共查询到19条相似文献,搜索用时 984 毫秒
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通过在格子Boltzmann (LBM)热模型中添加参数项,使得在对应的宏观传热方程中,消除了一阶非线性误差项,具备二阶精度.通过Rayleigh-Benard对流数值试算,初步探索该二阶精度格式及其对应的一阶精度格式三个热模型的传热特征和适应性,并做出相应对比分析.针对一二阶精度模型在Ra数极高或热传导系数极大时,Nu数的计算与经验值相比出现较大偏差,分析LBM对应宏观热传导方程的截断误差后,在平衡分布函数中引进一个调节因子.通过调节对应宏观传热方程的截断误差项系数,校正Nu数的计算偏差,提高模拟精度,拓展模拟范围,增强了LBM作为一个数值方法在传热中的适应性. 相似文献
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隐式格式求解拟压缩性非定常不可压Navier-Stokes方程 总被引:1,自引:0,他引:1
采用Rogers发展的双时间步拟压缩方法,数值求解不可压非定常问题.数值通量分别采用三阶精度Roe格式和二阶精度Harten-Yee的TVD格式离散.为了加快收敛,提高求解效率,试验了几种隐式格式(ADI-LU,LGS,LU-SGS).针对经典的低雷诺数(Re=200)圆柱绕流问题,比较了不同隐式方法的计算结果和求解效率,以及两种数值离散格式计算结果的异同.最后采用Roe格式数值求解了两种典型的低速非定常流动问题:绕转动圆柱(ω=1)低雷诺数流动;NACA0015翼型等速拉起数值模拟. 相似文献
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局部热壁面多孔介质方腔内自然对流的数值研究 总被引:1,自引:0,他引:1
本文对上下壁面绝热、左侧壁面长度为b的嵌装加热器部分维持恒定温度T_h而剩余部分绝热,且右侧壁面维持恒定温度T_c的多孔介质方腔内的自然对流换热进行了数值研究.在热壁面无量纲长度B=0.5(B=b/L)的条件下,综合研究了左侧壁面受热部分中心距上壁面的无量纲长度D(D=d/L)、Da数、Ra数和孔隙率对腔体内自然对流换热的影响.数值计算结果表明,左侧壁面受热部分位置的不同对腔体内自然对流换热有很大的影响,D在0.6附近取值时,Na数最大.Da数、Ra数对腔体的自然对流换热影响较大,而孔隙率对换热的影响较小. 相似文献
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针对二维非定常半线性扩散反应方程,空间导数项采用四阶紧致差分公式离散,时间导数项采用四阶向后Euler公式进行离散,提出一种无条件稳定的高精度五层全隐格式.格式截断误差为O(τ4+τ2h2+h4),即时间和空间均具有四阶精度.对于第一、二、三时间层采用Crank-Nicolson方法进行离散,并采用Richardson外推公式将启动层时间精度外推到四阶.建立适用于该格式的多重网格方法,加快在每个时间层上迭代求解代数方程组的收敛速度,提高计算效率.最后通过数值实验验证格式的精确性和稳定性以及多重网格方法的高效性. 相似文献
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本文发展了差分法求解流动与换热问题的三维非均分网格7点紧致格式,并利用延迟修正方法将其与SIMPLE算法相结合形成了一种三维紧致修正方法。利用所发展的紧致修正方法对圆筒内同心开缝圆筒的三维自然对流与换热问题进行了数值模拟,所获得的数值结果与实验结果一致。采用Richardson方法证实所发展的三维紧致修正方法大约具有4阶精度。进一步的数值计算表明,在特征参数Ra数大于一定值时,由圆筒内同心开缝圆筒的三维自然对流问题简化的二维模型数值结果与实验结果逐渐加大,用三维模型才能得到比较可靠的结果。 相似文献
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求解对流扩散方程的紧致修正方法 总被引:1,自引:0,他引:1
提出了求解对流扩散方程的紧致修正方法,该方法是在低阶离散格式的源项中,引入紧致修正项,从而构造高阶紧致修正格式,并进行求解.采用紧致修正方法对典型的对流扩散方程进行计算.结果表明,紧致修正方法虽然与二阶经典差分方法建立在相同的结点数上,但紧致修正方法的精度与紧致方法的精度相同,均具有四阶精度.所以紧致修正方法可以在少网... 相似文献
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求解Navier-Stokes方程组的组合紧致迎风格式 总被引:1,自引:0,他引:1
给出一种新的至少有四阶精度的组合紧致迎风(CCU)格式,该格式有较高的逼近解率,利用该组合迎风格式,提出一种新的适合于在交错网格系统下求解Navier-Stokes方程组的高精度紧致差分投影算法.用组合紧致迎风格式离散对流项,粘性项、压力梯度项以及压力Poisson方程均采用四阶对称型紧致差分格式逼近,算法的整体精度不低于四阶.通过对Taylor涡列、对流占优扩散问题和双周期双剪切层流动问题的计算表明,该算法适合于对复杂流体流动问题的数值模拟. 相似文献
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封闭圆内开缝圆自然对流换热的振荡特性 总被引:1,自引:0,他引:1
本文通过数值计算探讨了封闭圆内开缝圆自然对流换热的振荡特性。数值计算以整个圆为计算区域,采用了非稳态的数学模型和具有QUICK差分格式的SIMPLE算法。在相同条件下计算结果和实验结果符合很好。数值结果显示, 当几何结构一定时,Rayleigh数Ra小于某个临界值时,流动和换热处于稳态,并且关于垂直中心线对称;Ra大于这个临界值时,流动和换热是振荡的,非对称的。数值实验还表明,流动和换热出现振荡时的临界Rayleigh数Rac与开缝圆的开缝度有关,且流动和换热的振荡会出现对称振荡和非对称振荡两种情形。 相似文献
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A detailed numerical modeling is performed to investigate coupled heat transfer of natural convection, radiation and conduction in high-temperature multilayer thermal insulation (MTI), which consists of high-porous, non-gray semitransparent fibrous materials and reflective foils. Radiation within fibers, radiation between fibers and the reflective foils, conduction within fibers and convection from the fibers to the surrounding fluid are considered. Macroscopic (porous media) modeling is used to determine velocity, pressure and temperatures fields for fibrous insulation with a random packing geometry under natural convection, whereas the radiative transfer equation (RTE) is used to solve the radiative heat flux for non-gray materials. Key features of the macroscopic model include two-dimensional effects, non-gray radiative exchange, and the relaxation of the local thermodynamic non-equilibrium (LTNE). This model was validated by comparison with experimental data and it was used to investigate natural convection of coupled heat transfer in multilayer insulation, numerical results showed that natural convection is more likely to occur when the heated/cooled rate is low, while natural convection can be ignored in simulating steady-state coupled heat transfer in MTI. 相似文献
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In the present study, mathematical modeling was performed to simulate natural convection of a nanofluid in a square enclosure using the thermal lattice Boltzmann flux solver (TLBFS). Firstly, natural convection in a square enclosure, filled with pure fluid (air and water), was investigated to validate the accuracy and performance of the method. Then, influences of the Rayleigh number, of nanoparticle volume fraction on streamlines, isotherms and average Nusselt number were studied. The numerical results illustrated that heat transfer was enhanced with the augmentation of Rayleigh number and nanoparticle volume fraction. There was a linear relationship between the average Nusselt number and solid volume fraction. and there was an exponential relationship between the average Nusselt number and Ra. In view of the Cartesian grid used by the immersed boundary method and lattice model, the immersed boundary method was chosen to treat the no-slip boundary condition of the flow field, and the Dirichlet boundary condition of the temperature field, to facilitate natural convection around a bluff body in a square enclosure. The presented numerical algorithm and code implementation were validated by means of numerical examples of natural convection between a concentric circular cylinder and a square enclosure at different aspect ratios. Numerical simulations were conducted for natural convection around a cylinder and square in an enclosure. The results illustrated that nanoparticles enhance heat transfer in higher Rayleigh number, and the heat transfer of the inner cylinder is stronger than that of the square at the same perimeter. 相似文献
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Natural convection heat transfer in the presence of a magnetic field has received considerable attention in the past few decades because of its various applications in industrial installations. In particular, a large number of numerical studies analyzing the effect of the magnetic field on natural convection in a two-dimensional cavity have been performed. In this work, we propose to study the main characteristics of the convective heat transfer of pure fluids and nanofluids in a two-dimensional cavity differentially heated and subjected to an external magnetic field. The scale analysis method is used first to obtain a correlation giving the heat transfer rate, which is then developed to predict the behavior of the heat transfer rate for pure fluids and nanofluids. To verify the reliability of the theoretical predictions, a numerical study is also carried out. The results show that the proposed correlation predicts well the convective heat transfer characteristics obtained numerically. 相似文献
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The natural convection flow phenomena that occur inside an enclosed space are very interesting examples of complex fluid systems
that may yield to analytical, empirical and numerical solutions, and many reports have looked into this basic problem. In
the present study, heat transfer and fluid flow for natural convection in a horizontal rectangular container with a free surface
are investigated using infrared thermography. The temperature field was measured and visualized at a gas-liquid (air — silicon
oil) interface using infrared thermography. The heat transfer phenomena were also investigated by statistically analyzing
the temperature data. The applicability of the infrared thermography to quantitative heat transfer measurement at the gas-liquid
interface was evaluated. It is revealed that infrared thermography is effective not only in visualization of a gas-liquid
interface but also in heat transfer measurement. A new heat transfer correlation is proposed for the gas-liquid interface
of this flow system. The coefficient of heat transfer can be summarized by a specific heat transfer correlation formula regardless
of several conditions, including container aspect ratio, fluid viscosity and fluid layer depth. 相似文献
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合金凝固过程中存在于枝晶尖端液相区的强制对流和自然对流均能改变溶质扩散层厚度,从而会对枝晶形貌产生较大影响.在元胞自动机模型基础上,耦合液体流动方程、热传导方程和溶质对流扩散方程,建立了新的计算微观组织演化的数值模型,并利用该模型研究了强制对流和自然对流对枝晶生长的影响.三维数值模拟结果再现了强制对流作用下等轴枝晶的生长过程,揭示了强制对流对枝晶生长速率和尖端半径的影响特点.同时利用该模型模拟了NH4Cl-H2O溶液定向凝固过程中自然对流对柱状晶生长的影响,并采用相应的实验进行验证.模拟结果与实验结果符合良好,从而证明该模型是可靠的,可推广到实际合金系中.
关键词:
元胞自动机
对流
4Cl-H2O溶液')" href="#">NH4Cl-H2O溶液
定向凝固 相似文献