Research Of Fluid-solid Coupling Heat Transfer Characteristics For Composite Structure Nozzle

As the energy conversion device for rocket engines,the nozzle needs to withstand the scouring of high-temperature gas during the working process,the working environment is very harsh.The longer the nozzle is working,the higher the risk of rupture and burn through,which leads to engine failure or even explosion.The composite structure nozzle is widely used in the aerospace field due to its anti-ablation performance and light weight.The ablation process is a complex physical and chemical change,involving the cross-fusion of mutiple disciplines.In this paper,the heat transfer and ablation of the composite structure nozzle are studied by the method of experiment and numerical simulation.The main research contents are as follows:(1)A conjugate heat transfer program is developed to address the volume ablation and surface ablation phenomena of the anti-ablation layer of the nozzle.The finite volume method is used to solve the Navier-Stokes equations for the flow field,and heat conduction equation for the solid field.For the numerical method for the flow field,k-ω SST turbulent model were used,the third-order monotone upstream centered scheme for conservation laws(MUSCL)is adopted for convection term,the inviscis term was calculated by AUSMPW+ schemes,the central difference scheme is utilized for the viscous term,and jacobian transformation is used to compute the viscous flux.The coupling heat transfer function is realized by ensuring that the heat flux density equal and the temperature consecutive.On the basis of the above simulation methods,a thermodynamic physical property model based on pyrolysis kinetics is established to describe the volume ablation of phenolic / phenolic and the simplified chemical reaction model is used to calculate the thermal chemical ablation of the nozzle.The spring analogy is used to solve the grid generated by the nozzle inner-profile regression,a 2D local Lagrange interpolation method is used to reconstruct the solid domain after ablation.Changes in gas composition and flow parameters caused by pyrolysis and ablation are achieved by adding source terms to the governing equations.The reliability of each function of the simulation program is verified using classic examples.(2)The laser ablation device was used to study the thermochemical ablation characteristics of C/C composite materials.Scanning electron microscopy was used to study the micromorphological changes after ablation.A solid rocket motor was designed ignition experiments was carried out.The surface temperature was obtained by thermocouples,and the thickness distribution of the pyrolysis layer was obtained in the experiment,which verify the reliability of the simulation program.(3)The convective heat transfer law between the nozzle and the gas is studied through numerical simulation.Based on the temperature distribution in the solid region of the nozzle,the time and space distribution of the thermal properties of the anti-ablation layer of the nozzle,as well as the thickness changes of the pyrolysis layer and the charing layer during the engine operation is obtained.The surface ablation rate is calculated in real time by the wall temperature and the partial pressure of the reactants,the spatial and temporal distribution of the ablation amount is obtained by solving the time integration.The simulation results show that thermochemical ablation absorbs a large amount of heat,resulting in a decrease in the temperature of the inner profile,and different ablation rate distributions cause different endothermic heat.Due to the large difference of thermophysical parameters between carbon/phenolic material and C/C material of nozzle,heat exchange occurs at the interface.The heat is transferred from the carbon/phenolic material to the C/C composite material at the surface,and the at the internal is oppsite,the thickness of the pyrolytic layer of the carbon/phenolic material is relatively large near the interface.In this paper,the numerical simulation methods and numerical results of the heat transfer and ablation characteristics of composite structure nozzles have certain reference significance and engineering application value for the thermal protection design of nozzles.