Key Technology Research On Fold Modeling And Multi-field Coupling Of Inflatable Aerodynamic Decelerator

With the rapid development of aerospace,aviation,weapon and other fields,traditional rigid re-entry spacecraft with parachute deceleration can no longer meet the future high-altitude,high-speed,and large-load deceleration requirements.The flexible Inflatable Aerodynamic Decelerator(IAD)has the characteristics of heavy load,light weight and low cost,which has become a research hotspot in the field of recovery and landing,and has broad application prospects.However,the related theory of inflatable aerodynamic decelerator is immature,and some key technologies have not been broken through,which leads to the failure of flight experiments in many countries.This paper mainly focuses on two key issues of fold modeling and multi-field coupling to conduct research,aiming to gradually build the theoretical system and analysis method of IAD,and provide the basis for its strength check and optimization design.The specific work of this paper is as follows:(1)Research on new fold modeling methodsFold modeling is the first key problem to be solved in study of inflatable deployment of flexible fabrics.The existing folding methods cannot establish a multi-dimensional folded and large compression ratio complex folding model for IAD with undeveloped surfaces.So this paper proposes two new fold modeling methods: Segmentation Mapping Folding Method(SMFM)based on geometric relation and Motion Folding Method(MFM)based on Dynamics.SMFM establishes a radial folding model of undeveloped surface with large compression rate through the " curved surfaceflattened planes-folded surface " technical solution;while MFM establishes a folding model with large compression ratio in multi-dimensional axial direction,based on the actual folding process and the principle of dynamic motion.Combined with initial stress correction technique,the above folding model can reduce stress concentration and mesh distortion during inflation process.The applicability and accuracy of SMFM and MFM in this paper are verified by fold modeling and inflation calculation of torus and sphere.Using the new fold modeling methods,this paper establishes radial folding model and rotary folding model of IAD,carries out inflation numerical calculation for these two folding models,studies the change laws of shape,pressure and volume during inflation process,and analyzes the influence of inflation speed on inflation process.Numerical results show that: folding models under the two folding methods can be expanded stably and orderly,but MFM folding model has more folding layers,larger volume compression ratio,and higher resistance during inflation expansion than SMFM,and the folds at crease are not easy to open,the volume and pressure curves in each torus show a step change.Increasing inflation speed,local stress concentration and pressure curve fluctuation of MFM folding model can be reduced.(2)Research on aerodynamic thermal protection performance based on structure heat transfer couplingDuring flight,the Thermal Protection System(TPS)of IAD will be subjected to continuous and intense aerodynamic heating,which can easily change and damage the material propertie.Therefore,it is very important to evaluate thermal protection performance of TPS.But the traditional unidirectional coupling method of aerodynamic heat and heat transfer does not consider the feedback of structure wall temperature to flow field,which will produce a large heat flux error,resulting in low accuracy of thermal protection performance evaluation.Aiming at above key issues,this paper develops bidirectional coupling method of aerodynamic heat and heat transfer,in which mapping point interpolation method ensures the temperature equality and heat flux matching on both sides of coupling surface.And the accuracy of coupling method through numerical simulation of aerodynamic heating of cylinder is verified.On basis of the above,a bidirectional coupling model of aerodynamic heat and heat transfer of IAD during flight is established,and the spatiotemporal variation law of aerodynamic heat and structure temperature during deceleration flight are studied.Numerical results show that the heat flux and temperature of flow field first increase and then decrease during the flight of IAD,and the time of temperature peak is later than that of heat flux peak.In early stage of flight,the inward conduction heat flux is greater than the outward radiation heat flux of structure surface,and structural layers continue to heat up;while in later stage of flight,due to the high temperature of structure,the outward radiation heat flux is greater than inward conduction heat flux,and structure layers dissipate heat to outside.The temperature and heat flux of each layer of TPS gradually decrease along the meridian direction,and the temperature difference of insulating layer of TPS is largest along the thickness direction.Compared with traditional unidirectional coupling method,the bidirectional coupling method in this paper dynamically reflects the dynamic changes of ambient temperature,aerodynamic heat and heat conduction of thermal protection layers,which is more in line with physical reality.(3)Research on fluid-structure coupling based on composite material modelThe amount of solid mesh modeling of thermal protection system is extremely large,and the existing researches are simplified to an isotropic single-layer shell,which will bring great error and can not reflect the multi-layer structure material difference of IAD.In order to solve above key problems,this paper proposes a large-deformation fluid-structure coupling numerical simulation method combined with composite material model.The accuracy and high efficiency of this coupling method are verified by the bending of the sandwich panel,the flow around a cylinder and the inflation of supersonic parachute.On basis of the above,this paper establishes a fluid-structure coupling model of IAD at different angles of attack,studies the dynamic change law of aerodynamic force,structural stress,and the influence of angle of attack on working performance.Results show that the deformation and oscillation of flexible structure is the main reason for periodic oscillation of aerodynamic coefficient,which reduces the drag performance of IAD.As the angle of attack increases,the shock wave,expansion wave,and wake vortex in flow field all change significantly,and the oscillation frequency of aerodynamic coefficient curve decreases and the amplitude increases.The stress of each layer of TPS oscillates up and down along the meridian direction,decreases first and then increases along the thickness direction,and the stress in the innermost layer is far greater than other layers.With the increase of angle of attack,the stress of each layer increases continuously.The structural dangerous point is located at the junction of the TPS and the centerbody,and innermost layer should be made of high strength load-bearing materials.(4)Research on fluid-structure-thermal coupling of IADWhen flying at a high speed,flexible IAD will be subjected to huge aerodynamic force and aerodynamic heat,which can easily cause material property changes and structural damage,this is a fluid-structure-thermal coupling problem.Due to the large deformation motion of the coupling surface during multi-field coupling of flexible IAD,the traditional dynamic mesh method will have the problem of negative mesh volume,while the immersion boundary method cannot accurately calculate the aerodynamic heat.In order to solve these key problems,this paper develops a new numerical simulation method of fluid-structure-thermal coupling,which combines the bidirection fluid-structure coupling method and the unidirection thermal-structure coupling method.In this fluid-structure-thermal coupling method,the immersed boundary method is used to deal with the large deformation motion of the coupling surface,which avoids the negative volume problem of the mesh,and the finite volume method is used to improve the computational accuracy of aerodynamic heat.The accuracy of the coupling method is verified by the hypersonic flow around cylinder.On basis of the above,this paper establishes a fluid-structure-thermal coupling model of IAD under extreme aerodynamic thermal load and performs numerical calculations.The surrounding flow field and aerodynamic performance,the temperature distribution of structure,structural deformation and stress distribution are studied.Results show that when the external dynamic pressure is small and internal pressure of torus is large,the deformation of flexible structure has small influence on flow field evolution process,flow field structure,and IAD drag performance.Along the meridian and thickness direction,structure temperature decreases continuously,shoulder temperature difference is large,and windward side wall temperature is far greater than leeward side.Aerodynamic heat significantly increases the stress in each layer of TPS,and changes structure stress distribution law,the location of dangerous points and dynamic deformation law of structure.The research results of this paper are of great significance to improve the fold modeling theory system of complex surface,reveal the multi-field coupling working mechanism of IAD,and optimize the design of IAD.