Numerical investigation of the adverse effect of wind on the heat transfer performance of two natural draft cooling towers in tandem arrangement

This article reports the findings on the adverse effect of the crosswind on the performance of natural draft cooling towers through numerical computation with thek-ε eddy-viscosity turbulence model. It is observed here that the cause of the adverse effect of the crosswind on the cooling towers can be attributed to the around flow effect which destroys the radial inflow into the cooling towers when the wind is absent. Hence, a significant deterioration in the heat transfer from the heat exchangers at lateral sides occurs. The project supported by the National Natural Science Foundation of China (19725208) and the National Climbing project of China     

A block‐implicit numerical procedure for simulation of buoyant swirling flows in a model furnace

This work reports numerical results for the case of incompressible laminar heated flow with a swirl in a vertical cylindrical chamber. Computations are obtained with a point‐wise block‐implicit scheme. Flow governing equations are written in terms of the so‐called primitive variables and are recast into a general form. The discretized momentum equations are applied to each cell face and then, together with the mass‐continuity, tangential velocity and energy equations, are solved directly in each computational node. The effects of Rayleigh, Reynolds and Swirl numbers on the temperature field are discussed. Flow pattern and scalar residual history are reported. Further, it is expected that more advanced parallel computer architectures can benefit from the error smoothing operator here described. Copyright © 2003 John Wiley & Sons, Ltd.     

电子枪加热合金熔池的数值分析

利用数值方法求解了电子枪加热二维合金熔池的流体力学方程组，获得了熔池流场的速度、温度和浓度分布.并且详细地研究了各种特征参量（如雷诺数、普朗特数、格拉晓夫数和李斯特数）对合金熔池流动特性的影响，一般地，雷诺数和普朗特数越小、而格拉晓夫数和李斯特数越大，则熔池中溶剂金属的蒸发速率就越大.在此基础上提出参杂适当浓度的溶质金属可以提高某些难熔难挥发金属的蒸发速率，计算中对参杂了钨、钕、锡和铬等金属的钍、铂、铱和钌等合金熔池进行了数值分析，都相应提高了溶剂金属的蒸发速率. 关键词： 液态合金 毛细流 浮力流 熔池     

非保守力与自然对流

为研究自然对流流动和换热的实质,对重力场中自然对流的驱动力进行了进一步分析,提出了自然对流产生的充分必要条件。以二维封闭方腔内空气自然对流为对象,分别对三种不同的自然对流形式进行了数值模拟。结果表明:只要流体所受体积力为非保守力,即可产生自然对流。这为自然对流的控制提供了一定的理论依据。     

"显压浮子"实验装置

为了弥补现行教科书中浮力产生原因的知识呈现的不足,设计了符合学生认知规律的正方体显压浮子实验装置.该装置的特征是通过“U”型压强计系统能够在正方体上直接显示上下表面所受压强不同,从而形象地表明浮力产生的原因.     

Large-eddy simulation of stratified channel flow

An investigation of large-eddy simulation (LES) for turbulent channel flow with buoyancy effects was performed by solving the resolved incompressible Navier-Stokes equations under the Boussinesq approximation. The Smagorinsky eddy-viscosity model and Yoshizawa eddy-viscosity model were used to describe the unresolved subgrid scale (SGS) fluctuations respectively. After some numerical testing, the latter was further simplified so that it can be used in the dynamic model closure. A LES code was developed for parallel computations by using the parallel technique, and was run on the Dawn-1000 parallel computer. To demonstrate the viability and accuracy of the code, our results are compared with and found in good agreement with available LES results. The project supported by the National Natural Science Foundation of China and by the Youngster Funding of Academia Sinica     

凝固界面前沿自然对流的实验研究

本文在水平Bridgman定向凝固装置中,对超薄试样中固液界面前沿的自然对流进行了实验研究。发现在厚度仅为200μm—700μm的试样中,由于水平温度梯度的存在,凝固界面附近仍然存在着不可忽视的自然对流,并系统研究了各种不同因素对界面前沿热对流的影响规律,为界而过程的微观分析和凝固理论的研究提供了丰富的信息,为采用该装置进行透明有机物模拟研究提供了设计依据。     

水浮力对浮桥动力响应特性的分析

为了研究水介质的浮力对桥梁静态响应、特别是动态响应的影响,了解水浮力在桥梁动力响应上的作用及其大小,利用虚功原理和振型叠加法对桥梁运动的控制方程进行求解,并编制了通用的求解程序,通过对比简支梁桥和浮桥各阶振型的传播速度、静力作用、单阶荷载作用以及移动荷载作用下的动力响应,得出水浮力的存在大大降低了浮桥的挠度,使得浮桥的动力响应存在临界长度,即简支梁桥的运动整体性强,而浮桥的运动局部性强,对浮桥进行动力分析时,可以在临界长度以内进行处理,而不必对整个桥梁进行求解.     

CFD Analysis of a Thermal Plume and the Indoor Air Flow Using k-ε Models with Buoyancy Effects

Turbulence models based on the eddy viscosity concept perform poorly for simulation of non-isothermal flows, which are characterized by strongly non-isotropic features of turbulence. In the present study, a thermal plume is calculated using the WET model and severalk-ε models. Comparison with the experiments reveals that the WET model predicts the flow and temperature fields most accurately. Furthermore, the WET model has been modified to account for the damping effect near the wall and applied to the indoor air flow. The computed flow field agrees well with the measurement, except for higher temperatures appearing near the walls. This revised version was published online in July 2006 with corrections to the Cover Date.     

Flame Surface Density in Turbulent Premixed V-Flame with Buoyancy

A fractional step numerical model is established for turbulent premixed combustion with buoyancy. The flame front propagation is described by the level-set method. Simulated results without buoyancy have been previously validated with available experimental data on a premixed V-flame. A new formula is presented to fit the flame surface density with respect to the reaction progress variable in a turbulent premixed V-flame. By numerical simulations, dynamical behaviour of the flame under the interaction of turbulence, exothermicity and buoyancy are investigated.