孔板空调风口送风射流的数值模拟

介绍Ｎ点风口模型用于数值模拟室内空气流动时描述孔板类送风口的入流边界条件．然后采用该风口模型对不同的孔板风口出流条件算例进行数值计算,并就轴心速度衰减、射流扩展角以及断面流速分布等射流特性与实验数据进行了对比．比较结果表明,Ｎ点风口模型用于描述数值模拟室内空气流动的孔板类风口入流边界条件,可以获得工程上足够满意的结果．     

方型散流器空调室内空气流动的数值模拟

用N点风口动量模型和一个新零方程湍流模型对某办公室方型散流器空调的室内温度场和速度场进行了模拟,并和实验数据进行对比.结果表明,计算所得速度和温度分布与实测值吻合得很好,所用的风口模型和湍流模型能快速地将方型散流器空调通风的温度和速度场合理地模拟出来,可用于指导和优化同类空调通风气流组织设计.     

置换通风的数值模拟

首先介绍了用于数值模拟置换通风室内空气分布的N点风口模型、新零方程湍流模型，以简化和加快实际工程中对置换通风的模拟计算。然后利用这些模型对某办公室置换通风的室内温度场和速度场进行了模拟，并和实验数据进行对比。结果表明，计算所得速度和温度分布与实测值吻合得很好，所用的风口模型和湍流模型能将置换通风的温度分层特性和速度场合理地模拟出来，可用于指导和优化置换通风气流组织设计。     

多层建筑屋顶风场的数值模拟

基于计算流体动力学软件Fluent17.2,以浙江温州大学某栋带女儿墙的多层试验教学楼为研究对象,采用RNG k-ε湍流模型对其进行数值模拟.通过对不同风向角下的数值模拟结果进行对比分析,探究屋顶风场与未受扰来流风场的区别,屋顶不同高度风场的差异,以及不同风向角来流情况下近屋面风场的分布特点、变化规律.结果表明:在离屋面高8m以下,屋顶风速变化剧烈混乱,屋面前沿、中部、后方区域的风速会随高度增加发生变化,并与未受扰来流风场相比存在较大差别;在女儿墙高度1.2m以下,屋面四周区域风速小于中部区域;在离屋面高1.2m～8m时,同一高度屋面前沿区域风速却要大于中部区域及后方区域;在不同的风向角来流下,当来流与建筑迎风面垂直时,屋顶风场沿中线对称分布.本文所得结论可为屋顶各类设备的抗风设计提供一定的参考依据.     

液氮过冷流动沸腾数值模拟中的双流体模型

液氮过冷流动沸腾广泛见于各种低温换热设备中.采用双流体模型分析液氮过冷流动沸腾,需要为模型提供适当的封闭方程,用于描述汽液两相间质量、动量以及能量的传输过程,封闭方程的合理性直接决定了双流体模型的准确性.将液氮流动沸腾通道划分为近壁区和主流区,分别介绍液氮核态沸腾壁面上的传热传质机理模型,以及两相流程内汽液之间的相互作用的相间传输模型,建立液氮流动沸腾过程适用的双流体模型,并分析了对模型预测能力具有显著影响的因素,指出存在的问题和解决方案.      

基于CFD-DEM的高炉风口回旋区形状和传热特性数值模拟研究

采用计算流体力学-离散单元法(CFD-DEM)耦合方法,对高炉风口回旋区进行了数值模拟研究。首先通过与实验结果对比,验证了CFD-DEM模型的正确性;然后考察了不同气速对风口回旋区形状和传热特性及颗粒接触的影响。数值模拟结果表明:风口回旋区的大小和形状均受气速影响较大,在较大进气速度下,颗粒受到的曳力大于颗粒间的摩擦阻力并破坏颗粒间的桥力,形成较大尺寸的回旋区;且颗粒之间接触力较小,形成较大的空隙结构,更有利于热气体向周围扩散以强化传热。目前考察的三种气速结果表明:当气速为11m/s时,热量向下方传递速度最快;当气速为13m/s时,热量向上方传递速度最快;而当气速为15m/s时,热量向右方传递速度最快;此外,气速越大流态化越明显,颗粒间接触越少,接触力也越小。     

分离流动数值模拟的几个问题

介绍了分离流动现象.给出了三维定常粘性流动分离识别准则,研究了分离流动的性态.给出了应用于分离流动的六种模型及有关的控制方程.讨论了求解NS方程的数值方法和数值模拟的前景.特别研究了应用于分离流动的Eulcr方程的数值模拟问题.     

井内流动与传热的三维耦合数值模型

钻井过程中,井内的压力、流场及温度分布是钻井作业必需的重要参数.本文提出了一个描述井内流动和传热的三维数学模型,用SIMPLER方法获得了该数学模型的数值解.该数值模型考虑了温度、压力对钻井液的流变性、密度以及各种介质的热物理参数的影响.现场试验数据与数值模拟结果的对比表明:本文提出的数学模型及采用的数值计算方法是可行的.     

载人列车车厢内空气流场温度场数值模拟

采用稳态不可压缩雷诺时均N-S方程、k-ε湍流模型,计算了载人列车车厢内三维空气流场和温度场.将太阳辐射热和人体散热作为能量方程的附加源项,研究了在条缝送风条件下,乘客和太阳辐射对车厢内流场和温度场的影响.计算结果表明:现有的送风方式除车厢两端外,车厢内沿长度方向气流分布比较均匀;送风口的布置对车厢内流场温度场分布影响较大,送风气流在车厢两侧形成两股比较大的流动旋涡;人体散热和太阳辐射对车厢内流场温度场影响较大,非空载时车厢内流场分布与空载时有较大差别,太阳照射和人体产生的热气流使车厢内存在较大的温度梯度,靠窗处的温度较高,过道处温度较低.流场温度场的计算结果和实验数据吻合较好.     

三维湍流流动的涡量-向量势法数值模拟

本文采用涡量-向量势法,结合常规的 k-ε双方程湍流模型,并运用重新推导的固体壁面涡量边值计算法,对扁平射流煤粉燃烧器内的冷态三维流场进行了数值模拟。计算结果与实验数据相吻合。本文工作证明,用涡量-向量势法求解三维湍流问题是可行的,该法具有不应忽视的优越性,值得进一步开发。     

空气炮碰撞实验台发射过程的数值模拟

利用计算流体动力学方法对单级空气炮碰撞实验台的发射过程进行了数值仿真,所得碰撞车发射速度与实验结果吻合。在此基础上,对碰撞车发射过程的流场变化、车体前后压力以及储气罐压力变化进行分析。结果表明,泄漏气体先于碰撞车充满整个发射空间,形成初始流场,使得车前压力出现正负交替现象,但其数值较小,对车体加速过程的影响可以忽略。当碰撞车进入泄压段后,受冲击射流作用,碰撞车仍处于加速状态,且速度增量约为2 m/s。

     

Multi‐resolution analysis for high accuracy and efficiency of Euler computation

A multi‐resolution analysis (MRA) is proposed for efficient flow computation with preserving the high‐order numerical accuracy of a conventional solver. In the MRA process, the smoothness of a flow pattern is assessed by the difference between original flow property values, and the values approximated by high‐order interpolating polynomial in decomposition. Insignificant data in smooth region are discarded, and flux computation is performed only where crucial features of a solution exist. The reduction of expensive flow computation improves the overall computational efficiency. In order to maintain the high‐order accuracy, modified thresholding procedure restricts the additional error introduced by the thresholding below the order of accuracy of a conventional solver. The practical applicability of the MRA method is validated in various continuous and discontinuous flow problems. The MRA stably computes the Euler equations for continuous and discontinuous flow problems and maintains the accuracy of a conventional solver. Overall, it substantially enhances the computational efficiency of the conventional third‐order accurate solver. Copyright © 2014 John Wiley & Sons, Ltd.     

A correction for Reynolds-averaged-Navier–Stokes turbulence model under the effect of shock waves in hypersonic flows

Studies on the unphysical increase of turbulent quantities for RANS simulation induced by shock waves in hypersonic flows are carried out. Numerical experiments on the hypersonic flow over a blunt body reveal that the phenomenon of unphysical increase of turbulent quantities across the detached shock wave is induced by the strain-rate-based production terms of the k- and k- SST turbulence models, which leads to the over-prediction of aerothermal prediction. While this phenomenon does not occur for Spalart–Allmaras (S–A) turbulence model because of its vorticity-based production term. In order to eliminate this unphysical phenomenon, and to maintain the accuracy of the original models for boundary layer and separation flows, a new correction method for the k- and k- SST models is proposed: by comparing the orders of magnitude between the strain-rate-based and vorticity-based production terms, the vorticity-based production term is used near the shock waves, while the original strain-rate-based production term is still used in other regions. Finally, the correction method is applied to turbulence and transition flows over blunt bodies, and the numerical results show that the correction method effectively eliminates the unphysical increase of turbulent quantities across shock waves and improves the accuracy of aerothermal and transition onset location prediction.     

Numerical investigation of a water flow in a rib-roughened channel by using Reynolds stress model

In this paper, water flow in a rib-roughened channel is investigated numerically by using Reynolds stress turbulence models (RSM) on a three-dimensional (3-D) domain. Computational results for mean streamwise velocity component and turbulent kinetic energy show good agreements with available experimental data. Five rib pitch-to-height ratios (p/h) of 1, 5, 10, 15 and 20 are analysed for six different Reynolds numbers (Re) of 3000, 7000, 12,000, 20,000, 40,000 and 65,000. Velocity vectors, streamlines and Reynolds stresses are showed for these ratios and Re numbers. Streamlines revealed that Reynolds numbers do not affect flowfield but play an important role in the Reynolds stresses.     

NUMERICAL SIMULATION OF SWIRLING FLOWS IN OXIDATION REACTORS FOR TiO2 MANUFACTURE

The oxidation reactor plays a key role in producing rutile titanium dioxide （TiO2） from vapor-phase titanium tetrachloride （TiCl4） by employing a swirling flow operation for enhanced gas mixing. This work aims to understand the effect of reactor configuration on the 3-D swirling flow field using computational fluid dynamics （CFD） simulation. Considering the anisotropic turbulence involved, the Reynolds stress model is applied to describe the complex swirling flow together with the cross-flow mixing of gases. The results show significant effect of the flow angle between the wall jet of air stream （representing TiCl4 in practice） and the axial direction on the initial flow field of cross-flow mixing, where 60° gives smooth profiles of axial velocity development while 90° may provide the fastest mixing between the jet and the axial bulk flow. The pipe shape for the reaction and developing zone, i.e., straight, expanding and shrinking, shows slight influence on the hydrodynamics.     

On series solution for generalized Falkner–Skan flow of a FENE‐P model

This paper deals with the viscoelastic boundary layer flow past a plate. Constitutive assumptions of the FENE‐P model are taken into account. The pressure gradient is taken as non‐zero. The series solution of the non‐linear problem modelled in (Appl. Math. Lett. 2007; 20 :1211–1215) is developed by a homotopy analysis method (HAM). Numerical solution of the skin friction coefficient is also computed. Further a comparison between the numerical and HAM solutions is provided. Copyright © 2008 John Wiley & Sons, Ltd.