变密度炭化复合材料的热防护模型及其数值模拟
发布时间：2018-08-25 08:21
【摘要】：航天器返回舱穿越地球大气层飞行时受到严重的气动加热,为了克服由于气动加热造成的"热障",对返回舱进行热防护是必不可少的。根据返回舱再入大气层时的环境特点,即高比焓、低热流密度、低压、低剪力和较长的再入时间,通常选用炭化复合材料作为热防护材料。针对急剧变化的航天器服役环境,均匀密度炭化复合材料的热防护效率比较低,因此,变密度炭化复合材料的设计是热防护系统发展方向。本文基于传热学、物理化学、气动热力学、燃烧学、数值传热学、数值分析等理论,开展变密度炭化复合材料的热防护模型及其数值模拟研究。基于炭化复合材料烧蚀机理,假设热解反应均发生在热解面上,发展了变密度炭化复合材料的一维热解面模型。根据传热学理论,对原始材料层与炭化层分别建立一维瞬态傅里叶热传导方程,方程中热物理性能参数是密度或密度与温度的函数;在移动的热解面处建立温度连续条件与热解能量守恒条件;在烧蚀表面处建立能量守恒关系,它与表面烧蚀率相关,而碳的氧化烧蚀率是壁面温度的函数。基于数值传热学方法,利用二阶中心差分格式和一阶向前差分格式分别对静态坐标系下变密度炭化复合材料导热偏微分方程中的空间项和时间项进行离散,获得隐式的离散格式。针对带有移动边界与移动界面的离散格式,提出一种新的非线性计算方法:利用上一时刻的结果确定材料总厚度、原始材料层厚度与炭化层厚度,更新空间节点及热解面节点,利用三对角阵算法和牛顿迭代法对当前时刻的隐式离散格式进行求解;利用当前时刻的温度,由烧蚀表面温度及烧蚀率的函数求得烧蚀表面移动距离,由不动点迭代法求得满足热解面能量守恒条件的热解面移动距离。将上述计算方法通过MATLAB编程实现,进一步分析了在常热流作用下均匀材料的热响应以及在变热流作用下均匀与变密度材料的热响应。数值结果表明:变密度炭化复合材料热解面模型可以应用于求解均匀密度炭化复合材料的烧蚀及热响应;变密度炭化复合材料具有更高的有效热熔,能够提高热防护系统的防热效率。为了更能精确地反映炭化复合材料的热响应,建立变密度炭化复合材料的一维热解层模型,其特点:在炭化层与原始材料层之间的热解层中既有热解反应又有热解气体流动,热解反应导致热解层的密度不断变化,热解层的热物理性能是密度与温度的函数。在该模型中,除了原始材料层和炭化层的控制方程、烧蚀表面边界条件分别与热解面模型的相同之外,增加热解层的瞬态热传导方程,两个内部移动界面的温度与热流连续条件。为了简化计算,热解层的密度与热物理性能参数做线性处理。利用热解面模型的离散方法,对热解层数学模型构造其隐式的离散格式。针对带有移动边界和双移动界面的非线性离散方程组,发展新的求解方法:利用上一时刻的结果确定材料总厚度、原始材料层厚度、热解层厚度与炭化层厚度,划分空间节点,更新移动界面节点,采用三对角阵算法和牛顿迭代法对当前时刻的隐式离散格式进行求解;由烧蚀表面温度及烧蚀率的函数确定烧蚀表面移动距离,由牛顿弦截法确定满足热流连续条件的内部双界面移动距离。基于MATLAB平台,利用上述求解方法对隐式的离散格式进行编程,计算分析了均匀材料在常热流作用下的热响应、均匀材料和变密度材料在变热流作用下的热响应,以及对比分析了均匀材料在常热流作用下热解面模型与热解层模型的计算结果。数值结果表明:通过对均匀材料热解层模型的数值计算结果与前人的试验结果对比,验证了所建立的热解层模型可以应用于求解均匀材料的热响应;在服役过程中,变密度热防护层烧蚀表面上的有关参数(温度、烧蚀率、热解气体质量流率)及各层厚度不仅与气动热流有关,还与材料密度分布息息相关;变密度材料具有较高的有效热熔,能够提高热防护系统的防热效率;经过两个模型的对比,发现热解面温度的选取对热解面模型的计算精度至关重要。上述两个模型中均假设表面烧蚀率为温度的函数,未考虑热解气体在激波层内的燃烧反应对材料表面烧蚀的影响。为了精确分析材料表面的烧蚀率,基于热解气体燃烧的层流流动假设,利用气动热力学、传热学、燃烧学、物理化学等理论,建立炭化复合材料的热-流-化学-烧蚀多场耦合模型,该模型包含:正激波方程组、热解层数学模型、热解气体的对冲扩散燃烧模型以及材料表面氧化烧蚀模型,并提出了"开始反应面"与"临界速度"概念。利用拟牛顿法通过编写FORTRAN代码求解非线性正激波方程组获得正激波后气体温度和流速;利用热解层模型的计算方法,求得烧蚀表面上的温度和热解气体流速;将求得的结果作为对冲扩散燃烧模型的边界条件,利用OPPDIF程序求解热解气体的对冲扩散燃烧模型,获得烧蚀表面附近的氧气质量分数;把氧气质量分数和烧蚀表面温度等参数代入材料表面氧化烧蚀模型,利用MATLAB平台编程计算获得表面烧蚀率;再把求得的烧蚀率代入热解层模型中,重复上述计算步骤,直至表面烧蚀率的迭代误差满足精度要求,便可确定当前时刻的表面烧蚀率。基于C++、MATLAB及ACCESS等计算机语言,开发出一套高超音速气动热环境下炭化复合材料热防护仿真软件。借助该软件平台,分析激波层内热解气体燃烧反应对材料表面烧蚀的抑制作用。数值结果表明:热解气体的燃烧反应在一定程度上抑制了炭化复合材料表面的烧蚀速率,但对材料内部温度场影响不大。
[Abstract]:In order to overcome the "thermal barrier" caused by aerodynamic heating, it is necessary to provide thermal protection for the spacecraft's reentry capsule. According to the environmental characteristics of the reentry capsule, such as high specific enthalpy, low heat flux, low pressure, low shear force and long reentry time, it is usually selected. Carbonized composites are used as thermal protection materials. The thermal protection efficiency of uniform density carbonized composites is relatively low in the rapidly changing spacecraft environment. Therefore, the design of variable density carbonized composites is the development direction of thermal protection systems. Based on the ablation mechanism of carbonized composites, assuming that all the pyrolysis reactions take place on the pyrolysis surface, a one-dimensional pyrolysis surface model of variable density carbonized composites is developed. According to the theory of heat transfer, the original material layer and carbonized layer are built separately. A one-dimensional transient Fourier heat conduction equation is established in which the thermophysical parameters are a function of density or density and temperature; a temperature continuity condition and a pyrolysis energy conservation condition are established at the moving pyrolysis surface; and an energy conservation relation is established at the ablated surface, which is related to the ablation rate of the surface, while the ablation rate of carbon is a function of the wall temperature. Based on the numerical heat transfer method, the space and time terms of the partial differential equation of heat conduction for variable density carbonized composites in static coordinate system are discretized by using the second-order central difference scheme and the first-order forward difference scheme respectively, and an implicit discrete scheme is obtained. A new non-linear calculation method is proposed, which uses the results of the previous time to determine the total thickness of material, the thickness of original material and the thickness of carbonization layer, updates the spatial nodes and pyrolysis surface nodes, and uses the tridiagonal matrix algorithm and Newton iterative method to solve the implicit discrete scheme of the current time. The moving distance of the ablation surface is obtained by the function of ablation rate, and the moving distance of the pyrolysis surface satisfying the energy conservation condition of the pyrolysis surface is obtained by the fixed point iteration method. The numerical results show that the pyrolysis surface model of variable density carbonized composites can be used to solve the ablation and thermal response of uniform density carbonized composites; the variable density carbonized composites have higher effective hot melting and can improve the thermal protection efficiency of the thermal protection system. In order to reflect the thermal response of the carbonized composites more accurately. A one-dimensional pyrolysis layer model of variable density carbonized composites was established. The pyrolysis reaction and gas flow were found in the pyrolysis layer between the carbonized layer and the raw material layer. In order to simplify the calculation, the density and thermophysical parameters of the pyrolysis layer are linearly treated. The dissociation of the pyrolysis surface model is used. An implicit discrete scheme is constructed for the mathematical model of pyrolysis layer. A new method is developed for solving the nonlinear discrete equations with moving boundary and double moving interface. The total thickness of material, the thickness of raw material, the thickness of pyrolysis layer and the thickness of carbonization layer are determined by the results of the previous time, and the spatial nodes are divided and the moving boundary is updated. The implicit discrete scheme is solved by using tridiagonal matrix algorithm and Newton iteration method at the current moment. The moving distance of the ablation surface is determined by the function of the ablation surface temperature and ablation rate, and the moving distance of the internal two interfaces satisfying the condition of continuous heat flow is determined by Newton chord cut method. The implicit discrete scheme is programmed to calculate and analyze the thermal response of homogeneous materials under constant heat flux, homogeneous materials and variable density materials under variable heat flux, and the results of the pyrolysis surface model and the pyrolysis layer model of homogeneous materials under constant heat flux are compared and analyzed. Comparing the numerical results of the pyrolysis layer model with the experimental results, it is verified that the pyrolysis layer model can be used to solve the thermal response of homogeneous materials; in the course of service, the parameters (temperature, ablation rate, mass flow rate of pyrolysis gas) and the thickness of each layer are not only related to the aerodynamic heat. It is found that the selection of pyrolysis surface temperature is very important to the calculation accuracy of the pyrolysis surface model. Both models assume that the ablation rate is a function of temperature. In order to accurately analyze the ablation rate of the material surface, based on the laminar flow hypothesis of pyrolytic gas combustion, the thermo-hydro-chemical-ablative multi-field coupling of carbonized composites was established by using the theories of aerothermodynamics, heat transfer, combustion and physical chemistry. The model consists of forward shock equations, pyrolysis layer model, pyrolysis gas combustion model and material surface oxidation and ablation model. The concepts of "starting reaction surface" and "critical velocity" are proposed. The gas temperature after forward shock is obtained by writing FORTRAN code to solve nonlinear forward shock equations. The temperature on the ablated surface and the velocity of pyrolytic gas were calculated by using the pyrolytic layer model, and the results were taken as the boundary conditions of the contra-diffusion combustion model. The contra-diffusion combustion model of pyrolytic gas was solved by OPPDIF program, and the oxygen mass fraction near the ablated surface was obtained. The ablation surface temperature and other parameters are substituted into the material surface oxidation ablation model, and the ablation rate is calculated by MATLAB platform programming. Then the ablation rate is substituted into the pyrolysis layer model, and the above calculation steps are repeated until the iterative error of the ablation rate meets the accuracy requirement. The current ablation rate can be determined based on C++, M. A set of simulation software for thermal protection of carbonized composites in hypersonic aerothermal environment was developed by using computer languages such as ATLAB and ACCESS. The inhibition effect of combustion reaction of pyrolytic gases in shock layer on the surface ablation of materials was analyzed by using the software platform. The numerical results show that the combustion reaction of pyrolytic gases inhibits carbonization to a certain extent. The ablation rate of the composite surface has little effect on the temperature field inside the composite.
【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：V445.1;V25
本文编号：2202312
[Abstract]:In order to overcome the "thermal barrier" caused by aerodynamic heating, it is necessary to provide thermal protection for the spacecraft's reentry capsule. According to the environmental characteristics of the reentry capsule, such as high specific enthalpy, low heat flux, low pressure, low shear force and long reentry time, it is usually selected. Carbonized composites are used as thermal protection materials. The thermal protection efficiency of uniform density carbonized composites is relatively low in the rapidly changing spacecraft environment. Therefore, the design of variable density carbonized composites is the development direction of thermal protection systems. Based on the ablation mechanism of carbonized composites, assuming that all the pyrolysis reactions take place on the pyrolysis surface, a one-dimensional pyrolysis surface model of variable density carbonized composites is developed. According to the theory of heat transfer, the original material layer and carbonized layer are built separately. A one-dimensional transient Fourier heat conduction equation is established in which the thermophysical parameters are a function of density or density and temperature; a temperature continuity condition and a pyrolysis energy conservation condition are established at the moving pyrolysis surface; and an energy conservation relation is established at the ablated surface, which is related to the ablation rate of the surface, while the ablation rate of carbon is a function of the wall temperature. Based on the numerical heat transfer method, the space and time terms of the partial differential equation of heat conduction for variable density carbonized composites in static coordinate system are discretized by using the second-order central difference scheme and the first-order forward difference scheme respectively, and an implicit discrete scheme is obtained. A new non-linear calculation method is proposed, which uses the results of the previous time to determine the total thickness of material, the thickness of original material and the thickness of carbonization layer, updates the spatial nodes and pyrolysis surface nodes, and uses the tridiagonal matrix algorithm and Newton iterative method to solve the implicit discrete scheme of the current time. The moving distance of the ablation surface is obtained by the function of ablation rate, and the moving distance of the pyrolysis surface satisfying the energy conservation condition of the pyrolysis surface is obtained by the fixed point iteration method. The numerical results show that the pyrolysis surface model of variable density carbonized composites can be used to solve the ablation and thermal response of uniform density carbonized composites; the variable density carbonized composites have higher effective hot melting and can improve the thermal protection efficiency of the thermal protection system. In order to reflect the thermal response of the carbonized composites more accurately. A one-dimensional pyrolysis layer model of variable density carbonized composites was established. The pyrolysis reaction and gas flow were found in the pyrolysis layer between the carbonized layer and the raw material layer. In order to simplify the calculation, the density and thermophysical parameters of the pyrolysis layer are linearly treated. The dissociation of the pyrolysis surface model is used. An implicit discrete scheme is constructed for the mathematical model of pyrolysis layer. A new method is developed for solving the nonlinear discrete equations with moving boundary and double moving interface. The total thickness of material, the thickness of raw material, the thickness of pyrolysis layer and the thickness of carbonization layer are determined by the results of the previous time, and the spatial nodes are divided and the moving boundary is updated. The implicit discrete scheme is solved by using tridiagonal matrix algorithm and Newton iteration method at the current moment. The moving distance of the ablation surface is determined by the function of the ablation surface temperature and ablation rate, and the moving distance of the internal two interfaces satisfying the condition of continuous heat flow is determined by Newton chord cut method. The implicit discrete scheme is programmed to calculate and analyze the thermal response of homogeneous materials under constant heat flux, homogeneous materials and variable density materials under variable heat flux, and the results of the pyrolysis surface model and the pyrolysis layer model of homogeneous materials under constant heat flux are compared and analyzed. Comparing the numerical results of the pyrolysis layer model with the experimental results, it is verified that the pyrolysis layer model can be used to solve the thermal response of homogeneous materials; in the course of service, the parameters (temperature, ablation rate, mass flow rate of pyrolysis gas) and the thickness of each layer are not only related to the aerodynamic heat. It is found that the selection of pyrolysis surface temperature is very important to the calculation accuracy of the pyrolysis surface model. Both models assume that the ablation rate is a function of temperature. In order to accurately analyze the ablation rate of the material surface, based on the laminar flow hypothesis of pyrolytic gas combustion, the thermo-hydro-chemical-ablative multi-field coupling of carbonized composites was established by using the theories of aerothermodynamics, heat transfer, combustion and physical chemistry. The model consists of forward shock equations, pyrolysis layer model, pyrolysis gas combustion model and material surface oxidation and ablation model. The concepts of "starting reaction surface" and "critical velocity" are proposed. The gas temperature after forward shock is obtained by writing FORTRAN code to solve nonlinear forward shock equations. The temperature on the ablated surface and the velocity of pyrolytic gas were calculated by using the pyrolytic layer model, and the results were taken as the boundary conditions of the contra-diffusion combustion model. The contra-diffusion combustion model of pyrolytic gas was solved by OPPDIF program, and the oxygen mass fraction near the ablated surface was obtained. The ablation surface temperature and other parameters are substituted into the material surface oxidation ablation model, and the ablation rate is calculated by MATLAB platform programming. Then the ablation rate is substituted into the pyrolysis layer model, and the above calculation steps are repeated until the iterative error of the ablation rate meets the accuracy requirement. The current ablation rate can be determined based on C++, M. A set of simulation software for thermal protection of carbonized composites in hypersonic aerothermal environment was developed by using computer languages such as ATLAB and ACCESS. The inhibition effect of combustion reaction of pyrolytic gases in shock layer on the surface ablation of materials was analyzed by using the software platform. The numerical results show that the combustion reaction of pyrolytic gases inhibits carbonization to a certain extent. The ablation rate of the composite surface has little effect on the temperature field inside the composite.
【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：V445.1;V25
【相似文献】
相关期刊论文 前10条
1 刘啸虎;;变密度保健眼镜[J];中国医疗器械杂志;1990年03期
2 吴宝申;杨树梅;卫丕昌;;特定函数—大角度中性变密度盘的研制[J];光学机械;1992年05期
3 王春明;凌英;李瑞杰;;丁腈橡胶增韧酚醛树脂基变密度烧蚀防热复合材料研究[J];宇航材料工艺;2006年02期
4 李世荣;非均匀变密度圆形和环形薄膜的轴对称振动[J];甘肃工业大学学报;2000年02期
5 司马文霞;孙才新;张建辉;顾乐观;;变密度线电荷优化的复数模拟电荷法及其应用[J];电工技术学报;1997年01期
6 王田刚;李延娜;姚淑婷;陈叔平;王丽红;冶文莲;;变密度多层绝热最优层密度研究[J];低温与超导;2014年07期
7 石恒志，梁妍;中性变密度盘的加工与检测[J];光学技术;1994年05期
8 李世荣;连续变密度圆形和环形薄膜的轴对称振动[J];振动与冲击;2000年02期
9 张安;闫春杰;陈联;冶文莲;;基于Lockheed模型的变密度多层绝热理论分析与实验[J];真空与低温;2013年02期
10 张效慈,张军;变密度深水中的内波向水面的垂直传播[J];船舶力学;2004年01期
相关会议论文 前2条
1 马吉明;;悬臂梁与分层变密度流体的自由耦合振动[A];水电科技论文集[C];1990年
2 李伟利;;“应变密度能”强度理论的建立与应用[A];第23届全国结构工程学术会议论文集（第Ⅰ册）[C];2014年
相关博士学位论文 前2条
1 李玮洁;变密度炭化复合材料的热防护模型及其数值模拟[D];北京交通大学;2017年
2 刘茜;变密度纤维集合体的压缩、透气与隔声行为的组合表征[D];东华大学;2006年
相关硕士学位论文 前3条
1 高富强;几类变密度抽象发展方程的渐近性态[D];曲阜师范大学;2016年
2 孟红旗;变密度盘的镀制工艺研究[D];南京理工大学;2013年
3 李文祥;径向变密度球扁药制备工艺和燃烧性能研究[D];南京理工大学;2009年
，本文编号：2202312
本文链接：https://www.wllwen.com/shoufeilunwen/gckjbs/2202312.html
