气体横掠单管强制对流换热的大涡模拟

应用大涡模拟与二价全展开ETC有限元离散格式相结合的方法对气体横掠单管强制对流换热进行了数值模拟,分别计算了气体横掠团管和方管时的温度场,得到了管壁平均换热系数,数值结果与实验关联式符合较好。同时还表明大涡模拟方法善于捕捉温度场以及流场涡系的时间演化过程,非常适合于具有大尺度涡的绕流运动温度场的分析。     

骨架导热特性对部分填充多孔介质复合腔体内传热影响的模拟研究

利用有限元数值方法对部分填充多孔介质复合腔体内的自然对流进行模拟研究,模拟利用两区域法来计算复合腔体内的自然对流,在多孔介质区域采用Forheimer-Brinkman-Darcy方程,在纯流体区域使用Navier-Stokes方程,重点研究了多孔介质骨架导热特性对自然对流的影响。研究发现,在一定范围内随着多孔介质导热性的增强,流体温度升高,部分填充多孔介质腔体内自然对流有一定程度的增强。     

应用热非平衡模型模拟梯度磁场作用下多孔介质方腔内空气热磁对流

梯度磁场可用来控制多孔介质内空气的自然对流传热过程.利用局部热非平衡模型对圆形截流线圈水平放置时三维多孔介质方腔内的空气热磁对流进行了数值研究.控制方程基本变量采用控制容积法离散,求解采用SIMPLE算法.计算过程中Ra为103～105,磁场力数γ为0～150、Da为10-7～100.获得了空气热磁对流的流场和温度场....     

含热源方腔的耦合自然对流换热的三维数值模拟

对具有内热源方腔的稳态层流耦合自然对流换热进行了三维的数值模拟，采用的模拟代码基于连续介质计算力学的开源库OpenFoam，解决了自然对流换热与固体传热的耦合问题。对外壁面为常温、方腔内充满含体积热源流体的自然对流计算结果表明，温度场、速度场与非耦合的工况有很大差异。     

壁面覆盖部分多孔介质方腔自然对流流动的数值模拟

多孔介质壁面封闭腔体的自然对流在生产实际中有重要的应用。针对左侧部分多孔介质壁面方形封闭腔体,基于有限元法对封闭腔体的自然对流换热进行了数值模拟,得到了在不同Ra、孔隙率条件下腔体内空气的温度分布、速度分布。结果表明:随着Ra的增大,腔体内的流场及温度场发生了明显的变化,多孔介质壁面孔隙率的变化对腔体的流动换热的影响很小。     

不同磁场布置对空气自然对流的影响

为研究顺磁性气体介质在外磁场作用下自然对流换热的规律，进一步揭示热磁对流的实质，该文用数值方法模拟了两种钕铁硼永磁系统产生的磁场作用下二维封闭方腔内空气的自然对流换热，得到了工作空间内磁场强度和磁加速度的分布，获得了两种梯度磁场作用下空气自然对流的流场和温度场以及壁面局部对流换热系数。研究表明，不同的永磁系统布置可在工作空间形成不同的磁加速度分布，产生不同的磁场力，从而影响空气自然对流换热的强弱。     

含体积热源方腔的耦合自然对流换热数值模拟

对具有内热源方腔的稳态层流耦合自然对流换热进行了三维的数值模拟，采用的模拟代码基于连续介质计算力学的开源库OpenFoam，解决了自然对流换热与固体传热的耦合问题。对外壁面为常温、方腔内充满含体积热源流体的自然对流计算结果表明，温度场、速度场与非耦合的工况有很大差异。Ra的变化从10^5到10^9。     

利用移动网格技术模拟冰融化过程中的传热问题

用计算流体动力学中的贴体坐标下移动网格技术分析了一类典型具有移动界面的流动融化传热问题，即Stefan问题。流场的计算采用控制容积法，控制方程的离散扩散项采用中心差分法，对流项采用QUICK格式。通过计算表明，这种技术可以非常好地捕捉由于融化引起的界面运动和变形的位置，能获得准确的融化曲线及温度场的演化过程。从中可总结出努谢尔特效或传热系数的变化趋势，找出在自然对流情况下，方冰柱的融化规律和固液界面形状的变化。     

采用热-流耦合方法对火焰筒壁温三维数值模拟

考虑了流场变化对换热的影响,使用热-流耦合方法,对某型燃烧室整个流场、温度场进行完全的数值模拟。该方法对流场和固壁内换热进行耦合计算,得出了三维燃烧室壁温分布。计算中,对完全发展的湍流燃气采用了标准“k-ε”湍流模型,运用DO模型计算了燃气的热辐射,燃烧模型使用涡-耗散模型来计算化学反应速度,固壁材料使用了变比热和变导热系数。数值模拟结果表明流场与固壁相互作用得更充分,能更精确地反映流场和温度场的整个形态,可以模拟出较为合理的流场和温度场分布以及相应的流动换热特性。     

低散热发动机对流散热场的数值分析

本文利用在非交错网格上求解非正交曲线上标系下的Ｎ－Ｓ方程的方法，对低散热发动机对流散热场进行了数值模拟，得到了不同瑞利（Ｒａｙｌｅｉｇｈ）数下的散热通道内流场和温度场的数值解。计算结果表明，通过冷却通道中空气自然对流换热方式所散失的热量很小。     

Multiple steady states for natural convection in a shallow porous cavity subject to uniform heat fluxes

Multiplicity of steady states in natural convection within a shallow porous cavity, exposed to uniform heat fluxes on all sides, is investigated. Analytical solution for the stream function and temperature fields, in the central region of the cavity, is obtained using a parallel flow assumption. It is demonstrated that multiple steady states are possible, some of which are unstable. A finite difference method is used to obtain numerical solutions of the full governing equations. A good agreement is observed between the analytical predictions and the numerical simulations.     

Projection- and characteristic-based operator-splitting simulation of mixed convection flow coupling heat transfer and fluid flow in a lid-driven square cavity

ABSTRACT

Mixed convection flow in a 2D rectangular cavity is simulated by a novel finite element method, namely the projection- and characteristic-based operator-splitting algorithm. In each time step, the Navier–Stokes equations are split as follows: the diffusion part, the convection part by applying operator-splitting method, and the Poisson’s equation by adopting projection method. The implicit diffusion part is solved by the preconditioned conjugate gradient (PCG) method, whereas characteristic method is applied for the convection part in a multistep explicit scheme. The characteristic Galerkin approach is used to solve the energy equation. To validate the model, lid-driven cavity flow and natural convection flow are simulated.     

Numerical study of the heat and mass transfer in inclined glazing cavity: Application to a solar distillation cell

A numerical analysis is performed for the natural convection flow resulting from the combined buoyancy effects of thermal and mass diffusion in an inclined cavity. This work enters within the framework of general study dealing with the mathematical model for solar brackish water desalination unit. The problem is stated in a Cartesian coordinates system, involves the use of a control volume-based finite-element method and solves the full vorticity transport equation together with the stream function, concentration and energy equations. The predicted stream function patterns, isoconcentration and isotherms are presented for different thermal Rayleigh numbers. The heat and mass transfer evolution are explained in terms of dynamic and temperature fields of the flow in the inclined cavity. In particular, the desirable flow for enhancing the performance of the solar distiller is determined by examining flow patterns.     

Numerical investigation of coupled natural convection and radiation in a differentially heated cubic cavity filled with humid air. Effects of the cavity size

A numerical study of natural convection with surface and air/H₂O mixture radiation in a differentially heated cubic square cavity is presented. The coupled flow and heat transfers in the cavity are predicted by coupling a finite volume method with a spectral line weighted sum of gray gase model to describe gas radiative properties. The radiative transfer equation is solved by means of the discrete ordinate method. Simulations are performed at Ra?=?10⁶, considering different combinations of passive wall and/or gas radiation properties and different cavity length. It was found that in presence of a participative medium representative of building, cavity length has a strong influence on temperature and velocity fields which affect the global circulation and heat transfers in the cavity. For each steady-state solution, the convective and radiative contributions to the global heat transfer are discussed. More specifically, boundary layer thickness, thermal stratification parameter, and three-dimensional effects are compared to pure convective case results. The results suggest that radiative effects, often considered as negligible in view of the relatively low optical thickness, may not be neglected when trying to predict regime transitions.     

Spectral Fourier–Galerkin benchmark solution for natural convection in an inclined saturated porous medium

This paper presents some novel problems associated with the steady natural convection flow in an inclined square cavity filled with a saturated porous medium. The proposed method is a high-accurate spectral method based on the Fourier–Galerkin technique. The numerical results have demonstrated the advantage for the following reasons. (a) The high-accurate method deals with inclined geometries successfully. (b) The streamlines, isotherms, and the average Nusselt numbers are affected significantly by the inclination of the cavity for high values of Rayleigh number. (c) In contrast with the finite element method a highly accurate and efficient solution with less computational effort is obtained.     

Application of Program Generation Technology in Solving Heat and Flow Problems

Based on a new DIY concept for software development,an automatic program-generating technology attached ona software system called as Finite Element Program Generator(FEPG)provides a platform of developing pro-grams,through which a scientific researcher can submit his special physico-mathematical problem to the systemin a more direct and convenient way for solution.For solving flow and heat problems by using finite elementmethod,the stabilization technologies and fraction-step methods are adopted to overcome the numerical difficul-ties caused mainly due to the dominated convection.A couple of benchmark problems are given in this paper asexamples to illustrate the usage and the superiority of the automatic program generation technique,including theflow in a lid-driven cavity,the starting flow in a circular pipe,the natural convection in a square cavity,and theflow past a circular cylinder,etc.They are also shown as the verification of the algorithms.     

SOLUTION OF TRANSIENT LAMINAR NATURAL CONVECTION IN A SQUARE CAVITY BY AN EXPLICIT FINITE ELEMENT SCHEME

This paper discusses the application of a finite element method based on the first-order projection scheme, which is an extension ofChorin's algorithm, to transient laminar natural convection in a square cavity. Results have been presented for a fluid of Prandtl number 0.71 in the Rayleigh number range of 10³-10⁶ in terms of the variation of vertical velocity component, nondimensional temperature, and average Nusselt number with time. Various features of the scheme that render it economical in terms of CPU time and storage requirements are discussed. The steady state results have been compared with benchmark solutions, and the agreement appears to be good.     

Transient natural convection with temperature-dependent viscosity in a square partially porous cavity having a heat-generating source

A numerical study is performed on the transient natural convection with a temperature-dependent viscosity inside a square partially porous cavity with a local heat-generating and heat-conducting source. The vertical walls of the cavity are kept at constant cooling temperature while the horizontal walls are adiabatic. The discrete heat-conducting and heat-generating source is located on the bottom wall. A porous layer is located under the clear fluid layer. Governing equations formulated in dimensionless stream function, vorticity and temperature variables with corresponding initial and boundary conditions are solved using implicit finite difference schemes of the second order. The control parameters are the Darcy number, Ostrogradsky number, viscosity variation parameter, height of the porous layer, and dimensionless time. The effects of these parameters on the average Nusselt number along the heat source surface, average temperature of the heater, fluid flow rate inside the cavity, as well as on the streamlines and isotherms are analyzed. The results show that porous layer thickness and viscosity of the working fluid are very good control parameters for optimization of the passive cooling system.     

Buoyancy-induced flow,heat, and mass transfer in a porous annulus

This paper reports on double-diffusive natural convection heat transfer in a porous annulus between concentric horizontal circular and square cylinders. A pressure-based segregated finite volume method is used to solve the problem numerically. The diffusion fluxes are discretized using the MIND fully implicit scheme. Furthermore, a modified pressure correction equation is derived that implicitly accounts for the nonorthogonal diffusion terms, which are usually neglected in the standard SIMPLE algorithm. Results indicate that convection effects increase with an increase in Rayleigh number, Darcy number, porosity, and enclosure aspect ratio. Further, at low Darcy values, porosity has no effect on the flow, temperature, and concentration fields.