Prediction of hypersonic boundary layer transition on sharp wedge flow considering variable specific heat

When the air temperature reaches 600 K or higher, vibration is excited. The specific heat is not a constant but a function of temperature. Under this condition, the transition position of hypersonic sharp wedge boundary layer is predicted by using the improved eN method considering variable specific heat. The transition positions with different Mach numbers of oncoming flow, half wedge angles, and wall conditions are computed condition, the nearer to the Mach number The results show that for the same oncoming flow condition and wall transition positions of hypersonic sharp wedge boundary layer move much leading edge than those of the flat plate. The greater the oncoming flow the closer the transition position to the leading edge.

Floating zone growth and magnetic and specific heat properties of La0.67Ca0.33Mn1-xFexO3（x=0.00,0.04）single crystals

Single crystals of La0.67Ca0.33MnO3 and La0.67Ca0.33Mn0.96Fe0.04O3 were obtained by floating zone method. Laue diffraction pattern and rocking curve of the single crystals show that their quality is good. The magnetic behaviours of these compounds have been studied. Fe doping significantly depresses the magnetic contribution to the total specific heat Cp, but slightly influences the lattice contribution at temperatures above 50K. The peak of Cp shifts towards high temperatures with increasing magnetic field. Both single crystals exhibit the first-order magnetic transition around the Curie temperature.

基于降低电流负载法的双馈风力发电机温升试验研究

本研究运用降低电流负载的方法对3.4 MW双馈型风力发电机进行了温升试验,结果表明降低电流负载法得到的电机温升值与全功率试验下的电机温升值吻合度较高,误差仅为1 K左右。该方法可在容量较小的试验站试验较大功率电机的情况下使用,对电机试验设备能力不足或不具备全功率试验条件的情况下做温升试验有重要实践指导意义。

Specific heat ratio effects of compressible Rayleigh—Taylor instability studied by discrete Boltzmann method

Rayleigh-Taylor(RT)instability widely exists in nature and engineering fields.How to better understand the physical mechanism of RT instability is of great theoretical significance and practical value.At present,abundant results of RT instability have been obtained by traditional macroscopic methods.However,research on the thermodynamic non-equilibrium(TNE)effects in the process of system evolution is relatively scarce.In this paper,the discrete Boltzmann method based on non-equilibrium statistical physics is utilized to study the effects of the specific heat ratio on compressible RT instability.The evolution process of the compressible RT system with different specific heat ratios can be analyzed by the temperature gradient and the proportion of the non-equilibrium region.Firstly,as a result of the competition between the macroscopic magnitude gradient and the non-equilibrium region,the average TNE intensity first increases and then reduces,and it increases with the specific heat ratio decreasing;the specific heat ratio has the same effect on the global strength of the viscous stress tensor.Secondly,the moment when the total temperature gradient in y direction deviates from the fixed value can be regarded as a physical criterion for judging the formation of the vortex structure.Thirdly,under the competition between the temperature gradients and the contact area of the two fluids,the average intensity of the non-equilibrium quantity related to the heat flux shows diversity,and the influence of the specific heat ratio is also quite remarkable.

An Improved Finite Temperature Lanczos Method and Its Application to the Spin-1/2 Heisenberg Model on the Kagome Lattice

We present an improvement of the finite temperature Lanczos method in order to apply this method to systems at very low temperature. One proposal is to introduce two steps in this method. In the first step, we use the Chebyshev polynomial expansion to calculate exp(-H/T1) random vector>?at moderate temperature T1. In the second step, we apply the ordinary finite temperature Lanczos method using the calculated state as the initial state of the Lanczos method. Another proposal is to employ a sampling method for selecting a random vector. By this sampling, we can improve an efficiency of calculations. Using the improved finite temperature Lanczos method, we calculate the specific heat of the spin-1/2 Heisenberg model on the kagome lattices of 27 and 30 sites.

Investigation of Thermodynamic Properties of Zirconia Thin Films by Statistical Moment Method

The moment method in statistical (SMM) dynamics is used to study the thermodynamic quantities of ZrO2 thin films taking into account the anharmonicity effects of the lattice vibrations. The average lattice constant, thermal expansion coefficient and specific heats at the constant volume of ZrO2 thin films are calculated as a function of temperature, pressure and thickness of thin film. SMM calculations are performed using the Buckingham potential for the ZrO2 thin films. In the present study, the influence of temperature, pressure and the size on the thermodynamic quantities of ZrO2 thin film have been studied using three different interatomic potentials. We discuss temperature and thickness dependences of some thermodynamic quantities of ZrO2 thin films and we compare our calculated results with those of the experimental results.

应用功率补偿型微量热仪测定磷酸脲的比热容

采用功率补偿型微量热仪连续测量样品在精准控制的升降温过程中的微小能量变化,从而得到准确的比热容数据。对水、蓝宝石、苯甲酸等6种物质(4种固体、2种液体)比热容的测定结果与文献值的偏差在1.2%以内,表明该方法具有较高的测量精度,适用于各种固体和液体比热容的连续测量。以磷酸和尿素为原料,通过络合反应、冷却结晶制备得到了磷酸脲晶体产品。元素组成分析、XRD、红外光谱和熔点测试结果表明,所制备的磷酸脲具有很高的纯度和结晶度。进一步,采用该方法测量了磷酸脲在-20~100℃范围内的比热容,并对测试数据进行了关联和相关热力学函数计算。本工作为磷酸脲在食品加工领域的应用提供了重要数据,也为各类食品添加剂比热容提供了一种新的高效测定方法。

反求铝合金淬火边界条件的序列LM梯度算法

准确获取边界条件在淬火仿真中至关重要。为此,根据瞬态热传导模型,利用正则化方法建立反求热通量的目标函数,结合序列函数指定法与LM梯度法,通过最小化目标函数推导出序列LM梯度算法,实现末端淬火实验中热通量的迭代计算。其次,通过训练观测点的平均绝对误差的“3-7-3”神经网络预测模型,建立了序列LM梯度算法关键参数的遗传算法优化方法。最后,以换热系数为边界条件建立淬火仿真模型。结果表明:在相同淬火时间内,一维序列LM梯度算法、一点法和两点法,在观测点的仿真温度平均相对误差分别为5.6%、5.9%、12.6%,17.1%、15.4%、15.3%和17.7%、16.0%、15.6%。因此,与一点法、两点法相比,序列LM梯度算法具有更高的精度。

Nb元素含量对U-Nb合金显微组织和比热容的影响

U-Nb合金具有良好的耐腐蚀性、结构稳定性和加工性,是核领域重要的结构材料。制备了不同Nb元素含量的淬火态U-Nb合金,对其显微组织和比热容进行了研究。结果表明:淬火态U-2Nb合金中存在大量粗针状马氏体;随着Nb元素含量的增加,马氏体逐渐消失,U-Nb合金形成等轴晶组织;随着Nb元素含量增加和温度的升高,U-Nb合金的比热容逐渐增大;当温度超过650℃时,U-Nb合金发生了相变,比热容显著减小。

Prediction of hypersonic boundary layer transition with variable specific heat on plane flow

When an aircraft flies at a hypersonic speed,the temperature of gas inner boundary layer near the wall is so high that the specific heat is no longer a constant but dependent upon the temperature.It is necessary to consider its effect on transition location.In this paper,the transition locations of hypersonic plane boundary layer are predicted with the improved e N method,and the results of the specific heat dependent upon temperature are compared with those of constant specific heat.The flow parameters are taken as those corresponding to the condition at a height of 40 km and the Mach numbers of oncoming flow are 6,7,and 8,respectively.It is found that the transition locations calculated by the variable specific heat are closer to the leading edge than those by the constant specific heat.The deviations in most cases are around 30 percent.All the results prove that the real gas effect should be taken into consideration when one predicts transition location for hypersonic flow.Whether the first or second mode wave determines the transition location relies on the oncoming flow Mach number and the wall condition.

基于三维特征线法的尾喷管设计方法研究

提出了一种基于三维特征线法的单边膨胀喷管型面生成方法,以进一步提升高超声速喷管的气动性能。采用三维数值模拟方法,对比分析了基于三维和二维特征线法设计的三维单边膨胀喷管的特性,观察到两者型面的差异主要体现在周向壁面,在典型的飞行工况下,基于三维特征线法设计的喷管气动性能更优,其中轴向推力系数均提升0.45%以上,升力系数均提升8%以上。进一步考虑变比热的影响,完成了变比热三维单边膨胀喷管设计,与定比热三维单边膨胀喷管进行了对比分析,两种喷管型面差异明显,变比热三维单边膨胀喷管的面积比明显减小,气动性能显著提升,尤其升力系数在典型的飞行工况下增幅均超过50%。

响应面法优化消防水带热泵微波联合干燥工艺

为解决利用热泵对消防水带干燥时后期干燥速率慢、能耗高的问题,提出采用热泵+微波联合干燥的方式。设计和搭建热泵微波联合干燥实验台,设计分别以热泵初始送风温度、热泵干燥时间以及微波功率为自变量的单因素实验,以此确定各因素的影响范围,在单因素实验基础上以SMER、MER、ηen为指标,采用Box-Behnken中心组合实验设计并进行响应面优化分析。结果表明,热泵微波联合干燥消防水带优化工艺参数为:初始送风温度42.3℃、热泵干燥时间43.45 min、微波功率1.25 kW。在此条件下得到SMER为0.658 kg/kWh,MER为1.232 kg/h,微波能量利用率为63.7%。实验验证结果与模型预测值相近,相对误差均小于4%,表明优化结果可靠。

基于LSSVM函数的两相流含油率测量仿真研究

两相流体间存在较强的相互作用,界面扰动较大,易产生异常数据点,影响数据采集,导致难以精准反映油体比热特征,使得含油率测量误差较大。因此,展开基于支持向量机的两相流含油率测量方法仿真研究。在已知两相流系统含油率条件下采集传感数据,并在3σ准则的基础上引入奇异谱分析法,以剔除因干扰所产生的异常数据点,获得有效数据。依此计算油体比热值,来反映油体比热特征。结合最小二乘法与支持向量机算法构建LSSVM函数,通过多次训练与学习,提升LSSVM函数的泛化能力,确保测量准确性。依此将获得的油体比热值作为输入,利用训练后的LSSVM函数实现含油率测量。实验表明,采用所提方法测量后,NSE最高可达到0.98,表明其能够实现两相流含油率的精准测量。

大学物理实验中两种空气比热容比测量方法的比较

实验是科学素养培养的重要组成部分,一些地方院校在培养物理师范生的过程中会有意培养大学生的科学素养与实验探究能力。其中开展大学物理实验是科学素养培养的重要环节。大学物理实验的力热实验往往会开设空气比热容比的测量实验。在利用HZDH声速测定信号源和SV-DH-7型声速测定仪测定声速实验的基础上,将通过声速公式推导出的空气比热容比作为理论基础,并以此原理实现空气比热容比的测定(声速测定法),与利用传统DH4602气体比热容测定仪(振动法)实现空气比热容比的测定的实验结果进行对比。将两种方法的操作步骤以及测得的结果进行对比,最后得出,声速测定法测得的空气比热容比的实验数据误差远较于DH4602空气比热容比测定仪的实验数据误差更大,即DH4602气体比热容具有更高的精度。

闪光法测量C/C复合材料导热系数影响因素研究

C/C复合材料已在航空航天领域及原子能领域得到了广泛的应用,其工作温度可达1000℃以上。为对C/C复合材料导热系数进行测定,使用闪光法测定了C/C复合材料25℃至1000℃的热扩散系数和比热容,并对石墨喷敷、样品厚度、参比样品和修正模型的影响进行了研究。研究结果表明,为提高C/C复合材料热扩散系数测试准确度,样品应不喷敷石墨,测试结果使用渗射模型修正;为提高C/C复合材料比热容测试准确度,样品应均匀喷敷石墨,并使用石墨标准样品作为参比样品,测试结果使用Cowan模型修正。

橡胶和炭黑种类对硫化胶导热性能的影响

研究4种橡胶[天然橡胶(NR)、溶聚丁苯橡胶(SSBR)、乳聚丁苯橡胶(ESBR)、顺丁橡胶(BR)]配方和9种炭黑配方硫化胶的导热性能,建立硫化胶比热容的准确测试方法,分析得出导热性能相对优良的橡胶和炭黑种类。结果表明:调制差示扫描量热法(MDSC法)能够真实反映硫化胶的比热容,提高测试效率和准确度;不同橡胶和炭黑配方硫化胶的比热容均随温度的升高而增大,热扩散系数与温度有较好的线性负相关性,导热系数均随温度的升高呈现减小趋势;相同温度下,BR,ESBR,SSBR,NR硫化胶的热扩散系数和导热系数均依次减小;炭黑结构度高、粒径小有利于硫化胶热扩散系数的增大,中等粒径炭黑对于提高硫化胶的导热系数有较好的效果。

基于基团贡献法的生物柴油比定压热容的理论研究

生物柴油是一种可再生的清洁能源,主要原材料是植物油、废弃的餐饮油(地沟油)和动植物脂肪等,主要应用于表面活性剂、天然脂肪醇、工业溶剂、工业润滑剂、生物酯增塑剂、醇酸树脂等。比定压热容是流体的热工性能关键参数,是计算热工设备中工质焓变的基础数据,同时也是流体流动和传热计算的必要数据。采用基团贡献法研究在生物柴油中各基团随压力及温度的变化规律,提出了生物柴油主要组分脂肪酸酯类物质的比定压热容计算模型。与实验数据相比,模型计算值的最大偏差为2.7%,绝对平均偏差为0.79%,具有较高的计算精度,适用于温度333~433 K,及压力0.1~10 MPa范围内脂肪酸酯类物质的比定压热容计算。该模型的提出能够为生物柴油的推广应用提供基础热物性数据。

凝固过程数值模拟中的潜热处理方法

本文介绍了凝固过程数值模拟中潜热处理的几种方法 ,简单比较了它们的优缺点。提出了把等价比热容法应用到纯金属、共晶合金以及窄凝固区间合金的潜热处理上的观点 ,并完善了其温度校正方法。

快速冷却条件下凝固潜热处理模型的研究

深入分析了有限差分法模拟凝固过程时,采用等效比热法处理相变潜热的原理;从理论和实际计算角度分析了快速冷却条件下常规的等效比热法会造成热量"虚增",模拟计算结果失真的原因和影响程度;并进一步建立了快速冷却条件下凝固潜热处理的模型。计算结果表明,该模型可以充分保证模拟计算的精度和效率。

铸件凝固潜热的处理方法与应用研究

通过温度回升法与等效热容法的结合,提出了一种能够处理铸件凝固潜热释放问题的方法,它可适用于任意结晶温度区间,且计算效率很高。以生产厂铸件为研究对象,将此处理方法应用于预测铸件凝固时的温度分布,结果表明,计算值与实测值相符。