高层住宅厨房主支式集中排风系统的运行特性

目的 为探讨导致集中式排风系统排风量不足甚至出现倒烟的原因及确定最佳管道横截面积.方法 通过CFD方法模拟,建立层数为15层的仿真模型,分别计算了排风管道系统在几个不同规格截面积和设定不同的开机率条件下的典型气体流动工况.并且对照实验装置进行的实际测量数据,对模拟结果进行比较和修正.通过观察系统内压强和速度的分布,分析其排风效果.结果 400 mm×700 mm的管道截面积基本可以满足系统在各开机率下运行,其中30%开机率时,未开机用户全部无回流.而400 mm×500 mm、400 mm×600 mm两种截面积时,各工况下都有不同程度的回流.结论 主管道的截面积和开机率是影响系统排风效果的主要因素.     

气流式水平姿态传感器的三维建模及计算

利用ANSYS-FLOTRAN CFD软件,采用有限元方法,通过建立气流式水平姿态传感器敏感元件的三维实体模型、划分网格、加载和求解等途径,进行了有限元仿真,计算了敏感元件内部的流场,并采用了按实际尺寸比例大小建立整体模型的方法。结果表明：三维实体建模与二位平面建模相比较,这种全尺寸的三维实体建模方法可以使得计算结果更加全面准确,为气流式水平姿态传感器的实用化研究提供更加可靠完备的理论依据。     

高大平房仓U型通风道的优化设计

针对常用的普通U型通风道采用CFD技术,对高大平房仓的机械通风降温过程进行了优化设计,并进行了动态数值仿真.研究表明:改进后的小u型通风道采用反对称的结构设计,充分考虑了粮仓的实际温度场特征,改善了通风均匀性,消除了通风死区,有利于降低能量损失.     

复合材料船用螺旋桨设计与CFD/FEM计算

将基于RANS方程的计算流体力学方法与有限元方法相结合,沿着螺旋桨水动力性能计算、复合材料螺旋桨建模及结构铺层设计、CFD/FEM载荷传递、复合材料螺旋桨结构力学性能计算,水动力性能收敛判定的设计分析流程,完成了某种螺旋桨桨叶的初步的设计过程.提出一种预变形策略以改进复合材料螺旋桨的综合性能.计算结果表明,该复合材料螺旋桨能够满足预定设计指标的要求,在达到传统金属螺旋桨水动力性能要求的同时,减重30%,运行效率增加.研究结果充分说明了所采用设计方法的可行性.     

汽轮发电机冷却风扇的数值模拟及优化

为了深入研究汽轮发电机冷却风扇内的流动规律,并对其设计提出合理优化方案,对某汽轮发电机轴流式通风冷却风扇的原始模型在流量为25m3/s的工况下进行了CFD流场数值模拟,通过改变叶片安放角和叶片扭转角,得到冷却风扇计算效率和叶片安放角及叶片扭转角之间的关系.计算结果表明:在一定范围内,风扇效率和叶片安放角及叶片扭转角之间都呈近抛物线变化关系,在特定叶片安放角和叶片扭转角附近风扇效率最高.经叶片修型后的轴流风扇效率较原模型提高了15.8%.     

深圳大运会主体育场罩棚风压分布的数值模拟

为了求得体育场罩棚的风载体型系数,基于Reynolds时均N-S方程和RSM模型对深圳大运动会主体育场罩棚风压分布特性进行了数值模拟.采用有限体积法对控制微分方程进行离散,并采用SIMPLE压力校正算法来实现非线性方程的迭代求解.将数值计算结果与风洞试验结果进行了对比,两者吻合较好,在此基础上,分析了风向角和风攻角对风压分布的影响,探讨了罩棚周围流场的绕流特性,并根据罩棚的结构形式及风压分布特点,给出了最不利风向下罩棚表面的区域平均风压系数以及罩棚设计风荷载的计算方法.结果表明:风向角对风荷载的影响较大,不同风向角下,来流的分离和漩涡脱落作用均有较大的不同.风攻角对罩棚表面风压分布的影响不大,对罩棚局部峰值的影响在15%以内,整体影响在5%以内.     

Modélisation Mathématique de la Décantation de la Boue Rouge

A good performance of the solid‐liquid unit operation is required for the economical exploitation of the Bayer process. A computational fluid dynamics (CFD) model simulating the operation of the last washing stage mud thickener of a large Canadian alumina plant is presented. The parametric study of the impact of changes in four parameters shows that the diameter of flocculated red mud particles, the feed flow rate and the radius of the feed well are critical parameters for the operation of the thickener.     

Computational fluid dynamics (CFD) modeling of spouted bed: Influence of frictional stress, maximum packing limit and coefficient of restitution of particles

Following the previous article [Du, W., Bao, X., Xu, J., Wei, W., 2006. Computational fluid dynamics (CFD) modeling of spouted bed: assessment of drag coefficient correlations. Chemical Engineering Science 61 (5), 1401-1420], this contribution describes the influences of the frictional stress, maximum packing limit and coefficient of restitution of particles on CFD simulation of spouted beds. Using the two-fluid method embedded in the commercial CFD simulation package Fluent 6.1, the spouting hydrodynamics of a cylindrical-conical spouted bed was simulated and verified with the experimental data of He et al. [He, Y.L., Lim, C.J., Grace, J.R., Zhu, J.X., Qin, S.Z., 1994a. Measurements of voidage profiles in spouted beds. Canadian Journal of Chemical Engineering 72 (4), 229-234; He, Y.L., Qin, S.Z., Lim, C.J., Grace, J.R., 1994b. Particle velocity profiles and solid flow patterns in spouted beds. Canadian Journal of Chemical Engineering 72(8), 561-568]. The results showed that, for coarse particles, the frictional stress is important only for the annulus computation and has no obvious effects on the hydrodynamics of the solids flow in the spout region. The specification of the maximum packing limit could significantly affect the properties of the pseudo-fluid phase of the particles by changing the radial distribution function. The strong dependence of the pseudo-fluid properties of the particle phase, such as pressure, bulk viscosity and shear viscosity, on the granular temperature accounts for the influence of the coefficient of restitution of particles on CFD modeling. The solids volume fraction at loose packing state is suitable for spouted bed simulations, and a pretest of the coefficient of restitution of particles must be conducted when no experimental datum is available.     

Liquid flow and phase holdup—measurement and CFD modeling for two-and three-phase bubble columns

Bubble columns are an important class of contacting devices in chemical industry and biotechnology. Their simple setup makes them ideal reactors for two- and three-phase operations such as fermentations or heterogeneous catalysis. Still, design and operation of these reactors is subject to widely empirical scale-up strategies. With recent advances in the development of measurement techniques, a more detailed approach to the development of optimized reactors for specific operations should become possible. This report is based on detailed measurements of local dispersed phase holdups in a pilot plant-sized bubble column operated at high superficial gas velocities and solid holdups. It deals with the influence of superficial gas velocity, solid loading and sparger geometry on measured and computed liquid flow velocities and holdup distributions. Liquid velocity measurements have been performed using the electrodiffusion method, modeling calculations have been carried out using the computational fluid dynamics (CFD) code CFX-4.3. Measurement results presented here give an insight into the development of liquid circulation and fluctuating velocity distribution depending on superficial gas velocity, solid loading and sparger geometry. CFD results implementing a multi-fluid model with k-ε turbulence and special momentum exchange terms for direct gas-solid interactions show that, even on standard PC workstations, this kind of computations can deliver qualitatively reasonable agreement with measurements.     

Modelling of a RDC using a combined CFD-population balance approach

In the present study we propose an extension of the Euler/Lagrangian approach for liquid-liquid two phase flows when the volume fraction of the dispersed phase is not small. The continuous phase velocity is obtained by solving the Reynolds-averaged Navier-Stokes equations augmented with the k-ε turbulence model. The motion of the dispersed phase is calculated by solving the equations of motion taking into account inertia, drag and buoyancy forces. The coupling between the phases is described by momentum source terms and the terms that account for turbulence generation by the droplets’ motion. Collision and breakage of the droplets are treated by a single particle Monte-Carlo stochastic simulation method. This method is based on a mass flow formulation and operator splitting technique. For validation of the numerical procedure the droplet size distribution and flow fields in a rotating disc contactor are calculated and compared with the existing experimental results.