Research On Modification And Adaptability Of Transition Model Based On Local Variables In Hypersonic Flow

Boundary layer transition is an important factor that affects the precise prediction of the lift-to-drag ratio of a hypersonic vehicle and the aerodynamic thermal environment,and is directly related to the reliable design of the payload and thermal protection system of the hypersonic vehicle.The method of solving the Reynolds mean NS equation based on the transition model theory is currently an important means to carry out boundary layer transition prediction.However,since most transition models are developed from low-speed flow,and there are usually a large number of empirical formulas and model constants in the model,they are also based on the research of low-speed boundary layer transition theory and experimental data.Therefore,when the transition mode method is used to carry out the research on the transition of the hypersonic boundary layer,it is necessary to carry out the research on the correction method of the transition mode,such as compressibility,and to detect the applicability of the transition mode to the prediction of the transition of the hypersonic boundary layer.In this paper,based on a detailed analysis of the four common types of typical transition pattern construction methods,we choose theγ-Re_θtransition model based entirely on local flow field variables.Using the hybrid scheme of Godunov and Steger-Warming that can simultaneously meet the requirements of hypersonic shock wave capture and high resolution of the boundary layer,the transition prediction method of hypersonic boundary layer is established.In this paper,the originalγ-Re_θmodel is studied for compressible correction,temperature correction,cross-flow correction and head bluntness correction,and aγ-Re_θ-MT modified transition model suitable for hypersonic boundary layer transition prediction is formed.In this paper,the γ-Re_θ-MT modified model is used to study the effect of incoming turbulent pulsation intensity,Mach number,Reynolds number,angle of attack,head bluntness,and temperature on the transition of hypersonic boundary layer.In this study,it was found that it is not sufficient and clear to study the transition of hypersonic boundary layer using the combined temperature-temperature ratio parameter.Therefore,by decomposing the wall temperature ratio,the effects of the incoming temperature and the wall temperature on the transition were studied respectively.The results show that when other parameters are kept unique,the transition will be suppressed by increasing total inflow temperature or the decreasing wall temperature.In this paper,by combining theγ-Re_θ-MT correction model and the thermochemical non-equilibrium model,the transition prediction method under thermochemical non-equilibrium conditions is established,and the calculation and analysis of the Reentry-F profile flight test are carried out to explore the effect of the high-temperature gas effect on the boundary layer transition.This article is divided into seven chapters.In the introduction,it briefly introduces the current research significance of hypersonic boundary layer transition,transition type,main prediction methods and main problems of different prediction methods,and then introduces the work carried out in this paper.Chapter 2 introduces the working mechanism of the originalγ-Re_θtransition model and the numerical method adopted in this paper.This paper first introduces the mechanism and working mode of the transition prediction ability of theγ-Re_θtransition model,and analyzes the problems and reasons if the transition model is extended to the hypersonic boundary layer transition prediction.Then,the four equation transition model equations and the numerical methods used in this paper are given in detail.The advantages and disadvantages of the transition prediction results in 8different numerical schemes are carefully compared and analyzed,which shows the necessity of using low-dissipation numerical scheme for hypersonic transition prediction with transition model.In this chapter,the grid-independent research is carried out in conjunction with the boundary layer transition prediction problem of the flat shape.The results show that the transition prediction method established in this paper is less sensitive to the flow grid and the normal grid.Chapter 3 introduces the hypersonic correction method of the originalγ-Re_θmodel.The research in this paper found that when the originalγ-Re_θmodel was used to predict the transition of hypersonic boundary layer transition,the length of the transition region obtained was too long.Therefore,in this paper,combined with the characteristics of hypersonic flow field compression and strong thermal diffusivity in the boundary layer,the compressive correction and temperature correction methods of theγ-Re_θtransition model were studied,and a correction method based on turbulent Mach number and reference temperature was established.Aγ-Re_θ-MT modified transition model suitable for hypersonic flow is formed.The revised model can effectively improve the prediction accuracy of the transition position and the length of transition zone,and all the correction methods are completely dependent on local flow field variables,without changing the advantage of the model based on local variables.This paper also carried out cross-flow correction research on theγ-Re_θ-MT correction model by introducing the helicity cross-flow correction method.The transition prediction results of a hypersonic lifting body standard model show that when there is a strong lateral flow,a cross-flow correction must be carried out to obtain a reasonable transition front.Chapter 4 focuses on the research on the adaptability of the transition predition method is carried out in view of the relatively sufficient typical hypersonic boundary layer transition influencing factors.In this chapter,the transition prediction method based on theγ-Re_θ-MT modified model is used to study the inflow turbulent pulsation intensity,Mach number,Reynolds number,head bluntness,angle of attack,and the effects of these five factors on the hypersonic boundary layer transition are analyzed.In this paper,by analyzing the internal flow field structure of the boundary layer and the characteristics of the profile parameters of typical stations,the influence rules and mechanism of these factors on the transition are studied.The results show that the method established in this paper can correctly reflect the law of increasing the turbulent pulsation intensity of incoming flow,the Reynolds number of incoming flow to promote the transition,and increasing the Mach number of incoming flow to delay the transition.In this paper,based on the modifiedγ-Re_θ-MT model,further research on the method of head bluntness correction is carried out.The results show that the head bluntness correction method established in this paper is capable of predicting the phenomenon of"turning and reversing"of the hypersonic boundary layer caused by head bluntness,and the predicted position of the turning position is consistent with the experimental results.Based on the ballistic target test results of the Super Speed Institute of China Aerodynamics Research and Development Center,this paper also conducted a preliminary study on the impact of the coupling factors of angle of attack and head bluntness on the transition.The results show that the transition law of the hypersonic boundary layer under the coupling effect of the angle of attack calculated and the bluntness of the head is consistent with the experimental results.Chapter 5 investigates the influence of incoming temperature,wall temperature and wall temperature ratio on the transition of hypersonic boundary layer.In this paper,the main influencing factors of the transition are derived from the dimensionless NS equation,and it is found that the inflow temperature T∞and the wall temperature Tw will affect the transition solution in two different paths.Taking the 7°cone shape as an example,firstly,by changing the Mach number,Reynolds number,and turbulent pulsation intensity of the incoming flow,the total temperature of the incoming flow was changed,and the influence law and mechanism of the incoming temperature on the transition were studied.Then,under the condition that the flow field parameters and turbulent pulsation are exactly the same,by changing the wall temperature of the model,the effect of the wall temperature on the transition is discussed.Finally,by fixing the Mach number,Reynolds number,and turbulent pulsation intensity,and keeping the wall temperature ratio always equal to 1,the transitions under different flow conditions were studied.The results show that the wall temperature is fixed,and the increase of the total temperature of the incoming flow inhibits the occurrence of transitions;fixed conditions of the incoming flow,lowering the wall temperature will also inhibit the occurrence of transitions.Under the condition that the wall temperature ratio is always 1,the velocity and temperature of the outer layer and the bottom layer of the boundary layer under different flow conditions have"antagonism".As a result,the onset position of the transition is different due to the temperature of the inflow.This chapter also uses the three-dimensional boundary layer linear stability analysis method to analyze the growth and development of unstable waves in the boundary layer under different conditions.The results show that the stability analysis results are consistent with the conclusion of the transition mode method.Research on the effect of temperature on the transition of the hypersonic boundary layer shows that the transition position measured in the conventional hypersonic wind tunnel with low total temperature is earlier than the actual flight conditions with high total temperature.Therefore,when conducting a hypersonic boundary layer transition wind tunnel experiment,the Mach number,Reynolds number,and incoming turbulence pulsation intensity cannot be used as the only transition simulation similar parameters.The difference between the ground wind tunnel test and the flight conditions must be considered,and the wall temperature ratio cannot be used as an overall factor to measure the temperature difference.It is needed to reproduce the incoming flow temperature as much as possible.In chapter 6,a study on the effect of thermochemical non-equilibrium effects on transition is carried out for the high-temperature gas phenomenon that often accompanies the high Mach reentry process of hypersonic vehicles.In this paper,theγ-Re_θ-MT modified transition model is combined with the thermochemical non-equilibrium calculation model to establish a transition prediction method that can consider the 5-component air chemical reaction model and the dual-temperature thermodynamic non-equilibrium model.Then this method is used to carry out transition calculations for the Reentry-F profile that has undergone free flight experiments abroad,and the differences in flow field structure,boundary layer profile parameters and boundary layer transition positions caused by thermochemical non-equilibrium effects are analyzed.Finally,by changing the head radius of the Reentry-F aircraft,the paper analyzes the effect of head bluntness on the transition calculation results under thermochemical non-equilibrium conditions.The results show that after considering the thermochemical non-equilibrium effect,the transition position shifts significantly relative to the calorimetric complete gas condition,and the increase of the head bluntness within a certain range will delay the transition.Chapter 7 is the conclusion and acknowledgement.A revised study on the originalγ-Re_θmodel was carried out in this article,aγ-Re_θ-MT modified model suitable for the prediction of hypersonic boundary layer transition has been formed.And the transition prediction method were established under the conditions of hypersonic calorimetric complete gas and high temperature thermochemical non-equilibrium gas.This method can accurately reflect the influence of typical factors on the transition of hypersonic boundary layer transition,with good robustness and no artificial parameters.It has the engineering potential to be widely applied to the rapid prediction of the transition of a three-dimensional complex shape aircraft under hypersonic conditions.