考虑人体散热的轿车座舱内流场数值仿真研究

研究提高轿车热舒适性,汽车座舱空气的对流和人员体温,都会影响舒适度,有必要在开发前期,用数值方法对轿车座舱内流场进行仿真.根据雷诺平均的方法,应用RNGc-E湍流模型,为了控制舱内舒适性能,采用分区域划分网格的方法,对座舱内空气三维流场和温度场进行了数值仿真研究.引入人体模型,考虑车内人体散热对座舱内环境的影响,建立了轿车座舱舒适性研究的模型.给出了座舱内不同位置的速度分布和温度云图,分析了空调给风角度、空调给风口位置以及空调回风口位置对座舱内气流组织及温度场的影响.结果表明,采用前-中给风的给风口布置和后回风形式以及上攻角的给风口设计,均可以提高轿车座舱内乘员的热舒适性.     

飞机防滑刹车系统副温度场研究

在飞机制动系统刹车副温度场优化问题的研究中,由于飞机制动过程摩擦产生的高温可严重影响刹车副的热机械性能,出现热衰退现象,影响飞机着陆安全,但又无法通过测量得到温度场分布.为解决上述问题,提出建立综合多方面因素的刹车副温度场计算模型.建立了具有热辐射边界条件飞机刹车副温度场计算的有限元模型,考虑了飞机制动过程中热生成率的...     

飞机刹车盘温度场的有限元分析

飞机的刹车装置是利用摩擦产生制动将高速运动的动能转换成热能,产生的高温使摩擦材料的物理、化学性质变化,刹车装置系统的安全性能因此得不到保证,所以对刹车盘瞬态温度场进行计算就非常有必要.针对飞机刹车盘瞬态温度场仿真建立了有限元计算模型,运用迦辽金法推导了各单元方程,在单元内部采用一次函数来近似刹车盘的温度值.有限元网格划分采用四面体结构.重点研究刹车过程的理论分析与计算,并用ANSYS对其进行了仿真计算.仿真计算结果与刹车盘实际温度场基本吻合,所建立的有限元计算模型是合理可行的,可以应用于飞机刹车盘设计过程中的温度场计算.     

整流器件热分析及其风冷散热器的仿真研究

研究整流器优化散热结构设计问题,对电力变换装置小型化和高功率密度要求越来越严格,功率器件散热技术研究和分析变得尤为重要,针对散热器结构散热性差,影响工作的稳定性.为了能够直观和准确地获得散热器温度场的分布特性,根据传热理论建立了整流器件散热的物理模型,采用了热分析方法(有限元法),应用ANSYS软件对风冷散热器温度场进行了数值计算.计算中考虑了整流器件在风冷散热器上的整体布局,着重对两种肋片形状的风冷散热器进行了仿真,结果对比两种风冷散热器的传热效果.给出了风冷散热器优化设计后的实际结构,为散热优化提供了参考.     

粗糙表面Cantor集分形对温度场影响分析

由于Cantor集性质较好,能够很好地模拟粗糙表面,已应用到温度场研究中,但其参数的取得以及微凸体排列对温度场的影响尚未有公开的研究和应用。进行Cantor集粗糙表面参数估计,在样本足够大时,模型可以以任意精度收敛于实际参数。考虑排列不唯一时微凸体之间不同的组合,以飞机刹车副C/C材料为例对其进行计算和仿真分析而后推广,从仿真结果可以看出Cantor集的排列对温度场的影响,应该按照工程实际进行处理,为深入研究各种温度场分布以及各种粗糙表面的热物理效应打下基础。     

A型地铁空调系统及客室内流场数值分析

为给目前国内A型地铁车辆的舒适度设计提供理论参考,针对地铁车辆静压风道结构特点,基于k-ε两方程湍流模型和SIMPLE算法,建立包含空调送风风道和客室的三维计算模型.对计算模型的空气流动和传热状况进行CFD数值计算.计算过程综合考虑车体壁面传热和人体散热等多种传热.分析计算结果得到客室内温度场和速度场的分布规律,并对空调通风设计方案进行量化评估.计算结果表明:客室内人体头部区域温度场分布均匀,平均温度为26.6℃,最大温差为6℃;车厢内有较理想的气流组织形式,速度分布范围为0.50~0.79 m/s,而且客室端部和中部区域人体头部周围速度较大.将计算结果与欧洲EN 14750-1标准进行对比分析,认为乘客的舒适性较好.     

汽车乘员舱空调制冷CFD瞬态分析

为提高汽车乘员舱的热舒适性,缩短空调制冷系统的开发周期,降低开发成本,对某车型乘员舱空调制冷过程进行30 min的CFD瞬态计算.由管道流量分配和总压分布可知,各管道流量分配较均匀,总压分布合理,没有压力损失过大的区域.由气流速度分布和温度场随时间变化情况可知,空调开启15 min后乘员舱温度基本稳定不变,达到人体舒适温度,但舱内后排中间位置温度偏低.计算得到的舱内监控点温度曲线与试验所测温度曲线基本吻合,证明该数值仿真方案有效.     

飞机刹车盘三维瞬态温度场仿真

针对单一工况的飞机刹车盘三维瞬态温度场仿真不能全面描述温度场在其他工况下的热特性。为获取多工况的刹车盘制动过程中的温度分布情况,以某型飞机为例,对刹车装置的循环对称结构,根据传热学理论建立三维循环对称有限元模型,阐述飞机刹车副制动过程中三维瞬态温度场的计算方法,运用ANSYS10.0软件分析不同工况下刹车盘的温度分布,并给出典型时刻下温度场分布云图和最高温度点温度变化曲线。通过分析不同制动过程的温度场,为摩擦材料的研制及制动盘的设计和选择不同工况的压力和制动速度提供有效的参考。     

柴油机缸盖有限元分析

用Abaqus将对流热边界耦合至固体传热计算中,得到柴油机缸盖的温度场.在此基础上进行预紧力和爆发压力-热应力2种工况的数值仿真.仿真结果可以帮助确定各影响因素造成的缸盖应力集中的主要位置,为结构设计和改进提供参考.     

滚动轮胎有限元建模及温度场仿真分析

研究滚动轮胎温度场分布的问题,为了解决温度场试验较难获得轮胎内部温度,重复性差等缺点,以实体轮胎为建模对象,建立了胎体帘线模型与轮胎橡胶材料模型,并将模型在充气压力下的自由模态各阶频率值与试验值相比较,在验证了可行性和正确性的条件下,嵌入了轮胎生热、传热模型以及试验测得的热边界条件,对轮胎稳态温度场进行了仿真,明确了稳态温度场分布图和轮胎内部最高温度与车速间的函数关系及二次拟合公式,并简单分析了轮胎温度分布规律.仿真结果表明,利用有限元法建立的模型及温度场计算是正确的,可为轮胎的结构和配方设计等方面提供了依据.     

A two-dimensional study on natural convection and heat transfer in the enclosure with heat transfer and radiation coupled in natural convection

Numerical investigation using SIMPLE algorithm with QUICK scheme for natural convection and heat transfer in the enclosure bounded by a solid wall and with heat transfer and radiation coupled in natural convection has been conducted.The various parameters are:Rayleigh number(from 103 to 105),dimensionless conductivity of bounding wall(from 0 to 100),dimensionless wall thickness(from 0 to 0.6) and radiation emissivity of all surfaces(from 0 to 1).The results suggest that flow and heat transfer are influenced...     

Enhancement of heat transfer in a convergent/divergent channel by using carbon nanotubes in the presence of a Darcy–Forchheimer medium

This article explores the influence of thermal radiation on the flow and heat transfer of single-walled carbon nanotubes over both a convergent and divergent channel. Flow is induced due to a Darcy–Forchheimer medium. Further, the heat transfer mechanism is analyzed in the presence of a thermal radiation process. Guided by some appropriate similarity transformations, the fundamental PDEs are converted into a self-similar system of coupled non-linear ODEs. The findings are obtained with the help of the Runge–Kutta-45-based shooting method. The roles of the Reynolds number, porosity parameter, inertia coefficient parameter, Prandtl number and radiation parameter are presented graphically. Results are displayed and show that the rate of heat transfer is higher in a divergent channel as compared to a convergent channel.

     

Size effect on heat transfer in micro gas sensors

Gas gap is usually used as an important thermal insulation in micro gas sensors to reduce the heating power. The heat transport through the gap consists of two parts, heat conduction by air and thermal radiation between surfaces. It is usually regarded that thermal radiation through the gap is negligible compared with conductive heat transfer by air. This work investigates the heat transport by thermal radiation and heat conduction through a broad size range of gas gaps from one nanometer to dozens of micrometers. The result shows that thermal radiation is the major way of heat transfer when the gap is less than 20 nm, which will result in unexpected high energy consumption in the process of minimization. The equivalent thermal conductivity of thermal radiation is computed and a partition map is depicted to demonstrate the relative importance of radiation and conduction on different gap scales under dissimilar surface temperatures. A practical gas sensor heated by a micro hotplate (MHP) is thermally analyzed. The calculation shows that extra energy consumption comes forth as the gap distance reduces to several tens of nanometers.     

一种新型MEMS器件中的近场辐射传热现象研究

以近场辐射传热方式利用光电器件中的热能制作热光电器件从而提高整个器件转换效率的思想已经被提出。本文基于该思想设计一种新型的具有双悬空薄膜的器件,两个薄膜面对面相互平行,间距为1 ?m。每个悬空薄膜中制作白金薄膜电阻。这个器件利用MEMS工艺中的牺牲层技术制作。在存在近场辐射传热和不存在近场辐射传热两种情况下,通过测量将下方结构加热到相同温度的输入功率差,测量出两个薄膜间的辐射热功率。实验数据表明该器件中薄膜间的传热已经大于黑体辐射传热;并且,当上方薄膜温度为317.2 K时,通过近场辐射传热可以使下方薄膜的温度从293 K升高294.2 K,该温度变化为热电转换提供了条件。     

机载雷达告警系统中威胁等级判定方法研究

在机载雷达告警系统中,辐射源威胁等级判定对自动实施有效的干扰功率分配和提高作战飞机的生存能力至关重要。针对现在作战飞机所面临的多目标作战情况,利用模糊数学建立了威胁指标的隶属度模型,通过层次分析法和熵值法获得了各威胁指标的主观和客观权重,用综合赋权法融合了主客观权重,最后根据机载雷达告警系统的综合性能要求,建立了辐射源威胁等级判定函数,实现了对辐射源威胁等级的判定。通过实例应用说明了该方法能够有效地判定辐射源的威胁等级。     

高温条件下材料表面电阻率测试方法研究

飞行器在空中飞行时因为各种原因产生的静电放电可能导致其油箱的起火爆炸,静电放电产生的辐射还会对飞行器的通讯和导航系统造成干扰,这就需要飞行器的表面材料具有一定的防静电性能。表面电阻率是衡量材料防静电性能的一个重要参数,飞行器在空中高速运动过程中会因与大气摩擦而产生很高的热量,因此,测量高温条件下材料的表面电阻率尤为重要。对于常温态下材料的表面电阻率的测试有三电极法、两电极法等测试方法。本文通过对比分析三电极法和两电极法,在两电极法的基础上提出了高温条件下表面材料电阻测试方法,并构建了高温条件下材料表面电阻率测试系统。通过对某材料随温度升高的表面电阻率的测试,证明该方法的可行性。     

Transfer of radiative heat through clothing ensembles

A mathematical model was designed to calculate the temperature and dry heat transfer in the various layers of a clothing ensemble, and the total heat loss of a human who is irradiated for a certain fraction of his or her area. The clothing ensemble that is irradiated by an external heat source is considered to be composed of underclothing, trapped air, and outer fabric. The model was experimentally tested with heat balance methods, using subjects, varying the activity, wind, and radiation characteristics of the outer garment of two-layer ensembles. In two experiments the subjects could only give off dry heat because they were wrapped in plastic foil. The model appeared to be correct within about l°C (rms error) and l0Wm^?2 (rms error). In a third experiment, sweat evaporation was also taken into account, showing that the resulting physiological heat load of 10 to 30% of the intercepted additional radiation is compensated by additional sweating. The resulting heat strain was rather mild. It is concluded that the mathematical model is a valid tool for the investigation of heat transfer through two-layer ensembles in radiant environments.     

Visual simulation of heat shimmering and mirage

We provide a physically-based framework for simulating the natural phenomena related to heat interaction between objects and the surrounding air. We introduce a heat transfer model between the heat source objects and the ambient flow environment, which includes conduction, convection, and radiation. The heat distribution of the objects is represented by a novel temperature texture. We simulate the thermal flow dynamics that models the air flow interacting with the heat by a hybrid thermal lattice Boltzmann model (HTLBM). The computational approach couples a multiple-relaxation-time LBM (MRTLBM) with a finite difference discretization of a standard advection-diffusion equation for temperature. In heat shimmering and mirage, the changes in the index of refraction of the surrounding air are attributed to temperature variation. A nonlinear ray tracing method is used for rendering. Interactive performance is achieved by accelerating the computation of both the MRTLBM and the heat transfer, as well as the rendering on contemporary graphics hardware (GPU)     

虚拟冠层光辐射传输仿真系统设计

研究光在虚拟植被冠层中的辐射传输特性,是虚拟植物研究的一个难点和关键点.为了利用计算机仿真虚拟冠层中的光辐射传输过程,面向对象技术设计了一个虚拟冠层光辐射传输仿真系统(VPCRTS),采用基于混合式八叉树空间剖分技术的蒙特卡罗光线跟踪算法对光在植被冠层内的辐射传输过程进行了仿真.VPCWTS以一种可视化的直观方式展现了整个辐射传输过程,可以针对冠层的不同散射模型进行仿真和对比.VPCRTS系统仿真的结果具有一定的物理可靠性,为研究光在植被冠层中的辐射传输特性提供了一有效的工具.