effects would reduce the structure stiffness,leading to the increasingly prominent problems related to aerothermoelasticity.Besides,aerothermoelasticity is a complex and multidisciplinary coupling problem involving aerothermodynamics,unsteady aerodynamics,structural heat transfer and structural dynamics.Therefore,aerothermoelasticity has become a focus and a difficulty point in the current researches on hypersonic.A number of aerothermoelastic problems can be induced both in the external and internal flow of the air-breathing hypersonic vehicle.The aerothermoelasticity of the wing and the rudder surface which are the main aerodynamic components in the external flow would affect the aerodynamic characteristics and structural safety of the vehicle.The aerothermoelasticity of the inlet and the combustor which are important parts of the scramjet will have effects on the performance of the propulsion system.In addition,the aerodynamic nonlinearity and the aerothermodynamic nonlinearity caused by the complex wave structure in the internal flow as well as the structural dynamic nonlinear of the panel make the internal aerothermoelasticity extremely complicated.However,in the present studies,problems of the first kind mainly apply engineering simplification methods,which cannot analyze the physical processes and laws of the aerothermoelasticity more accurately and deeply.At the same time,there have been rare researches on the problems of the second kind.Therefore,relevant researches on the aerothermoelasticity both in the external and internal flow of hypersonic vehicle were conducted in this paper.The main works are as follow:(1)A static aerothermoelastic framework based on CFD/CTD/CSD was established,and the physical processes and effects of the static aerothermoelasticity on the wing were analyzed in detail based on the framework.(1)Aerodynamic heating process and the effects of the aerodynamic heating on the elastic deformation characteristics and the aerodynamic characteristics were studied.It was found that the aerodynamic heating changes the distribution of deformed torsion angle along span.Aerodynamic heating makes the torsion angle extend from monotonic increase to first increase and then decrease.The mechanism is that more intense aerodynamic heating on the leading edge leads to a larger deformation amplitude.(2)The aerothermoelastic deformation makes the lift,the drag,the lift drag ratio and the torque of the wing decrease,especially the change of the torque,which is because the aerothermoelastic deformation reduces the effective angle of attack.Therefore,this study helps deepen the understanding of static aerothermodynamic of the wing.(2)An efficient framework of dynamic aerothermoelasticity was established.Aerodynamic heating was predicted based on twice steady flow solution using CFD,and the efficiency of aerodynamic heat prediction improves greatly in the condition of certain computational accuracy.The aerodynamic heating of the rudder shaft and its vicinity increases the temperature and thermal stress of the rudder shaft,reduces the structure natural frequency and frequency spacing,and eventually causes the flutter boundary decrease further.(3)A parametric model of temperature distribution was put forward.What's more,a framework of uncertainty and global sensitivity analysis for dynamic aerothermoelasticity based on the Monte Carlo Simulation(MCS)and Spare Grid Numerical Integration(SGNI)was established.Based on this framework,the effects of uncertainties of structure temperature distribution on the structure stiffness and the flutter characteristics of rudder were studied.The results show that the SGNI method greatly improves the efficiency of uncertainty analysis while the accuracy can be ensured.(4)The effects of the static and dynamic aerothermoelasticity of the inlet on the structure deformation,the structure dynamic responses,separation vortex structure,the inlet performance and the mechanism were deeply studied.(1)The effects of aerodynamic heating and coupling model(one-way and two-way)on the analysis results were considered.The effects of aerodynamic heating on the analysis results are larger,while the differences caused by coupling model are less significant.(2)Aerodynamic heating makes the amplitude of structural vibration increases obviously.In addition,a complex "Beat" effect occurs in the structure dynamic response.(3)The largest deformation and vibration amplitude appear on the leading edge which increases the intensity of the shock wave and leads to the scale increase of the boundary layer separation vortex,the outlet flow field is changed as well.The structure deformation and vibration increase the time averaged flow coefficient and the pressure rise ratio,and reduce the time averaged total pressure recovery coefficient.The structural vibration causes the fluctuation of the performance parameter.And the fluctuation amplitude of the pressure rise ratio is relatively large.The researches can help understand the aerothermoelasticity of the complex wave structure in the inlet more deeply.(5)The effects and mechanism of the plate vibration on the flow field structure,the mixing characteristics and the combustion performance of the supersonic transverse injection in the scramjet combustor were studied.(1)The effects of vibration frequency and amplitude on the performance parameters were studied.The vibration frequency has little influence on the performance parameters,while the vibration amplitude has great influence on that.It was also found that large vibration amplitude leads to combustion instability,making the combustion performance parameters fluctuate greatly.(2)The effects and mechanism of the plate deformation and vibration on the mixing characteristics and combustion characteristics were studied.The plate vibration and deformation increase the intensity of shock wave,the number of shock waves and the intersection number between the shock wave and the injection mixing layer,and improves the momentum flux ratio and jet penetration depth,which lead to that the total pressure loss coefficient increases while improving the mixing efficiency and combustion efficiency.(3)The combustion instability characteristics under large amplitude vibration were analyzed based on flow field data and DMD method.The first six-order unstable DMD mode was analyzed.The flame structure of unstable mode mainly appeared near the plate vibration area,and mainly present high-frequency mode.The researches above could help understand the effects of the plate vibration on the injection combustion performance and stability more deeply.