基于颗粒湍流和颗粒碰撞相互作用规律的湍流模型的研究

颗粒湍流和颗粒碰撞的相互作用规律是两相流动中的核心问题。用颗粒湍流模型和颗粒碰撞的动力论模型叠加的方法在研究两相湍流流动方面取得了一定的成效,但是还有待改进。本文基于颗粒湍流形成大尺度脉动和颗粒间碰撞引起小尺度脉动的概念,从双流体模型出发,建立了两相流动的双尺度kp-pε两相湍流模型。利用该模型对下行床和突扩室内的气固...     

气固两相流场的湍流颗粒浓度理论模型

本文进行了气固两相流动颗粒湍流扩散现象的理论分析，提出了颗粒湍流扩散系数和气流弥散效应二个颗粒湍流模化新概念，在此基础上建立了气固两相流场湍流颗粒浓度模型。理论模型包括离心力和其它外加力场作用下颗粒运动和浓度分布的计算方法。运用湍流颗粒浓度模型，对直管气固两相流动、受限射流气固两相流动和９０°弯管气固两相流动等三种流动做了数值模拟，计算获得颗粒速度、颗粒浓度等主要流动参数。讨论了湍流颗粒浓度模型的适用性。     

强旋湍流气－固两相流动的颗粒随机轨道法模拟

应用颗粒随机轨道模型，并与一种新的代数Ｒｅｙｎｏｌｄｓ应力模型相结合，对新型煤粉涡旋燃烧炉内强旋湍流气。固两相流动进行了数值模拟。得到了与实验相符合的颗粒相密度分布和质量流分布。计算结果表明，在涡旋燃烧炉内的强旋湍流流场中，外壁附近颗粒浓度最高，颗粒停留时间加长，气－固两相间滑移速度增大。     

强旋湍流气－固两相流动的颗粒随机轨道法模拟

应用颗粒随机轨道模型，并与一种新的代数Ｒｅｙｎｏｌｄｓ应力模型相结合，对新型煤粉涡旋燃烧炉内强旋湍流气。固两相流动进行了数值模拟。得到了与实验相符合的颗粒相密度分布和质量流分布。计算结果表明，在涡旋燃烧炉内的强旋湍流流场中，外壁附近颗粒浓度最高，颗粒停留时间加长，气－固两相间滑移速度增大。     

视密度加权的时平均统一二阶矩两相湍流模型

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。     

复杂气固两相系统的微观结构

流化床中的气固两相流动是一个高度复杂的非线性混沌系统。本文利用激光粒子动态分析仪（ＰＤＡ）得到的循环流化床中颗粒脉动速度信号,采用ＦＦＴ分析了脉动信号的宽频谱特征,在此基础上应用小波法分析了脉动信号的动态特征,得到了颗粒脉动速度的微观结构,指出颗粒脉动速度的非线性特性是流化床具有混沌特性的根源,且在不同的尺度上颗粒脉动速度表现出各向异性的特征。     

稀疏两相湍流的惯性颗粒倾向性弥散

气相采用大涡模拟、颗粒相采用拉格朗日轨道模型的方法对后台阶突扩流、充分发展槽道流和圆湍射流3种典型的稀疏气固两相流动进行了数值模拟,研究了颗粒倾向性弥散的特征和规律. 研究表明颗粒的跟随性和倾向性相联系,颗粒惯性和大涡结构同时决定颗粒的倾向性分布特征. Stokes数量级为1(气相时间参考尺度取为宏观特征时间尺度)左右的颗粒,倾向性分布特征最强烈. 颗粒倾向分布于低涡量(或是低脉动速度)的湍流区域.      

大速差射流预燃室内三维回流两相湍流的数值模拟

本文由多流体两相流模型、气相湍流κ-ε模型和颗粒湍流代数模型出发,成功地模拟了真实形状大速差射流预燃室中三维湍流回流两相流动,得到了这类复杂的气固两相流中不同纵横截面上气相速度场、颗粒速度场及浓度场和两相湍流度场的分布,并且获得了与实验定性一致的合理结果,揭示了预燃室中气固两相流动与混合的主要物理特征,探讨了大速差射流技术稳焰和强化燃烧的两相流动机理。     

90°弯管内气固两相湍流流动的数值研究

利用两相湍流KET模型对90°弯管内气固两相湍流流动进行了数值模拟,得到了弯管内两相流动的一些规律,并提出用颗粒动理学压力来定性表征弯管内磨损严重部位,为管道抗磨损设计提供了一定的理论依据。     

颗粒存在对网栅后气相流动湍流特性的影响

应用 L DV测试技术对方管内网栅后的气固两相流动 ,在颗粒平均粒径 Dp =0 .2 1 mm,颗粒质量浓度为 0 .2 4%、0 .36 % ;Dp =0 .35 mm,颗粒质量浓度为 0 .1 2 %、0 .2 1 %、0 .335 % ;Dp =0 .6 mm,颗粒质量浓度为 0 .1 6 %、0 .2 45 %、0 .34 5 % ;Dp =0 .9mm,颗粒质量浓度为 0 .2 0 5 %、0 .30 %多种工况下进行了测量 ,得出各种工况下气流脉动速度、湍动能沿流动方向的衰减规律 ,通过与纯气流条件下的实验结果比较 ,分析了颗粒浓度及颗粒尺寸对网栅后气相流动湍流特性的影响。根据测量结果 ,提出了一个在有固相颗粒存在时 ,关于湍流模型方程中模型常数 C2的修定方法。     

Gas-particle two-phase turbulent flow in a vertical duct

Two-phase gas-phase turbulent flows at various loadings between the two vertical parallel plates are analyzed. A thermodynamically consistent turbulent two-phase flow model that accounts for the phase fluctuation energy transport and interaction is used. The governing equation of the gas-phase is upgraded to a two-equation low Reynolds number turbulence closure model that can be integrated directly to the wall. A no-slip boundary condition for the gas-phase and slip-boundary condition for the particulate phase are used. The computational model is first applied to dilute gas-particle turbulent flow between two parallel vertical walls. The predicted mean velocity and turbulence intensity profiles are compared with the experimental data of Tsuji et al. (1984) for vertical pipe flows, and good agreement is observed. Examples of additional flow properties such as the phasic fluctuation energy, phasic fluctuation energy production and dissipation, as well as interaction momentum and energy supply terms are also presented and discussed.

Applications to the relatively dense gas-particle turbulent flows in a vertical channel are also studied. The model predictions are compared with the experimental data of Miller & Gidaspow and reasonable agreement is observed. It is shown that flow behavior is strongly affected by the phasic fluctuation energy, and the momentum and energy transfer between the particulate and the fluid constituents.     

Speckle optical measurement of a turbulent scalar field with high fluctuation amplitudes

A turbulent temperature field is produced in the gas flow downstream of a turbulence grid by passing the flow through a plane combustion front at the grid that serves as a flame holder. RMS values of the temperature fluctuations of up to 33 K are generated thereby. Properties of the turbulent scalar are measured with an optical speckle technique. The experimental results are compared with theoretical models described by Rotta (1972) and Driscoll and Kennedy (1985). From this comparison it is evident that, even at these high fluctuation amplitudes, the turbulent temperature field still behaves as a passive scalar.     

Influence of the Trailing Edge of a Cavity on the Flow Fluctuation Intensity

Unsteady supersonic turbulent gas flow over a plane cavity is simulated numerically. The solution is determined by means of the joint integration of the Reynolds equations and the two-parameter turbulence model using the law of the wall. The calculation results obtained for various cavity trailing edge contours are considered. The strong effect of the geometry of the trailing edge on the flow parameter fluctuation intensity is demonstrated. A surface shape which makes it possible considerably to reduce these oscillations is determined.     

Effect of drag force on backward-facing step gas-particle turbulent flows

An improved drag force coefficient of gas-particle interaction based on the traditional Wen’s 1966 model is proposed. In this model, a two-stage continuous function is used to correct the discontinuous switch when porosity less than 0.2. Using this proposed correlation and the Wen’s 1966 model, a gas-particle kinetic energy and particle temperature model is developed to predict the hydrodynamic characteristics in backward-facing step gas-particle two-phase turbulent flows. Numerically results showed that they are in good agreement with experiment measurements and presented model are better due to a improvement of momentum transport between gas and particle phases. Particle dispersions take on the distinctively anisotropic behaviors at every directions and gas phase fluctuation velocity are about twice larger than particle phases. Particle phase has a unique transportation mechanism and completely different from the gas phase due to different density. Furthermore, the correlation values of axial–axial gas-particle are always greater than the radial–radial values at fully flow regions. The gas-particle two-phase interactions will make influence on two-phase turbulent flow behaviors.     

Studies on gas turbulence and particle fluctuation in dense gas-particle flows

Particle fluctuation and gas turbulence in dense gas-particle flows are less studied due to complexity of the phenomena. In the present study, simulations of gas turbulent flows passing over a single particle are carried out first by using RANS modeling with a Reynolds stress equation turbulence model and sufficiently fine grids, and then by using LES. The turbulence enhancement by the particle wake effect is studied under various particle sizes and relative gas velocities, and the turbulence enhancement is found proportional to the particle diameter and the square of velocity. Based on the above results, a turbulence enhancement model for the particle-wake effect is proposed and is incorporated as a sub-model into a comprehensive two-phase flow model, which is then used to simulate dilute gas-particle flows in a horizontal channel. The simulation results show that the predicted gas turbulence by using the present model accounting for the particle wake effect is obviously in better agreement with the experimental results than the prediction given by the model not accounting for the wake effect. Finally, the proposed model is incorporated into another two-phase flow model to simulate dense gasparticle flows in a downer. The results show that the particle wake effect not only enhances the gas turbulence, but also amplifies the particle fluctuation.     

连铸结晶器内部流场及熔渣卷入的数值模拟

针对连铸结晶器内部流场及熔渣卷入过程 ,提出了两方程k -ε湍流模型和充填法数值计算模型 ,并采用硅油 /水模拟体系代替熔渣 /钢液体系 ,进行了模拟试验和数值计算。对充气造成的浸入式水口水流脉动的影响进行分析。计算结果与试验结果符合良好 ,表明本文所采用的数值模拟方法是适用的     

The effect of a single vortex generator jet on the characteristics of a turbulent boundary layer

A flat plate experiment was performed in a water tunnel to determine the effects of a vortex generator jet on the characteristics of a turbulent boundary layer at various wall normal locations. The results show that the characteristic distributions of the turbulent fluctuation quantities are nearly unaffected by the induced vortex structures neither in the steady nor in the dynamic blowing case. The shear layer interaction between the turbulent main flow and the jet flow produces less turbulent fluctuations than it is expected from a turbulent free jet flow. Thus, the mixing process of this flow control strategy is based only on a large-scale momentum transport superimposed by the turbulent fluctuation quantities. This allows a separation of scales for physical interpretation and numerical simulations.     

再入湍流尾迹及其对雷达散射的影响研究

就高超声速再入体尾迹等离子体场而言,为进行其亚密湍流雷达散射截面的理论分析,提出了计算湍流尾迹脉动等离子体场强的理论模型及求解方法,即在研究高超声速尾迹流动特征的基础上,推导、使用包括化学组份浓度脉动强度的k－ε－g湍流模型,用以封闭高超声速粘性尾迹湍流运动时均控制方程组,并用全隐式有限差分法求解,算例小钝锥体的飞行条件为零攻角、M_∞＝21．3,Re_（∞D）＝1．33×10~6;M_∞＝20．5;Re_（∞D）＝3．22×10~5,计算结果得到了合理的参数分布;考虑电磁波在上述等离子体介质中的传播,以单电子多次散射模型─—畸变波Born近似方法,计算了湍流尾迹脉动等离子体雷达散射截面,给出散射能（RCS）在不同极化状态下的分布,分析了散射背景场脉动湍流对电磁波在其中传播的影响．     

An investigation of thermally stratified turbulent channel flow with temperature oscillation on the bottom wall by large eddy simulation

Thermally stratified shear turbulent channel flow with temperature oscillation on the bottom wall of the channel is calculated to investigate the behavior of turbulent flow and heat transfer by use of large eddy simulation (LES) approach coupled with dynamic subgrid-scale (SGS) models. The objective of this study is to deal with the effect of the temperature oscillation on turbulent behavior of thermally stratified turbulent channel flow and to examine the effectiveness of the LES technique for predicting statistically unsteady turbulent flow driven by time-varying buoyancy force. To validate the present calculation, thermally stratified shear turbulent channel flow is computed and compared with available data obtained by direct numerical simulation (DNS), which confirm that the present approach can be used to predict thermally stratified turbulent channel flow satisfactorily. Further, to illustrate the effect of the temperature oscillation with different Richardson numbers and periods of the oscillation on turbulence characteristics, the phase-averaged mean value and fluctuation of the resolved velocities and temperature, and instantaneous velocity fluctuation structures are analyzed.