【作者】 徐晓亮；

【导师】 章梓茂； 黄海明；

【作者基本信息】 北京交通大学 ， 工程力学， 2011， 博士

【摘要】 武器系统以及航天飞行器往往在超高温、高过载、高热流、强侵蚀等多项恶劣因素耦合的环境下工作；特别值得关注的,美国X-37B试飞的成功引起世界强国在近空间武器方面的争夺,导致飞行器服役环境愈加严酷,材料的行为及其变化非常复杂。极端环境下热防护机理与模拟理论是建立材料性能考核平台的理论基础,也是搞清这种环境下材料失效本质的前提；目前极端环境试验方法尚不能全过程地反映环境与材料的相互作用,模拟与真实情况之间还存在一定的差距,急需发展热防护理论与模拟方法。基于烧蚀学、材料学、计算流体动力学等多学科理论,本文分析了飞行器的几种热防护特例的机制,发展了涡方法,并对烧蚀圆柱绕流进行了非线性分析；为近空间飞行器热防护性能模拟表征与优化设计提供了理论依据。本文的主要研究成果有：(1)提出“零线烧蚀”,发展了“无烧蚀”概念；并开发了给定流场压力条件下热沉/辐射、发汗类材料零线烧蚀的反演软件,避免了商业软件中反复热解的不合理性,反演得到了零线烧蚀的极限条件。结果表明：无烧蚀是由材料的热物理属性与热环境共同决定,给出了几种无烧蚀防热材料(不考虑氧化)的许用时间表；炭渗铝发汗材料零线烧蚀仅适用于低热流情况。(2)基于热化学、材料物理学等理论,分析了SiO2/P复合材料(酚醛低含量、高含量两种)烧蚀及炭/炭喉衬的烧蚀,并提出了一种烧蚀控制机制判别方法,开发了固体火箭喷管喉衬烧蚀计算软件。(3)基于涡运动理论,发展了一种拉格朗日型流场计算的涡方法；在快速多极子展开法的基础上提出了一种逆向四叉树自适应网格划分技术；利用Fortran/Matlab联合编程分析了几个经典算例。结果表明：逆向四叉树划分技术提高了快速多极子展开法的效率；与已有的成果相比,本文所设计的粘性方程求解方法更加高效,即使将绕流边界划分为较少数量的平板,依然可以快速地得到光滑的边界新生涡和阻力系数曲线以及高精度的涡量云图和流场速度分布。(4)初步探索了涡方法向可压缩流场拓展的问题。给出了以涡量、胀量、密度、熵和焓为基本未知量的二维粘性非稳态可压缩控制方程组,在不同马赫数条件下探讨了对称、非对称旋涡对运动过程中涡量场与胀量场的演化规律。(5)基于涡运动理论、烧蚀理论和混沌理论,建立了烧蚀钝体绕流的数理模型,将涡方法应用于烧蚀绕流分析,对高温高压环境下圆柱的烧蚀与绕流耦合问题进行了数值模拟,并做了混沌识别分析。结果表明：在流场启动初期,烧蚀引起的圆柱外形尺寸改变很小,且流场中涡元还比较少,烧蚀圆柱与无烧蚀圆柱的涡量场并无明显差异；烧蚀圆柱流场的演化要远快于无烧蚀圆柱,旋涡脱落也早于无烧蚀圆柱；烧蚀、无烧蚀圆柱的阻力系数与升力系数演化趋势相同；无烧蚀圆柱的阻力系数、升力系数趋于稳定；随着烧蚀圆柱直径的不断减小,其阻力系数、升力系数震荡剧烈,非线性特征明显；圆柱的绕流与烧蚀是一个从有序到混沌、从混沌到噪声的过程。更多还原

【Abstract】 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.更多还原