Ablation Investigation Of C/SiC Composite Material In Scramjet

The thermal protection is very important to the development of scramjet technology. Theablation performance can evaluate and measure the thermal protection and affect workperformance and service life of the engine structural elements. C/SiC composite material is anew type of strategic materials, with low density, high temperature resistance, high specificmodulus, high specific strength, low brittle, anti-ablation, anti-oxidation and high reliability.It’s ideal material of the thermal protection and thermal structure for scramjet. However,Engineering calculations lack ablation models and methods, so this thesis conducts study onthe subject.Based on the analysis of the ablation mechanism, erosion and mechanical denudation canbe ignored in the condions of this thesis, material occur mainly thermochemical ablation, andactive oxidation of SiC is mostly occured in main ablation areas. Comprehensive consideringthe influence of temperature, pressure, oxidizing component （O₂and H₂O） concentrations,this thesis has build thermochemical abalaton models for oxygen without water vapor andoxygen with water vapor conditions. The fluidity numberical simulation of experimental ductagree well with test results, which uses Plasma wind tunnel to heat the air（with water） forC/SiC flat ablation test. Used the flow field parameters of C/SiC flat wall as boundaryconditions, brought it into the ablation program code to calculate the steady-state materialablation. The ablation thickness computed result of C/SiC flats specimens agrees with theexperiment result in some degree. But, because of the impact of non-stationary processes andmaterials deformation, the Ablation thickness distribution of Parts C/SiC flats specimensdidn’t fit for the experiment result. For C/SiC flats specimens which were less affected bythese two factors, the average relative error of ablation thickness in main ablation areas are10.2%and7.4%. It means that this ablation model and calculation methods can predict theablation thickness degree of C/SiC composite material to a certain extent. Laid the foundationfor ablation calculations of C/SiC composites material in scramjet and thermal protectiondesign.It shows that the ablation thickness increases with the increase of Wall temperature,pressure, oxidizing component （O₂and H₂O） concentrations or adjunction of other oxidizingcomponents by quantitative analysis of the impact for ablation of these four factors. When the temperature is below1600K, the ablation is very slight; when the temperature is between1600K and1900K, the ablation thickness increases relatively slowly; and when thetemperature is higher than1900K, the ablation thickness increases relatively fast with seriousablation. With the increase of pressure or H₂O concentrations, the ablation thickness increasesapproximate in parabolical change law; and with the increase of O₂concentrations, theablation thickness increases approximate in linear change law.This thesis also has carried out preliminary calculations of C/SiC composite material inscramjet wall of the main combustion zones. The computed results show that the bottom wallablated seriously, the most serious positions are at the bend of the rear of the trailing edge ofthe cavity, and the maximum ablation thickness is4.7mm in60seconds. The distribution ofablation thickness is similar to the distribution of wall temperature. The analysis show that athigher temperature and pressure conditions, with the decrease of O₂concentration andincrease of H₂O concentration caused by the burning of kerosene, the ablation thicknessdecreases. So the serious ablation caused by high temperature with the burning of keroseneand the release of heat can be Mitigated, and this change law is good for the thermalprotection of scramjet.