Study On Thermal Protection Mechanism And Vortex Method For Flow Past Ablation Blunt

The weapon system and spacecrafts flying in a harsh environment are generally coupled with extreme high temperature, high overload, high heat flux and strong erosion. Especially, the successful test flight of X-37B lead a new competition of near space weapons among world military powers, which puts the flight environment to a harsher level and makes the material behavior more complex. The thermal protection mechanism and relative simulation theory under extreme environment are the basis of establishing a material evaluation platform, as well as the premise of revealing the nature of materials failure. Currently, experiments under extreme environment cannot reflect the whole ablation process and there is still a gap between simulation and the real situation, so it's urgent to develop a new simulation theories and relative numerical method.The objection of this dissertation is to reveal the thermal protection mechanism of spacecraft on basis of multi-disciplinary theories and improve the vortex method which is used to solve the flow field; based on these, the nonlinear analysis can be carried out by taking the gaseous mixture flow past an ablating cylinder for an example. This study may provide theoretical basis for simulation characterization and optimization on thermal protective performance of near space crafts.The main research results are as follows:(1) Several mechanisms of thermal protection are studied. Firstly, a concept of'zero linear ablation'is presented for modifying'non-ablation'based on material science and heat transfer theory with the assumption of oxidation reaction can be neglect; Then the heat conditions of several materials are inversed when'zero linear ablation'is satisfied; and the thermal response of some self-transpiration material is also obtained which avoids the unreasonable re-pyrolysis in commercial software. Conclution can be drawn that both the thermo-physical attributes of thermal protection material and the thermal environment determinate'non-ablation'; the 'zero linear ablation'of self-transpiration material has a close relationship with heat flux, diaphoretic content and heating time, the'zero linear ablation'of aluminizing carbon only appears in low heat flux environment.(2) On basis of thermo-chemistry and materials physics, two thermal analysisi models of SiO2/P are given acoording to the contents of SiO2 with the zero linear ablation and linear ablation examples; an ablation model is proposed for calculating the ablation rate of a solid rocket nozzle throat which is making up of carbon fiber reinforced carbon matrix composites. From this model, a distinguishing method is put forward for determining the ablation control mechanism, and the relative software is also developed with a mixed programming technique; additionally, we talked about the affecting factors on ablation rate such as temperature and pressure of gaseous mixture in rocket engine, hydrogen concentration, activation energy and frequency factor. As indicated from the results, hydrogen concentration and activation energy may alter the ablation mechanism.(3) A Lagrange vortex method is developed. When solving the viscosity equation, the core spreading vortex method(CSVM) and particle strength exchange(PSE) method are advised to be used together, that is to simulate the vorticity by using CSVM near the boundary, whereas the PSE is adopted far away from the boundary; For the convection equation, the computational efficiencies between the N body method and the fast multipole expansion method (FMM) are compared, some examples are solved by using a Fortran/Matlab codes written with the newly proposed reverse quadtree adaptive grids technique. From the results we know, FMM performs better than the N body method, and the reverse quadtree adaptive grids technique may improve the efficiency of FMM; compared with former achievements, the improved vortex method gets a high performance, which may get smoth curves of boundary vorticity, high resolution vorticity contour and drag coefficient even in the case that the boundary is divided into less panels.(4) The compressible vortex method is primarily explored, the 2D viscosity unsteady compressible governing equations are given, which is expressed by vorticity, dilatation, density entropy and enthalpy, and the evolutions of vorticity and density under different Mach number are also studied in cases of symmetric and asymmetric.(5) Based on the theories of vorticity, ablation and chaos, works are carried out on simulation of the model built for solving the gaseous mixture flow past an ablating cylinder in a high temperature and high pressure environment and relative chaos indentification. Being different from the stable changes of the flow past a non-ablation cylinder, the drag and the lift coefficient curves have severe shocks when gaseous mixture flow past an ablating cylinder. The gaseous mixture flow past an ablating cylinder can be seen as a process changing from order to chaos, then to noise.