高超声速非平衡流动-辐射特性数值模拟研究

飞行器高超声速飞行过程中所承受对流加热和辐射加热可能具有相当的量级,因此合理准确预测气动加热需要将二者进行综合考虑.文章发展了具有非玻尔兹曼电子能级分布和振动能级分布的高温空气碰撞辐射模型,并耦合一维激波后流动方程计算不同飞行条件下激波后的非平衡流动特性,采用逐线辐射输运模型计算获得激波后非平衡辐射特性、辐射强度和辐射输运通量,深入比较分析了不同飞行高度和马赫数对非平衡流动和辐射输运过程的影响.计算结果表明对于高空高马赫飞行条件,其波后流动存在显著的热力学非平衡、化学非平衡和能级非平衡特征,在近激波区域高振动能级和原子高束缚电子激发态明显低于玻尔兹曼分布.在高空高马赫条件下真空紫外辐射占据主导地位,主要是由高能原子束缚-束缚跃迁造成的.随着高度和马赫数的下降,激波层内气体解离和电离程度降低,原子辐射贡献下降,分子辐射贡献增加,导致红外、可见光和紫外波段的辐射输运增强,真空紫外辐射输运过程减弱.     

电磁加热条件下皮肤组织的生物热力学行为

研究目的是开发一种数学方法来计算传热过程、热引起的力学响应以及相应的疼痛等级, 从而对临床上应用的各种加热疗法之间的差别进行定量评估. 采用基于有限差分法的数值模拟方法, 基于无限大和均匀化假设, 分析了各种热疗法中皮肤组织的温度、烧伤和热应力分布. 研究发现: 充血对热损伤的影响很小, 但对皮肤的温度分布影响很大, 而这又反过来显著影响由此产生的热应力场; 对于激光加热, 光波越短则峰值温度越高, 但峰值更接近皮肤表面温度; 激光和微波加热所产生的热应力集中于表皮顶层, 因为发热量沿皮肤深度方向呈指数衰减; 薄角质层(常常被忽略)对皮肤组织的热力学响应起主导作用.      

英美板壳热应力和热屈曲研究概况

在超音速飞行中,飞机表面边界层内的空气温度由于摩擦升高很多,高温空气的热能传给飞机,使飞机表面温度昇高,称为气动加热。飞机表面各处空气的速度不同,由此而产生的表面温度分布也不均匀,飞机表面和内部结构之间则有更大的温差。飞机表面受到气动加热后要产生膨胀,而内部结构的温度较低,刚度又较大(和表面结构相比较而言),对飞机表面结构起了限制膨胀的作用。所以表面结构受到压应力,内部结构的一      

星载抛物面天线反射器瞬态热分析

星载抛物面天线反射器在周期性的冷热辐射作用下,产生不均匀的温度分布,过大的热变形严重影响卫星通信质量;采用一种8节点超参数壳单元,通过每个节点3个温度自由度表示厚度方向上温度的非线性变化,建立了单元内温度插值函数,基于Galerkin法推导出受太空冷热辐射作用的壳体结构瞬态热分析的有限元公式;运用几何解析法分析了抛物面壳体的自遮挡.对某静止轨道卫星抛物面天线进行稳态分析,与FDM结果比较表明该方法具有良好的计算精度;在不考虑地球辐射热流作用的一个运行周期的瞬态分析中,该反射器上瞬间温差达200 K,在日照区内温度变化达250 K.     

氖中强冲击波结构及亮度温度

通过一维辐射流体动力学数值模拟，研究了氖中强冲击波的辐射特性、波阵面亮度温度及辐射场谱分布。模型考虑了一维不定常流体动力学方程与辐射输运方程的耦合，计算结果与实验数据符合良好。当冲击波速度大于３０ｋｍ／ｓ时，波阵面之前形成了加热层。加热层对于辐射的屏蔽作用是从长波部分开始的。当冲击波速度小于５０ｋｍ／ｓ时，对于可见光及紫外光的屏蔽作用不明显。但当冲击波速度大于５０ｋｍ／ｓ时，加热层对可见光已有了屏蔽作用，使亮度温度降低。     

比色测温技术在瞬态爆炸温度场测量中的应用研究

为了研究瞬态爆炸温度场分布规律,基于高速相机、黑体辐射理论、图像传感器的拜尔阵列和自编python代码,构建了依据比色测温原理的高速二维温度测试系统,并对添加不同含量TiH₂的乳化炸药、TiH₂粉尘以及C₂H₂气体的爆炸温度场进行了测量。实验结果表明:TiH₂的加入可以显著提高炸药的爆炸温度和火球持续时间,当乳化炸药中的TiH₂质量分数为6%时,爆炸平均温度最大值为3048 K,相比纯乳化炸药提高了41.5%;此外,TiH₂粉尘云火焰平均温度呈现先增大,再稳定,最后减小的趋势,浓度为500 g/m3的粉尘云火焰平均温度高于浓度为833 g/m3的平均温度,其最高平均温度分别为2231 和 2192 K;10%C₂H₂/90%空气预混气体（即体积分数为10%的C₂H₂和90%空气组成）的早期火焰温度均匀,内部略低于边缘温度,随着火焰膨胀,火焰边缘温度逐渐升高,火焰平均温度开始降低。与传统爆炸测温手段相比,比色测温方法可以准确测量某区域的瞬态爆炸温度,获得温度分布云图,为研究瞬态爆轰温度规律及影响因素提供了一种新的技术手段。     

壁湍流温度扩展的自相似性及其层次结构模型

用热线风速仪测量了风洞中壁面加热平板湍流边界层不同法向位置的温度信号,研究了温度结构函数扩展的自相似性及其层次结构模型与湍流平均流场的非均匀性的关系。     

用于测量材料高温动态力学性能的SHPB技术

讨论了高温下分离式Hopkinson压杆(SHPB)实验的两种方案:单独加热试样并快速对杆与同时加热试样和杆再修正温度梯度的影响。前者避免了杆被加热但是操作复杂,后者简单稳定。为了分析后者温度梯度的影响设计了一个简化模型,采用数值计算进行修正,提出了精度适当的假设,并且进行了实验验证。测量了试件和杆一起加热时杆上的温度分布,证实计算采用的温度分布是合理的。据此得到的专用于材料高温动态力学性能测试的SHPB数据处理公式简单实用,便于推广使用。     

具有规则表面织构的超高分子量聚乙烯髋臼表面温度分析

就人工关节中广泛使用的超高分子量聚乙烯(UHMWPE)髋臼在运行中的瞬态表面温度场进行了理论计算,与理想光滑表面对比考察了微球表面织构对接触压力分布的影响及其引起的表面温度变化.结果表明,基于光滑表面计算得到的髋臼表面温度偏低,而基于规则织构表面计算得到的温度与文献值接近;髋臼表面温度随摩擦系数和载荷增加而升高,随关节摆动而呈现周期性变化.     

块状金属样品冲击温度的辐射法测量——以铜为例

利用“三层介质模型”对不同冲击压力及卸载压力和不同初始间隙宽度下无氧铜／氟化锂界面温度进行模拟计算。结果表明．在所选的计算条件下．当初始间隙宽度lo=1μm时，非理想界面的表观界面温度和理想界面条件下的界面温度差异一般不超过3％．这已在辐射法测温的误差范围之内。根据“三层介质模型”，采用无氧铜块状样品进行冲击温度的辐射法测量，测量结果与理论计算一致。研究表明．基于“三层介质模型”，采用块状无氧铜样品与氟化锂窗口直接整合接触的方法来测量铜的冲击温度的方法是可行的。     

Theoretical analysis for the transient behaviour of radiative cooling of cavities in superconducting LINAC cryomodule

For the superconducting linear accelerator program, three cryomodules each houses eight superconducting cavities were successfully developed at IUAC, New Delhi. In each cryomodule, the cold mass at 4.2 K is surrounded by the liquid nitrogen cooled thermal shield maintained at 100 K. Three stages of cooling namely, radiation cooling followed by liquid nitrogen pre-cooling and finally liquid helium (LHe) cooling, are followed to reduce the temperature of cold mass from 300 to 4.2 K. The cold mass at 4.2 K consists of cavities, LHe vessel and the support structure. The temperature of cavity and helium vessel reaches to 210–220 K in 40 h of time by the natural radiation from the thermal shield. The radiative cooling rates for the cavities, helium vessel and support structure are found to be 3.0, 4.0 and 2.0 K/h respectively. A detailed analytical calculation has been done to understand the transient cool-down phenomenon for each component and compared with the experimental measured values. The experimental values are in agreement with the analytical data within 5 % variation considering the correction factor of radiation funneling. This paper presents the role of different thermal parameters like shield temperature, conduction load and radiation funneling area in the transient radiative cool-down behaviour of different components.     

Ideal gas interaction with thermal radiation in classical thermodynamics and Gibb’s paradox

The standard theory of ideal gases ignores the interaction of the gas particles with the thermal radiation (photon gas) that fills the otherwise vacuum space between them. Although acceptable in most cases, this feature of the theory contrasts with the evidence that all real materials, and hence in particular the particles of a real gas, absorb and radiate thermal energy. The interaction with the thermal radiation contained in the volume of a body may be important in gases. The latter, unlike solids and liquids, are capable of undergoing conspicuous volume changes, which entails large variations in the total amount of radiation that fills their volume in thermal equilibrium conditions. The paper considers a nonstandard ideal gas that differs from the classical one because it interacts with thermal radiation. This interaction is shown to produce temperature changes both in the free expansion of the gas and in its adiabatic mixing with another gas. Taking this kind of interaction into account also avoids the well-known Gibbs’ paradox still keeping the theory within the realm of classical macroscopic thermodynamics, i.e. without resorting to the current statistical mechanics explanation.     

颤振环境MoS2/Ag薄膜碰撞滑动接触摩擦性能研究

基于空间机构的运动特性,考虑空间颤振环境的影响,采用粗粒化分子动力学研究MoS₂/Ag薄膜的碰撞滑动接触摩擦性能,建立颤振环境碰撞滑动接触摩擦的粗粒化分子动力学模型,对比了纯Ag和MoS₂/Ag薄膜的摩擦性能,研究了初始碰撞速度、滑动速度以及空间温度对碰撞滑动接触摩擦过程的影响. 结果表明:与纯Ag相比,MoS₂/Ag薄膜表现出更优异的摩擦性能;压头碰撞速度对动能有一定的贡献,初始碰撞速度的增加会增大压头压入基体的深度,使得平均摩擦力增大;滑动速度的增加会加剧原子间的相互剪切摩擦,使平均摩擦力增加;MoS₂/Ag薄膜在100~500 K温度范围内表现出良好的摩擦性能,当空间温度为600 K时,其摩擦性能降低,并伴随着MoS₂膜的破裂.      

An oven design for torsional rheometers

A newly designed oven for rheological characterisation of polymer melts is presented which relies upon conduction and radiation rather than convection to heat the polymer. The design involves three concentric heating elements, all controlled independently to ensure a stable thermal atmosphere. The overshoot on heating is minimal (10 K, and this was due to opening the oven for sample trimming; the overshoot is 3 K if the oven is not opened) and the results of a typical dynamic shear test show that rheological properties attain their equilibrium values very rapidly (25 min after start-up of the oven fro room temperature, and 15 min after the sample was placed in the rheometer). The temperature of the sample was maintained at ±0.5 K, thus, a stable thermal environment was successfully attained.     

Radiational properties of the decomposition products of a model around which flows a subsonic high-temperature plasma stream

Models made of an asbestos plastic were tested in a subsonic jet of air heated to T = 8500 °K with p = 1 atm. The multicomponent thermal boundary layer arising at the decomposing surface of the model has a complex structure. At the surface of the model, in the critical region of the boundary layer, there is a sublayer with an extension of 1.5-2 mm where the temperature of the gas is constant and its composition is unchanged to a great degree and is mainly determined by the decomposition products of the asbestos plastic. In this region the spectral distribution of the intensity of the radiation of the vapors of the asbestos plastic was obtained in a range of 0.3-0.9, which makes it possible to calculate the spectral coefficients of absorption for a temperature of 3500 °K. The radiating power of the vapors is compared with the radiation of an air plasma of the oncoming flow.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 76– 80, November–December 1978.The authors are indebted to Yu. K. Rulev for his aid in carrying out the experiment.     

Spectroscopic research on infrared emittance of coal ash deposits

This paper deals with thermal radiation characteristics of ash deposits on a pulverized coal combustion boiler of an electric power plant. Normal emittance spectra in the near to medium infrared (2.5–25 μm) region and total normal emittances were measured on four kinds of ground ash deposits. Measurements were conducted in the 570–1460 K temperature range which is common for boiler furnaces, by both heating and cooling the ash samples, with the aim to study the effect of their thermal history. Dependence of emittance on wavelength, temperature and chemical composition was studied, too. Samples were tested for transparency (opacity) to verify the accuracy of results. It was determined that the thicknesses used for the ash powders are opaque for infrared radiation for thicknesses in the order of a millimeter. Tests have shown that spectral emittance increases with an increase of wavelength with a characteristic pattern common for all samples. Spectral normal emittance increases strongly with temperature at shorter wavelengths and remains high and unchanged at longer ones. Emittance spectra are not very sensitive to chemical composition of ashes especially beyond λ ≈ 5 μm. With an increase of temperature, total emittance of the powdered sample decreases to a minimum value around 1200 K. Further temperature rise induces an increase of total emittance due to sintering in the ash. On cooling, the emittance increases monotonically following the hysteresis. Quantitative directions for evaluating thermal radiation characteristics of ash deposits for the merits of the safety design of boiler furnaces were proposed. That comprises correlating the experimentally obtained emittance spectra with curves of simple analytical form, i.e., a continuous function of minimum emittance vs. wavelength. The proposed method can be extended to other specimens from the same furnace and used to determine correlations for thermal calculation of old and design of new furnaces – with similar geometry and combusting similar coal. The method is potentially applicable to completely different boiler furnaces combusting different coal, and the authors recommend running the tests with new deposit samples. The data will then be applicable to the thermal design of a whole new class of furnaces, having similar geometry and combusting similar coal. This is expected to greatly enhance the accuracy and precision of thermal calculation as well as the efficiency of thermal design of steam boilers.     

结构层热扩散系数对超薄涂层热力性能的影响

将非傅立叶热传导模型(用于超薄热涂层)与傅立叶热传导模型(用于结构层)相结合 求解温度场，运用有限元法求解热涂层热应力和裂纹驱动力，并分析结构层材料热扩散系数 的变化对热涂层的热力学性能(温度场、应力场和断裂性能)的影响. 研究表明，结构层材 料性能变化对温度场的影响主要表现在热冲击后期，对热应力和裂纹尖端驱动力后期的变化 也有一定的影响.     

Effects of partial slip on boundary layer flow past a permeable exponential stretching sheet in presence of thermal radiation

An analysis is presented to describe the boundary layer flow and heat transfer towards a porous exponential stretching sheet. Velocity and thermal slips are considered instead of no-slip conditions at the boundary. Thermal radiation term is incorporated in the temperature equation. Similarity transformations are used to convert the partial differential equations corresponding to the momentum and heat equations into highly non-linear ordinary differential equations. Numerical solutions of these equations are obtained by shooting method. It is found that the fluid velocity and temperature decrease with increasing slip parameter. Temperature is found to decrease with an increase of thermal slip parameter. Thermal radiation enhances the effective thermal diffusivity and the temperature rises.     

A mechanistic IR calibration technique for boiling heat transfer investigations

This paper presents a new calibration technique to improve the accuracy of infrared thermometry in boiling heat transfer investigations.The technique is suitable for heaters consisting of a thin, infrared (IR) opaque conductive film coated on one side of a flat and IR semi-transparent substrate. The conductive film is in contact with the liquid and acts as the boiling surface. The IR camera sees the boiling surface through the substrate. If the substrate is not completely transparent, the radiation emitted by the IR opaque film is partially absorbed and contaminated by the radiation emitted by the substrate itself. Therefore, the correlation between the IR radiation measured by the IR camera and the temperature of the boiling surface (IR opaque film) is not unique, but depends on the temperature distribution in the substrate.To solve this issue, we developed a model that solves the coupled conduction/radiation inverse problem in the heater. The problem is inverse because the boundary condition for the conduction problem (the boiling surface temperature) is not known. The IR camera measures the combined radiation emitted by the boiling surface, emitted by the substrate and also the reflection of the background radiation; from that information one has to reconstruct the boiling surface temperature.The technique is unique in that it takes into account the spectral dependence of optical properties in the optical materials. For this reason, it is particularly suitable for heaters where the optical properties of the conductive film and the substrate materials depend on the wavelength of the IR radiation.Using this technique, we can measure with improved accuracy the time-dependent 3D temperature distribution in the heater, as well as local temperature and local heat flux distributions on the boiling surface. The validation of the technique was carried out using transient conduction experiments. Then, the technique was applied to transient pool boiling experiments to prove its feasibility and show the potential applications.