Influence of the heating rate on the critical Marangoni number of oscillatory thermocapillary convection in the floating half zone

In the present study, numerical simulations were conducted on thermocapillary convection in floating half zones of 5 cSt silicone oil of different scales in comparison with the experimental studies in the microgravity conditions. The effect of heating rate on the marginal instability boundaries is indicated as a possible explanation for the significant quantitative discrepancies between the experimental results in the terrestrial conditions and in the microgravity conditions.

Finite element solution of nonlinear convective flow of Oldroyd-B fluid with Cattaneo-Christov heat flux model over nonlinear stretching sheet with heat generation or absorption

In this study,a two-dimensional boundary layer flow of steady incompressible nonlinear convective flow of Oldroyd-B fluid over a nonlinearly stretching sheet with Cattaneo-Christov heat flux model and heat generation or absorption is examined.The governing equations of the boundary layer flow which are highly nonlinear partial differential equations are converted to the ordinary differential equations using similarity transformations and then the Galerkin finite element method(GFEM)is used to solve the proposed problem.The effect of local Deborah numbers 0,and ft.local buoyancy parameter z,Prandtl number Pr,Deborah number y,and heat generation/absorption parameter<5 on the temperature and the velocity as well as heat transfer rate and shear stress are discussed both in graphical and tabular forms.The result shows the enlargement in the local buoyancy parameter A will improve the velocity field and the heat transfer rate of the boundary layer flow.Moreover,our present work evinced both local skin friction coefficient and heat transfer rate step up if we add the values of non-linear stretching sheet parameter and local heat generation/absorption parameter has quite the opposite effect.The numerically computed values of local skin friction coefficient and local Nusselt number are validated with available literature and evinced excellent agreement.

微重力下单晶硅生长中热毛细对流的控制研究

在微重力条件下用浮区结晶法生长半导体单晶硅独具优势 ,但自由界面的温度梯度所诱发的热毛细对流对晶体质量的影响却更为突出。文中提出一种抑制热毛细对流的新方法———表面截割法 ,即通过适当改变自由表面的状况来抑制热毛细对流 ;在建立了半浮区 (液桥 )热毛细对流的数学模型的基础上 ,利用有限元法对不同截割方式下的流场、温度场做了数值模拟分析。结果表明 ,表面截割对浮区内的热毛细对流有很好的抑制作用 ,适当增加截割次数 ,可使热毛细对流削弱 70 %以上。

上地幔变黏度小尺度对流的数值研究

基于二维模型 ,利用有限元方法 ,研究上地幔 -岩石圈系统的变黏度小尺度对流 .考虑该系统的黏度随温度以指数形式变化 ,数值结果表明 ,当黏度随温度变化较剧烈时 ,由于低温高黏度 ,系统的最上部物质不参与对流 ,系统发育形成一个类似于岩石圈的静止盖层 .计算表面热流、地形起伏及重力异常与对流格局有较好的相关性 ,高热流、上升地形对应于对流的上升区 ,反之低热流、下降地形与对流的下降区对应 .

粘性流体圆柱绕流的有限元模拟

对粘性流体圆柱绕流进行了数值模拟。根据三阶Taylor展开弱解的概念，在二阶分裂步Taylor－Galerkin有限元法基础上，采用时间推进和张量分析的方法推导了对流扩散通用微分方程的ETG有限元离散格式。对Reynolds数为32、102和250的粘性流体圆柱绕流流场进行了数值仿真，数值模拟结果与实验结果吻合良好。表明隐含流线迎风耗散作用并具有三阶部分展开的Taylor－Galerkin有限元法稳定性好，精度较高，可用于计算包含对流扩散耦合传递动量的绕流问题及类似的流动问题。

强制空气对流换热条件下的带式输送机盘式制动器传热分析

为提升自冷式盘式制动器的散热能力,增设强制通风结构,在强空气对流换热条件下研究该制动盘的传热特性。分别采用解析法和有限元数值模拟方法求解出制动盘的一维稳态过余温度场和三维瞬态温度场,并基于台架试验方法校验瞬态温度场的计算精度。结果表明:试验结果与仿真结果具有良好的匹配性;对流换热系数对于盘体温度场的影响是非线性的,随着强制对流换热系数的增大,传热方向上的温度梯度将显著增大,散热效率更高。通过强制通风来增大对流换热系数对于大运载能力的带式输送机制动器而言,具有良好的可靠性和经济性。

Linear Stability Analysis of Thermocapillary Flow in Rotating Shallow PoolsHeated from Inner Wall

Thermocapillary flow of silicon melt(Pr=0.011)in shallow annular pool heated from inner wall was simulated at the dimensionless rotation ratewranging from 0 to 7000.The effect of pool rotation on the stability of the thermocapillary flow was investigated.The steady axisymmetric basic state was solved by using the spectral element method;the critical stability parameters were determined by linear stability analysis;the mechanism of the flow instability was explored by the analysis of energy balance.A stability diagram,exhibiting the variation of the critical Marangoni number versus the dimensionless rotation ratewwas presented.The results reveal that only one Hopf bifurcation point appeared in the intervals ofω<3020 andω>3965,and the corresponding instability was caused by the shear energy,which was provided by the thermocapillary force and pool rotation,respectively.In addition,the competition between thermocapillary force and pool rotation leads to three Hopf bifurcation points in the range of 3020<ω<3965 with the increase of Marangoni number.

强对流问题数值计算的一种迎风有限元方法

采用 Green定理将有限元积分方程中的对流项变量从微分算子中分离出来 ,从插值函数入手建立迎风格式 ,解决了在 Galerkin有限元方法中不易引入迎风格式的问题。通过建立局部斜迎风格式及对几个典型问题的数值模拟 ,表明了该方法用于对大 Peclet数流动及复杂区域流动的数值模拟是可行的。

基于Krylov子空间的微混合器宏模型设计与仿真

获得宏模型是微混合器设计与仿真的关键。将Navier-Stokes方程和对流扩散方程用有限元方法进行离散化处理,应用Krylov子空间的Arnoldi过程对得到的微分-代数方程组降阶处理,提取出宏模型。仿真结果表明,经过降阶处理得到的宏模型保证了微混合器的输出精度,降低了计算复杂度。

Heat and mass transfer of a circular porous moist object located in a triangular shaped vented cavity

Heat and mass transfer of a circular-shaped porous moist object inside a two-dimensional triangle cavity is investigated by using finite element method.The porous object is considered to be a moist food sample,located in the middle of the cavity with inlet and outlet ports with different configurations of inlet/outlet ports.Convective drying performance is numerically assessed for different values of Reynolds numbers(between 50 and 250),dry air inlet temperature(between 40 and 80℃)and different locations of the port.It is observed that changing the port locations has significant impacts on the flow recirculaitons inside the triangular chamber while convective drying performance is highly affected.The moisture content reduces with longer time and for higher Reynolds number(Re)values.Case P4 where inlet and outlet ports are in the middle of the walls provides the most effective configuration in terms of convective drying performance while the worst case is seen for P1 case where inlet and outlet are closer to the corners of the chamber.There is a 192% difference between the moisture reduction of these two cases at Re=250,T=80℃ and t=120 min.

Numerical Study of Mixed Convective Peristaltic Flow through Vertical Tube with Heat Generation for Moderate Reynolds and Wave Numbers

The current study focuses on the numerical investigation of the mixed convective peristaltic mechanism through a vertical tube for non-zero Reynolds and wave number. In the set of constitutional equations, energy equation contains the term representing heat generation parameter. The problem is formulated by dropping the assumption of lubrication theory that turns the model mathematically into a system of the nonlinear partial differential equations. The results of the long wavelength in a creeping flow are deduced from the present analysis. Thus, the current study explores the neglected features of peristaltic heat flow in the mixed convective model by considering moderate values of Reynolds and wave numbers. The finite element based on Galerkin's weighted residual scheme is applied to solve the governing equations. The computed solution is presented in the form of contours of streamlines and isothermal lines, velocity and temperature profiles for variation of different involved parameters. The investigation shows that the strength of circulation for stream function increases by increasing the wave number and Reynolds number. Symmetric isotherms are reported for small values of time-mean flow. Linear behavior of pressure is noticed by vanishing inertial forces while the increase in pressure is observed by amplifying the Reynolds number.

计算平流过程的一种高精度离散格式及数值试验

该文提出了一种用泰勒-伽辽金有限元法进行数值模拟的高精度离散格式。应用此格式在旋转流场中对二维纯平流问题浓度场的变化进行了数值试验,并同迎风格式、Crank-Nicolson格式、Lax-Wendroff格式、蛙跳格式的数值模拟结果进行了对比分析。数值试验结果表明:该离散格式具有较高的精确度和较好的稳定性,还具有求解速度快、位相误差小的优点,适合应用于平流过程的高质量的模式中。