Study On Ablation Characteristics Of Solid Rocket Ramjet Insulation Under Complex Thermomechanical Loadings

During the long time working of solid rocket ramjet,the thermal environment of the afterburning chamber is very bad.There are high temperature and complex asymmetric flow,eddy current,particle erosion,mechanical erosion,thermochemical ablation,and so on.Nitrile rubber-based insulation material has the advantages of good ablation resistance,excellent adhesive performance,good mechanical properties,anti-aging performance,and good process performance.It is widely used in various models.In our missile weapons.Based on the research background of solid rocket ramjet afterburning chamber insulation,this paper studies the thermal ablation characteristics of the insulation under complex thermal load conditions deeply analyzes the two-phase flow characteristics in the afterburning chamber,carries out the experimental research on the thermal ablation of the insulation material,establishes the ablation calculation model of the insulation material,develop the corresponding heat transfer ablation calculation program,and deeply studies the long-term heat transfer characteristics The ablation characteristics of thermal insulation materials in the secondary combustion chamber of solid rocket ramjet under time operation provide an important reference value for the thermal protection structure of solid rocket ramjet.（1）The two-phase flow field in the secondary combustion chamber of a solid ramjet with a two-dimensional inlet was numerically simulated,and the flow characteristics and thermal load parameters of the adiabatic layer were obtained.The results show that the primary gas jet deflects downward due to the impact of airflow,and the flow field area is divided into the upper low temperature oxygen rich area and the lower high temperature oxygen poor area along the axial direction.With the increase of air-fuel ratio,the low-temperature oxygen rich zone expands to the center of the flow field,and the high-temperature oxygen poor zone gradually approaches the head of the afterburning chamber.（2）The ablation process,ablation structure,and thermal decomposition characteristics of NBR based thermal insulation materials were studied by laser ablation carbonization experiment,thermogravimetric analysis,and scanning electron microscope.The results show that the ablative structure of the thermal insulation material is divided into three layers:the original layer with a compact structure,the pyrolytic layer with thermal decomposition reaction,and the porous carbonized layer.The ablative surface is attached with a gray-white surface formed by Si O₂.The thermal decomposition kinetic parameters of the insulation material were obtained by thermogravimetric analysis.（3）Aiming at the ablation process of the rubber-based thermal insulation material,an ablation model of the material density,specific heat capacity,thermal conductivity,and porosity with time and temperature was proposed,and the thermochemical ablation effect was considered.The calculation program of thermochemical ablation was developed with the FORTRAN language.The reliability and accuracy of the program are verified through two heat conduction calculation examples and comparison with the classical ablation experimental results,which provides a solution platform and theoretical basis for simulating the ablation process of the insulation in the afterburning chamber.（4）According to the two-phase flow field characteristic parameters and thermal load parameters obtained from the simulation,the ablation process of the thermal insulation under different calculation models is studied by using the variable thermal physical property ablation calculation program.The influence of thermal load parameters on the ablation process of the thermal insulation and the ablation situation of the thermal insulation under different air-fuel ratios are analyzed.The results show that the thermal insulation performance of the model with variable thermal properties is better than that of the model with constant physical properties,and the diffusion speed of heat in the insulation is accelerated by thermochemical ablation.The higher the heat flux is,the greater the ablation is.The effect of O₂ concentration is very small in the low temperature region,but it is very big in the high temperature region.The increase of O₂concentration will increase the ablation of the insulation,while the effect of CO₂,H₂O concentration,and gas pressure is very small.The results show that the ablation amount of the low temperature oxygen rich zone is lower than that of the high temperature oxygen poor zone in the afterburning chamber,and the high temperature zone in the front section of the inlet and the rear section of the afterburning chamber have higher ablation amount.The ablation amount of the high temperature region in the front section of the inlet increases with the increase of the air-fuel ratio,while the ablation amount of the high temperature region in the back section of the afterburner decreases with the increase of the air-fuel ratio.