Aerodynamic heating seriously affects the safety of hypersonic vehicles, which is an urgent problem to be solved. In this work, an aerothermal phase change thermal protection system using foam structure arranged inside aircraft skin is put forward. Firstly, considering the characteristics of aircraft skin, the three-dimensional foam structures, with and without skeleton micropores, is reconstructed. Then, the effects of liquid water mass flow rate and micropores in the foam structure on heat and mass transfer in the aerothermal phase change thermal protection system are investigated. Results show that the aircraft skin temperature decreases fast and then slowly to a platform, with an increase in liquid water mass flow rate. The heat transfer in the foam structure also increases fast and then slowly to a platform, with an increase of liquid water mass flow rate, while the pressure drop for the foam structure increases linearly with an increase in liquid water mass flow rate. The comprehensive heat transfer performance of liquid water flowing along micropores is better than that of liquid water flowing without micropores and vertical to the micropores. The discovery of the above phenomenon helps design a good aerothermal phase change thermal protection system.

An ablation model considering reaction kinetics of carbon interphase in carbon/carbon composites is proposed. The proposed model also comprehensively considers the couple of the oxygen diffusion, the movement and reaction heat at the carbon-air interface, the aerodynamic heat on the ablation layer, and the heat conduction in the carbon solid. The pre-exponential factor and the apparent activation energy in the Arrhenius formula is put forward. Simulated ablation morphologies agree well with experimental results. The aerodynamic heat accelerates the formation of reaction morphology. The apparent activation energy coefficient has a greater effect on reaction morphology compared with the pre-exponential factor coefficient.

The thermal management systems or heat sinks are an integral part of electronic devices for aerospace applications. The heat transfer characteristics of the widely used phase change material (PCM)-based heat sinks under hypergravity conditions are essential in the designation of the heat sink. The current study conducts a systematic evaluation on the thermal characteristics of PCM coupled with hybrid fin-metal foam (FMF) structure under variable hypergravity conditions. A validated two-dimensional transient melting heat transfer model of the designed system is proposed, and the influences of enclosure orientation, fin height, PCM slab thickness, and the distribution of fin and metal foam under different hypergravity conditions are investigated. Results show that with the decrease in inclination angle, the melting time and the heating wall temperature become lower, and the optimal inclination angle is 0°. As the PCM slab thickness gets larger, natural convection is enhanced, while the heating wall temperature and melting time become larger. With the rise of hypergravity value, the effect of inclination angle strengthens, while the influence of PCM slab thickness weakens. Furthermore, with the rise of the copper foam fraction in the hybrid FMF structure, the melting time and the heating wall temperature firstly decrease and increase afterward. The optimal copper foam fraction is 58.62%. This study guides the optimal design of the PCM-based heat sink in aerospace applications.

Designing an accurate and efficient heat protection system for the area around the high-temperature stagnation point on supersonic aircraft is still an important topic of research. In the present study, a three-dimensional high thermal conductivity carbon/carbon (C/C) composite thermal protection system embedded with L-shaped carbon fiber bundles for directional heat transfer is proposed as a high-efficiency thermal protection design. A multi-scale method, which couples the finite volume method (FVM) and lattice Boltzmann method (LBM), is developed to investigate the directional heat transfer in the proposed structure. The FVM is used to calculate the heat radiation information, which is needed to solve the energy equation with the LBM. Further, the failure temperature of the proposed thermal protection structure is defined. The effects of the porosity, carbon fiber bundle and pore diameter on the directional heat transfer of the L-shaped C/C composite thermal protection system are investigated in detail. The results show that the effective thermal conductivity of the proposed thermal protection system increases with increasing temperature and carbon fiber bundle diameter. It decreases with increasing porosity when the temperature is below 1000 degrees C. There exists the competitive relationship between the pore heat radiation and carbon fiber bundle thermal conductivity. An increased porosity results in a decrease in the failure temperature of the proposed thermal protection structure, while increasing the carbon fiber bundle diameter can increase the failure temperature. These findings can provide some new insights for designing a high-performance C/C composite thermal protection system.

There are more and more researches on heat transfer characteristics and prediction of supercritical CO 2 .The method of adding adiabatic section before and after heating section is usually adopted in these researches to ensure that the fluid entering the heating section is no longer affected by boundary layer,but the appropriate length range of adiabatic section and the influence of entrance effect are not discussed.However,some studies show that the entrance effect would affect the heat transfer in mini tubes.This paper uses the commercial CFD code FLUENT 19.0 to numerically study the heat transfer of supercritical CO 2 in a mini tube under different working conditions(such as Re in ,P in ,q w and flow direction) and the lengths of the adiabatic section(l as /d).The entrance effects on heat transfer is more pronounced when Re in is within the transition state and wall heat flux is relatively high,the resulting heat transfer deterioration causes T w,x and h w,x to rise sharply.As the adiabatic section increases,the location at which the heat exchange deteriorates moves to the entrance of the heating section and eventually leaves.The buoyancy effect and flow acceleration effect caused by the sharp change of physical properties are analyzed,and the dimensionless velocity distribution at the inlet of the heating section in different adiabatic sections is compared.It is proved that the entrance effect has an influence on the convection heat transfer of supercritical CO 2 in mini tubes.The interaction reflected by wall shear stress between boundary layer development and drastic changes in physical properties is the cause of heat transfer deterioration.

通过加强对装备环境适应性的闭环管控,避免设计方案反复,提高研制效率和装备环境适应性.在系统工程方法基础上,建立装备环境适应性闭环管控工作体系,提出闭环管控方法,包括基于流程前置的环境工程工作计划,面向流程闭环的环境适应性工作过程控制,以及全寿命周期环境适应性信息管理等内容.装备工程实践结果表明,提出的环境适应性闭环管控方法是可行的,环境适应性问题早在方案设计阶段即得到了有效解决,使环境适应性工作变被动为主动,在提高装备研制效率的同时,提升了产品的环境适应性.该方法可以有效提高装备环境适应性和研制效率,对于运载火箭、航天器、工业设备等其他类型产品的研发也有一定的借鉴意义.

The thermal performance of phase change materials (PCM) embedded with fins and metal foam is investigated. Plate fins are attached to the enclosure, and metal foam is embedded between adjacent fins to enhance heat transfer. To predict the melting behavior, a numerical model is established based on the enthalpy-porosity method, considering natural convection, flow resistance induced by metal foam, and non-equilibrium heat transfer. Nine cases considering various geometric parameters, heat transfer enhancement designs, and heated wall temperature are studied. Furthermore, a dimensionless theoretical model is derived to conclude the effect of combined parameters. It shows that the melting time reduces by 24.8 % as the fin height decreases from 80 mm to 50 mm, and the melting time becomes shorter with the decrease of fin thickness. However, the heat flux gets higher for higher fin height and thinner fin thickness. Moreover, the melting rate and heat flux become higher for higher fin volume fraction, lower metal foam porosity, and higher heated wall temperature. Furthermore, the theoretical model reveals that as Stefan number, fin efficiency, and the ratio of thermal diffusivity to the squared fin height become larger, the melting rate becomes higher.

碳/碳(C/C)复合材料具有热导率大、比强度高、耐烧蚀和耐冲刷等优异特性,被广泛应用于飞行器的热防护系统中,其有效导热系数对于实际应用而言是重要的热物理性质,尽管可以通过有效介质理论、对热扩散方程直接求解和玻尔兹曼输运方程等传统方法计算C/C复合材料有效导热系数,但这些数值方法通常十分耗时.本文引入深度学习方法,将格子玻尔兹曼(LBM)的三维格子模型作为三维卷积神经网络(3D-CNN)微观结构,不仅解决了三维微观结构模型难以捕获的问题,还便于实现数值计算模型和CNN模型的同步简化,利用3D-CNN快速精准地预测三维三相C/C复合结构的有效导热系数,基于此对内置L型高导热碳纤维丝的定向热疏C/C复合结构的有效导热系数进行快速预测和研究.研究表明,CNN模型在LBM传热计算上表现出强大的学习能力,但在测试样本结构孔隙率过分超出训练集时预测误差将大幅增加,且当孔隙率变化范围从30％～35％变化到55％～60％时,CNN模型"内插"预测的相对误差较模型"外推"降低了0.93％～30.72％.在C/C复合结构中内置L型高导热碳纤维丝可以将高温区域的热量沿纤维方向定向疏导至低温区域.

多层热防护结构由防热层与隔热层等多层热防护材料组成,在气动热作用下存在复杂的烧蚀与传热过程.为准确预示多层热防护结构温度响应特性,建立了气动热环境下防热材料烧蚀模型,提出了烧蚀导致的变厚度多层结构传热数值计算方法,研究了气动热环境下多层热防护结构温度分布随时间变化规律,分析了多层热防护结构厚度分布对防热效果的影响.研究表明,提出的模型能准确预示多层热防护结构烧蚀与传热过程,热量传导至承力结构后,隔热层内温度梯度大于防热层内温度梯度,在满足隔热层温度、烧蚀裕度以及工艺要求前提下,增大隔热层厚度能提高热防护性能.

针对航天飞行器多组件式机械分离装置的分离临界力不可测量以及多组件装配、工艺不确定性影响分离可靠性的问题,利用感度试验原理设计基于组件互换及交叉组合的可靠性试验方法.结合试验数据特点,利用广义线性模型描述了分离可靠性与分离力的关系,对分离装置可靠性进行了评估.试验结果表明,该方法可在子样有限的情况下对多组件式机械分离装置可靠性进行有效评估.

The thermal performance of a flat plate latent heat storage unit (LHSU) consisting of parallel flat plate slabs of phase change material (PCM) was investigated with analytical techniques. The approximate analytical expressions of the heat transfer fluid (HTF) transient temperature distribution and the time wise solid-liquid PCM interface location were developed by solving the energy conservation equations and were validated by comparing the present results with fully converged numerical predictions and analytical solutions in published literature. An index of effective latent heat storage ratio, E-r, which was defined as the ratio of the actual amount of available latent thermal energy before HTF outlet temperature reaches a specified value to the total latent heat storage capacity, was proposed to evaluate the thermal performance of a LHSU. The effects of geometric parameters and the thermal conductivity of PCM (k(r)) on E-r were investigated. The results show that the analytical model is valid as the Stefan number is less than 0.15. Moreover, E-r increases with the rise of the given dimensionless HTF outlet temperature and the enhancement of k(p), and decreases linearly with the increase of HTF channel height and PCM slab thickness, with an abrupt change in the derivative of E-r at an inflection point. A dimensionless criterion was proposed to help design thermally efficient flat plate LHSU. Additionally, we found that increasing PCM mass by lengthening the PCM slab could significantly improve E-r, while thickening the PCM slab would lead to the opposite trend. This investigation provides guidelines for the optimal design of a flat plate LHSU.

目的 分析舰载武器在海洋自然环境下的失效模式.方法 对舰载武器装备全寿命周期环境剖面进行分析,经过梳理确认与海洋自然环境有关的任务剖面.以提高产品海洋自然环境适应性和可靠性为目标,设计海洋自然环境试验,根据产品实际使用所处的海洋自然环境,确定参试产品投放的位置为远海库内和平台库内.根据产品的组成,确定失效模式分析的对象,给出了失效模式分析的流程.结果 基于试验结果,给出了舰载武器在海洋自然环境下的4种失效模式.结论 舰载武器在海洋自然环境下的典型失效模式,包括单机壳体表面金属材料生锈、单机产品表面涂漆气泡、活动部件迟钝及接插件表面锈蚀等.

Aiming at reliability design for electronic devices, process neural networks are proposed to predict the temperature of electronic devices. To avoid errors caused by discrete input data fitting or difference, only discrete data is used when solving orthogonal transformation coefficients. To accelerate the learning speed of the gradient descent algorithm, a parameter- independent adaptive learning algorithm is developed. The results show that this model has better accuracy and generalization ability compared with artificial neural networks and linear regression method, and the parameter-independent adaptive learning algorithm has quicker convergence rate compared with parameter-fixed algorithm and adaptive learning algorithm.

An accurate model is very important for thermal prediction and thermal management of airborne electronic module. Thermal Network Model (TNM) is the commonly used to analyze transient thermal response. It cannot describe the nonlinear or time-varying temperature process very well. In order to realize a fast thermal modeling with a relatively high accuracy, this paper proposes a modeling method based on sliding time window Random Vector Functional Link Neural Network (RVFLNN). The input and output variables of RVFLNN are determined by analyzing the heat transfer relationship of studied system. This method can rapidly realize thermal modeling without a time-consuming iterative training process. In order to overcome the variability of studied system, the sliding time window technology is specially introduced to improve the model prediction accuracy. This method is applied to analyze thermal experimental data of electronic equipment cabin. The temperature prediction performance of presented method is compared with the traditional Artificial Neural Network Model (ANNM). Comparison results show that the proposed modeling method has the advantages of fast modeling and good prediction accuracy. This study can provide an effective way to describe a complex dynamic heat transfer process adaptively and accurately, which may help the thermal control scheme design.

This study presents the optimization of the geometry of pin-fin heat sink with un-uniform fin dimensions. A procedure is presented to find the optimum geometry of pin-fin with un-uniform fin heights and widths. It is concluded that the highest temperature is lower and the temperature gradient is smaller in the optimum geometry, and the fin heights and widths near the central part of the heat sink are higher and wider than the fins at the edge. As the total volume of fins increases, the entropy generation decreases while the decreasing rate slows down.