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1.
稠密气固两相流各向异性颗粒相矩方法   总被引:1,自引:0,他引:1  
基于气体分子动力学和颗粒动理学方法,考虑颗粒速度脉动各向异性,建立颗粒相二阶矩模型.应用初等输运理论,对三阶关联项进行模化和封闭.考虑颗粒与壁面之间的能量传递和交换,建立颗粒相边界条件模型.采用Koch等计算方法模拟气固脉动速度关联矩.考虑气体-颗粒间相互作用,建立稠密气体-颗粒流动模型.数值模拟提升管内气固两相流动特性,模拟结果表明提升管内颗粒相湍流脉动具有明显的各向异性.预测颗粒速度、浓度和颗粒脉动速度二阶矩与Tartan等实测结果相吻合.模拟结果表明轴向颗粒速度脉动强度约为平均颗粒相脉动强度的1.5倍,轴向颗粒脉动能大约是径向颗粒脉动能3.0倍.  相似文献   

2.
用PDF方程法分析悬沙垂线浓度分布   总被引:6,自引:0,他引:6  
傅旭东  王光谦 《力学学报》2003,35(4):393-400
从颗粒运动的PDF(概率密度分布函数)输运方程出发。建立颗粒相的质量、动量和脉动速度二阶矩方程.对于明渠二维恒定均匀流。利用垂向动量方程导出了新的泥沙扩散方程。表明颗粒脉动强度梯度、升力、重力沉降和紊动扩散都影响悬沙运动。说明了传统扩散方程的不足.理论分析了水沙两相物理属性和水流条件对泥沙扩散系数和浓度分布特征的影响。并通过细颗粒试验资料的分析进行了定量研究.  相似文献   

3.
低浓度固液两相流的颗粒相动理学模型   总被引:11,自引:0,他引:11  
傅旭东  王光谦 《力学学报》2003,35(6):650-659
用广义Fokker-Planck扩散模型描述液相湍动对颗粒的挟带作用,用修正的BGK模型描述粒间碰撞效应,建立了封闭的颗粒相PDF输运方程.运用Chapman-Enskog迭代法求得方程的二阶近似解,获得颗粒相脉动速度二阶矩和三阶矩闭合关系.模型与颗粒流模型相容,与液相湍流闭合模型是否相容依赖于扩散模型的具体形式,并据此比较了不同的涡一颗粒作用模型.模型与二维明渠流轻质沙和天然沙试验资料符合很好.表明细小粒径颗粒能够充分跟随水流运动;大粒径颗粒的相间平均速度差和壁面滑移速度明显,近壁区内的颗粒沿流向和垂向脉动强度都可能大于水流,并存在一定程度的颗粒碰撞效应.  相似文献   

4.
在气粒两相湍流的双流体模型中,颗粒相的视(表观)密度是有脉动的,在时平均的统一二阶矩(USM)模型中出现了和颗粒数密度或视密度脉动有关的项和方程,使模型方程比较复杂。实际上,用LDV或PDPA测量的流体(用小颗粒代表)和颗粒速度都是颗粒数加权平均的结果。因此,在视密度加权平均基础上推导两相湍流模型更为合理。通过推导和封闭了视密度加权平均的统一二阶矩模型(MUSM)方程组,改进了两相速度脉动关联的封闭,并引入了颗粒遇到的气体脉动速度及其输运方程。MUSM模型可以减少所用方程数,节省计算量。视密度加权平均的统一二阶矩两相湍流模型是一种对原有时间平均的统一二阶矩模型和改进和发展。  相似文献   

5.
李婷婷  李青  涂国华  袁先旭  周强 《力学学报》2022,54(6):1523-1532
高超声速飞行器防热材料在气动载荷下发生机械剥蚀,进而影响绕流流态、气动性能、热载荷等,相关颗粒剥离动力学是高超声速热防护系统设计及防热材料体系评价中的共性基础性科学问题.研究通过近壁流动量纲分析,将烧蚀颗粒剥离过程模化为单个圆球惯性烧蚀颗粒在Couette流动中的动力学问题,并采用颗粒解析的直接数值模拟方法开展数值研究,获得了烧蚀颗粒关键特征参量对颗粒输运动力学的影响规律.研究发现,随着颗粒/流体密度比ρr越大,颗粒惯性St越大,则颗粒水平和法向输运速度均减小;随着颗粒粒径d p越大,颗粒惯性St越大,则颗粒水平输运速度减小,但是,法向输运速度和位移均因大颗粒受到更大的Saffman升力而增大.此外,烧蚀颗粒法向位移远小于水平位移,颗粒以水平输运为主.本研究最终建立了颗粒启动速度归一化表达式,发现归一化颗粒启动速度是颗粒和流体惯性的函数,即颗粒水平输运速度等于流体微团或中性浮力颗粒的速度减去惯性修正项.研究结果为烧蚀颗粒调制边界层作用机理研究提供支撑.  相似文献   

6.
考虑颗粒碰撞过程中摩擦作用, 给出了粗糙颗粒碰撞动力学. 引入颗粒相拟总温来表征颗粒平动和转动脉动能量的特征. 基于气体分子运动论, 建立颗粒碰撞中平动和旋转共同作用的粗糙颗粒动理学, 给出了颗粒相压力和黏度等输运参数计算模型. 运用基于颗粒动理学的欧拉-欧拉气固两相流模型, 数值模拟了流化床内气体颗粒两相流动特性, 分析了颗粒旋转流动对颗粒碰撞能量交换和耗散的影响. 模拟得到的流化床内径向颗粒浓度和提升管内颗粒轴向速度与他人实验结果相吻合. 模拟结果表明随着颗粒浓度的增加, 颗粒相压力和能量耗散逐渐增加, 而颗粒拟总温先增加后下降. 随着颗粒粗糙度系数的增加, 床内平均颗粒相拟总温和能量耗散增加, 表明颗粒旋转产生的摩擦将导致颗粒旋转脉动能量的改变, 影响床内气体-颗粒两相宏观流动特性.  相似文献   

7.
FV/MC混合算法求解轴对称钝体后湍流流场   总被引:4,自引:0,他引:4  
介绍一种有限容积/Monte Carlo结合求解湍流流场的相容的混合算法.有限容积法求解Reynolds平均的动量方程和能量方程,Monte Carlo方法求解模化的脉动速度—频率—标量联合的PDF方程.将该算法发展到无结构网格,探讨了在无结构网格中实现两种方法的耦合,包括颗粒定位,颗粒场和平均场之间数据交换等问题.并以二维轴对称钝体后湍流流场作为算例,比较了计算结果与实验结果.  相似文献   

8.
气固两相流中颗粒碰撞的Monte-Carlo数值模拟   总被引:3,自引:1,他引:2  
利用颗粒碰撞动力学模型和颗粒几何碰撞率模型,采用Monte—Carlo算法来模拟颗粒之间碰撞,把该算法与求解雷诺应力-概率密度函数模型的有限差分-Monte Carlo算法耦合起来,对轴对称突扩通道内的两相旋流场进行了数值模拟,模拟结果表明,由于颗粒碰撞使颗粒的动能和湍动能在三个坐标方向上进行了再分配,从而导致颗粒的动能和湍动能在三个坐标方向上趋于各向同性;另外,由于颗粒碰撞破坏了颗粒-颗粒、颗粒-流体微团之间的速度关联,从而造成颗粒湍动能及两相速度脉动关联的降低。  相似文献   

9.
联合二能级气体激光腔中输运方程的简化   总被引:1,自引:0,他引:1  
本文就联合二能级气体激光器(包括流动气体激光器)证明,只要扩散速度之快足以消除空间烧孔,则在输运方程的受激发射和受激吸收项中可应用光强叠加原则,从而导出第一简化方程。进一步利用文献[7]所证明的空间烧孔消除所要求的条件表明,在一般情况下,对连续波激光器均可采用光强叠加原则,本文还进一步给出在第一简化方程中略去扩散项而得到第二简化方程的条件,同时指出,如果采用场强叠加,则不允许略去输运方程中的扩散项。  相似文献   

10.
利用重正化群方法推导湍流二阶矩封闭模型   总被引:2,自引:0,他引:2  
刘正锋  王晓宏 《力学学报》2007,39(2):195-201
Rubinstein和Barton在他们的原始工作中,利用Yakhot-Orszag湍流重正化群方法对雷诺 应力输运方程中的速度-压力梯度项和各向同性回归过程进行了模拟. 文中分析了 其在理论推导过程中存在的数学物理上不自洽的问题及计算错误,并且利用重正化 群方法重新系统地对雷诺应力输运方程进行了模拟,计算得到的湍流常数理论值和 经验值相接近.  相似文献   

11.
The objective of this part of the paper is to summarize the information concerning the authors' works in the field of simulation of two-phase gas-particle turbulent flows with heat transfer and combustion. A kinetic equation had been derived for the probability density function (PDF) of the particle velocity, temperature, and mass distributions in turbulent flows. This PDF equation is used for the construction of the governing conservation equations of mass, momentum, and heat transfer in the dispersed particle phase.The numerical scheme incorporates two-phase fluid dynamics, convective and radiative heat transfer, and combustion. The proposed models have been applied to the calculation of various particle-laden turbulent flows in jets, combustion and gasification chambers, and furnaces.  相似文献   

12.
The purpose of this paper is to present and compare two statistical models for predicting the effect of collisions on particle velocities and stresses in bidisperse turbulent flows. These models start from a kinetic equation for the probability density function (PDF) of the particle velocity distribution in a homogeneous anisotropic turbulent flow. The kinetic equation describes simultaneously particle–turbulence and particle–particle interactions. The paper is focused on deriving the collision terms in the governing equations of the PDF moments. One of the collision models is based on a Grad-like expansion for the PDF of the velocity distributions of two particles. The other model stems from a Grad-like expansion for the joint fluid–particle PDF. The validity of these models is explored by comparing with Lagrangian simulations of particle tracking in uniformly sheared and isotropic turbulent flows generated by LES. Notwithstanding the fact that the fluid turbulence may be isotropic, the particle velocity fluctuations are anisotropic due to the impact of gravitational settling. Comparisons of the model predictions and the numerical simulations show encouraging agreement.  相似文献   

13.
高浓度固-液两相流紊流的动理学模型   总被引:5,自引:0,他引:5  
唐学林  徐宇  吴玉林 《力学学报》2002,34(6):956-962
采用分子动理学方法,基于固-液两相流液相分子或颗粒相颗粒的Boltzmann方程,对Boltzmann方程分别取零矩和一次矩,则得到高浓度固-液两相流紊流的连续方程和动量方程,再和较成熟的低浓度两相流连续方程和动量方程比较,取低浓度两相流控制方程中较成熟合理的有关项和高浓度时由动理学方法推导出的颗粒间碰撞项,则得到高浓度固-液两相流紊流的最终控制方程:连续方程和动量方程.  相似文献   

14.
Two-equation models that treat the transport equations for two variables are typical models for the Reynolds-averaged Navier–Stokes equation. Compared to the equation for the turbulent kinetic energy, the equation for the second variable such as the dissipation rate does not have a theoretical analogue. In this work, the exact transport equation for the eddy diffusivity was derived and examined for better understanding turbulence and improving two-equation models. A new length scale was first introduced, which involves the response function for the scalar fluctuation. It was shown that the eddy diffusivity can be expressed as the correlation between the velocity fluctuation and the new length scale. The transport equations for the eddy diffusivity and the length-scale variance were derived theoretically. Statistics such as terms in the transport equations were evaluated using the direct numerical simulation of turbulent channel flow. It was shown that the streamwise component of the eddy diffusivity is greater than the other two components in the whole region. In the transport equation for the eddy diffusivity, the production term due to the Reynolds stress is a main positive term, whereas the pressure–length-gradient correlation term plays a role of destruction. It is expected that the analysis of the transport equations is helpful in developing better turbulence models.  相似文献   

15.
Fokker-Planck方程有限解析/Monte Carlo数值模拟方法   总被引:4,自引:0,他引:4  
对白噪声驱动随机系统的Fokker-Planck方程进行约化,求得约化方程的解析解,使 用局部解析解和Monte Carlo结合方法求解常系数Fokker-Planck方程,并与常系数Fokker-Planck方程的精确解 进行对比,之后求解了变驱动力系统的行为. 数值模拟结果表明,有限解析/Monte Carlo结合的方法,能成功求解一维Fokker-Planck方程,求解粒子数为10$^{5}$个,能获得 十分光滑的PDF分布曲线,计算颗粒在300个时,就能获得较好的均值. 其研究为两相 湍流PDF模型新计算方法研究提供基础.  相似文献   

16.
The overall objective of this study is to develop a full velocity-scalar filtered mass density function (FMDF) formulation for large eddy simulation (LES) of a separated two-phase flow. Required in the development of the two-phase FMDF transport equation are the local instantaneous equations of motion for a two-phase flow previously derived by Kataoka. In Kataoka’s development, phase interaction terms are cast in terms of a Dirac delta distribution on the phase interface. For this reason, it is difficult to close these coupling terms in the instantaneous formulation and this difficulty is propagated into the phase-coupling terms in the FMDF transport equation. To address this point a new derivation of the local instantaneous equations for a separated two-phase flow is given. The equations are shown to be consistent with the formulation given by Kataoka, and in the development, a direct link between the conditionally surface-filtered coupling terms, arising in the FMDF formulation, and LES phase-coupling terms is established. Clarification of conditions under which conditionally filtered interphase conversion terms in the marginal FMDF transport equations may be disregarded in a separated continuum-dispersed phase flow is discussed. Modeling approaches and solutions procedures to solve the two-phase FMDF transport equation via Monte-Carlo methods are outlined.  相似文献   

17.
This paper presents a review of authors' collective works in the field of two-phase flow modeling done in the past few decades. The paper is aimed at the construction of mathematical models for simulation of particle-laden turbulent flows. A kinetic equation was obtained for the probability density function (PDF) of the particle velocity distribution in turbulent flows. The proposed kinetic equation describes both the interaction of particles with turbulent eddies of the carrier phase and particle-particle collisions. This PDF equation is used for the derivation of different schemes describing turbulent momentum transfer in the dispersed particle phase. The turbulent characteristics of the gaseous phase are calculated on the basis of the k - turbulence model with a modulation effect of particles on the turbulence.

The constructed models have been applied to the calculation of various two-phase gas-particle turbulent flows in jets and channels as well as particle deposition in tubes and separators. For validating the theoretical and numerical results, a wide range of comparisons with experimental data from Russian and foreign sources has been done.  相似文献   


18.
Simple closures for average fluid-particle accelerations, conditional on fixed local fluid velocity, are considered in isotropic, homogeneous and stationary turbulence using exact probability density transport equations and are compared with direct numerical simulations (DNS). Such accelerations are common ingredients in Lagrangian stochastic models for fluid-particle trajectories in turbulence. One-particle accelerations are essentially trivial, so the focus is on two-particle relative accelerations, which are important in the relative dispersion process. The closure is simply a quadratic form in the velocity variable and this special form also defines the Eulerian velocity probability density function (pdf), and comparisons with DNS (for grids up to 5123) of both the acceleration closure and velocity pdf's are encouraging. Received 2 June 1997 and accepted 29 December 1997  相似文献   

19.
Continuum equations for a two-phase fluid-particle flow are developed and applied to the problem of steady, laminar flow over an infinite porous flat plate. Both phases are assumed to behave as non-Newtonian power-law fluids. The effects of particle-particle interaction and diffusion of particles are taken into account in the mathematical model. In addition, the particle phase is assumed to have a non-uniform density distribution. The resulting governing equations are nondimensionalized and solved numerically subject to appropriate boundary conditions using an iterative, implicit finite-difference method. Graphical results for the displacement thicknesses and the skin-friction coefficients for both the fluid and particle phases are presented and discussed to elucidate interesting features of the solutions.  相似文献   

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