数值摄动算法及其CFD格式

数值摄动算法将流体动力学效应耦合进NS方程组和对流扩散(CD)方程离散的数学基本格式(MBS),特别是耦合进最简单的一阶迎风和二阶中心格式之中,由此构建成一系列新的摄动格式(PS).构建PS的主要步骤是将MBS中的通量重构为步长的幂级数,利用空间分裂和导出的高阶流体动力学线性关系式,并引入下游不影响上游的对流运动规律,通过消除重构格式修正微分方程的截断误差诸项求出幂级数的待定系数,由此获得非线性PS.PS的项是MBS中对应项与R△x(及λR△x)之简单多项式的乘积,R△x和λ分别是网格Reynolds数和网格CFL数.PS和MBS使用相同结点,简单性彼此相当,但PS精度高,稳定范围大,例如PS包含了许多绝对稳定高阶迎风和中心有限差分(FD)格式和绝对正型有限体积(FV)格式,这些格式对网格Reynolds数的任意值均为不振荡格式.数值摄动算法因此是构建高精度不振荡CFD格式的新方法.PS用于计算不可压缩流,可压缩流,液滴萃取传质,微通道两相流等,均获得良好数值结果或与已有Benchmark解一致的数值结果.已有文献称数值摄动算法为新型高精度方法和高算法,文中也讨论了一些值得进一步研究的课题

基于并行CFD方法的颤振特性计算

将流体和结构运动方程分别构造为含子迭代的计算格式,发展一种紧耦合气动弹性分析方法。其中流体计算的空间离散采用改进的HLLEW(Harten-Lax-Van Leer-Einfeldt-Wada)格式,同时采用MPI通信实现并行计算。弹性体网格变形法用于生成随结构变形的四面体非结构网格。利用所发展的方法,对一标模445.6翼型进行了跨声速气动颤振特性研究,分析其颤振特性并对比实验结果。同时还运用所发展的方法对某机带控制舵垂尾的颤振特性进行了研究,确立了所发展方法对实际工程颤振问题的适应性。

CFD analysis of thermodynamic cycles in a pulse tube refrigerator

The objectives of this paper are to study the thermodynamic cycles in an inertance tube pulse tube refrigerator (ITPTR) by means of CFD method The simulation results show that gas parcels working in different parts of ITPTR undergo different thermodynamic cycles The net effects of those thermodynamic cycles are pumping heat from the low temperature part to the high temperature part of the system The simulation results also show that under different frequencies of piston movement the gas parcels working in the same part of the system will undergo the same type of thermodynamic cycles The simulated thermal cycles are compared with those thermodynamic analysis results from a reference Comparisons show that both CFD simulations and theoretical analysis predict the same type of thermal cycles at the same location However only CFD simulation can give the quantitative results while the thermodynamic analysis is still remaining in quality (C) 2010 Elsevier Ltd All rights reserved

Sand storms: CFD analysis of Reynolds stress and collision stress of particles near sand bed

Sand storm is a serious environmental threat to humans. Sand particles are transported by saltation and suspension, causing soil erosion in one place and deposition in another. In order to prevent and predict sand storms, the causes and the manners of particle motions must be studied in detail. In this paper a standard k-epsilon model is used for the gas phase simulation and the discrete element method (DEM) is used to predict the movements of particles using an in-house procedure. The data are summarized in an Eulerian-Eulerian regime after simulation to get the statistical particle Reynolds stress and particle collision stress. The results show that for the current case the Reynolds stress and the air shear stress predominate in the region 20-250 mm above the initial sand bed surface. However, in the region below 3 mm, the collision stress must be taken into account in predicting particle movement. (C) 2010 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

CFD study of a sudden-expanding coal combustor using Euler-Euler and Euler-Lagrange models

In this study, the Euler-Euler (E-E) and Euler-Lagrange (E-L) models designed for the same chemical mechanism of heterogeneous reactions were used to predict the performance of a typical sudden-expanding coal combustor. The results showed that the current E-E model underestimated the coal burnout rate because the particle temperature fluctuation on char combustion is not adequately considered. A comparison of the E-E and E-L simulations showed the underestimation of heterogeneous chemical reaction rates by the E-E model. (C) 2010 Elsevier Ltd. All rights reserved.

CFD-DEM simulation of three-dimensional aeolian sand movement

A three-dimensional CFD-DEM model is proposed to investigate the aeolian sand movement. The results show that the mean particle horizontal velocity can be expressed by a power function of heights. The probability distribution of the impact and lift-off velocities of particles can be described by a log-normal function, and that of the impact and lift-off angles can be expressed by an exponential function. The probability distribution of particle horizontal velocity at different heights can be described as a lognormal function, while the probability distribution of longitudinal and vertical velocity can be described as a normal function. The comparison with previous two-dimensional calculations shows that the variations of mean particle horizontal velocity along the heights in two-dimensional and three-dimensional models are similar. However, the mean particle density of the two-dimensional model is larger than that in reality, which will result in the overestimation of sand transportation rate in the two-dimensional calculation. The study also shows that the predicted probability distributions of particle velocities are in good agreement with the experimental results.

CFD analysis of pneumatic conveying in a double-tube-socket (DTS (R)) pipe

A pipeline with a bypass is widely used for the pneumatic conveying of material. The double-tube-socket (DTS (R)) technology, which uses a special inner bypass, represents the current state of the art. Here, a new methodology is proposed based on the use of computational fluid dynamics (CFD) to predict the energy consumption of DTS conveying. The predicted results are in good agreement with those from pilot-scale experiments. (C) 2010 Elsevier Inc. All rights reserved.

三维风沙运动的CFD-DEM数值模拟

采用计算流体力学(Computational Fluid Dynamics,CFD)和颗粒离散元(Discrete Element Method,DEM)耦合的方法模拟三维风沙运动,并且将三维模拟结果和二维模拟结果以及实验结果进行了对比.计算结果表明:沙粒水平速度随着高度按幂函数规律增加,沙床表面附近沙粒撞击和起跳速度的概率分布均可用对数正态函数描述,沙粒撞击和起跳角度的概率分布均可用指数函数描述,沙粒水平速度,展向速度和垂直速度在不同高度处的概率分布可分别用对数正态分布,正态分布和正态分布表示.与二维计算结果的分析对比表明:二维计算得到的颗粒速度的分布规律和三维计算结果类似,但二维计算的颗粒表观密度明显偏大,由此导致输沙量计算偏大.和实验结果的对比表明:三维计算得到的颗粒速度概率分布与实验基本保持一致