颗粒动力学与湍动能耦合的稠密两相流动数学模型

在气相湍流流动的k-ε模型基础上,建立了颗粒动力学与湍动能耦合的稠密两相流动数学模型。颗粒相的有效粘性系数取决于颗粒之间相互碰撞而引起的层流粘性以及颗粒微团的湍流脉动而形成的湍流粘性,其中颗粒的碰撞行为以及所形成的颗粒的层流特性用颗粒动力学模型来描述,颗粒的湍流特性采用颗粒湍动能输运方程模型来描述。利用所建立的模型对提升管内气固两相流动过程进行了数值模拟,可以合理地预报出提升管内气固两相的环核流动结构。     

微通道内两相流动的耗散粒子动力学模拟

使用了一种两相的耗散粒子动力学模型来模拟微通道内两相流动相变过程,采用改进了的Verlet速度算法,得到了微通道内流体的速度分布图.DPD粒子流动过程中,粒子出现团聚和稀化的现象,表明流体开始出现汽化.计算结果表明,耗散粒子动力学(DPD)方法可以用于对微通道里的相变过程进行模拟.     

颗粒动力学模型的建立

催化裂化提升管反应器内原料油和催化剂颗粒间存在强烈地传质、传热和动量传递,同时进行着复杂地裂化反应,描述流化状态的催化剂颗粒流动特征非常困难,而它对裂化反应的影响又至关重要,因此人颗粒速度分布函数出发,推导出催化剂颗粒相流动方程结合油气湍流流动、耦合集总动力学模型,得到了催化裂化提升管反应器数学模型,为进步研究提升管内的反应特征和反应历程提供了有力手段。     

双层桨搅拌浸出槽固液两相流场的数值仿真

在石煤提钒搅拌浸出槽的研究中,针对双层桨搅拌浸出槽固液悬浮特性以及混合浸出效果进行了研究.由于实验成本大、操作困难,提出了数值仿真的方法.运用计算流体力学(CFD)软件FLUENT对石煤提钒搅拌浸出槽进行流场仿真,用GAMBIT建立流场实体模型,采用k-ε湍流模型以及多重参考系法(MRF)处理搅拌桨区.探讨了双层桨同向旋转和双层桨异向旋转两种情况下的搅拌效果,结果表明在相同的情况下,双层桨异向旋转时湍动能分布更为合理,并且能够缓解底部沉积,搅拌混合效果更好.仿真结果对于研究搅拌反应容器内部流场规律,进而对搅拌反应容器的结构优化和浸出率的提高具有一定参考价值.     

气液两相圆锥绕流的数值仿真

研究锥形物体在气液两相流场中动特性问题,对流场特性的影响和锥形物体自身的承载受力情况;采用CFD流体仿真软件FLUENT,用欧拉双流体模型结合Realizablek-ε湍流模型,对锥体在气液两相流场中的运动进行数值仿真.结果显示,在锥体尾部形成一组对称的回流涡,随着流体含液率的增加,主相空气相在中心轴线上的流向速度明显受到影响,尾涡变短,恢复速度变快;在绕流体的壁面上的流场的速度梯度会增大;同时绕流体周围的流场的压力梯度也会增大,湍动能和湍动能增量都会增大,与实验的结果基本吻合,验证了运用数值仿真的方法来研究气液两相锥体绕流问题是正确可行的.     

基于多尺度谱熵的气液两相流型动力学特性分析

为了准确分析气液两相流流型的复杂性及其动力学行为,通过计算多尺度谱熵,从频域的角度分析气液两相流在各个尺度下的复杂性及动力学特性。首先分析了几种典型信号的多尺度谱熵特征,并验证了多尺度谱熵算法的可行性以及对噪声的鲁棒性,在此基础上计算了气液两相流泡状流、塞状流及弹状流3种典型流型的多尺度谱熵值,分析了流型频域复杂性演变规律以及相应尺度下的动力学特性。实验结果表明:具有随机性的泡状流的多尺度谱熵最高;而塞状流由于气塞与液塞的交替运动导致多尺度谱熵最低,弹状流的多尺度谱熵居于泡状流和塞状流之间。在第1至第4尺度,3种流型的谱熵变化迅速,且塞状流的谱熵值与弹状流接近,反映出3种流型的微观动力学特性;而在第4尺度后3种流型的谱熵值波动较小,反映出各个流型的宏观特性。因此,多尺度谱熵可定量刻画气液两相流型的频域复杂性,谱熵的变化可以很好的指示流型动力学行为的演变,有助于进一步理解流型演化机理;此外,多尺度谱熵相较传统的时域熵分析方法,计算速度快,计算复杂度低,为两相流流型在线识别及信息的即时处理提供一种新途径。     

基于DSM湍流模型的气固圆湍撞击流模拟

采用改进的DSM大涡模型模拟气相湍流流动,采用颗粒轨道模型模拟颗粒运动,在双向耦合气固湍流数理模型基础上,采用蒙特卡洛方法Tanaka模型进行颗粒碰撞计算,取得相同颗粒数量下不同粒径的固体颗粒随湍射流运动对气相射流的调制规律及颗粒弥散规律.结果 表明,较大粒径的颗粒加强了气流刚性,由于颗粒惯性较大,对冲碰撞使颗粒在碰撞滞止点聚集,使流场中颗粒相浓度分布不均;中等粒径的颗粒对气相耗散较小,颗粒受到离心力主导影响,碰撞后仍沿涡的外围扩散;较小粒径的颗粒对气相耗散严重,颗粒跟随性好,大多聚集在涡核内,碰撞后仍随气体向外扩散,在流场中分布均匀.     

基于热容原理的小管径气液两相流传感器设计

为了识别小管径内气液含量,设计了一种参比铂电阻电极、工作铂电阻电极和加热器复合结构的传感器.基于液体与气体热容率不同,在管道进出口设计了铂电阻电极,采用温度调理电路和温度加热电路实现测量,传感器输出高低电压信号可以区别气液含量.实验结果表明,管径内气体体积小于测量管段体积的50％时,传感器输出低电压信号值0 V;管径内...     

用离散模型模拟多孔介质气固相反应过程的C++实现

多孔介质的气固相反应模拟可分为连续模型和离散模型。离散模型形式简单,不需要求解复杂的偏微分方程组,容易在计算机上实现。但通常离散模型计算量较大,对计算机的运算速度和存储量有一定要求。本文利用C 语言建立了模拟程序,利用C 语言的容器类型变量可以对向量数据进行灵活高效的处理。本文建立了离散网络类,封装了网络构成、网络标注及反应过程总网络变化的算法。该程序能够快速处理多种联接形式的二维或三维网络。利用该模型计算了化学反应控制的多孔介质气固相反应过程的反应速率与转化率的关系,与文献报道的实验结果趋势吻合。     

Numerical simulation of three-dimensional turbulent separated and reattaching flows using a modified turbulence model

A modified version of k-ε model is proposed through modification of the damping function of eddy viscosity that incorporates the effect of wall proximity in the near the wall region and the effect of non-equilibrium away from the wall together with the simple model functions in the ε equation. The proposed turbulence model is validated with the available experimental data of reattachment length, mean streamwise velocity distribution, turbulence intensity profile, and wall static pressure coefficient in the turbulent backward-facing step flows. The predicted results with the present model are in good agreement with the experiments. Computed results reveal that the reattachment length (recirculation zone) and the wall static pressure are decreased with increasing inlet velocity. And the asymmetric distributions of the reattachment point, cross-section view of velocity vector, streamwise skin friction coefficient, and turbulent kinetic energy demonstrate the important three-dimensional side-wall effect in an insufficient aspect ratio channel flow.     

Modeling of heat transfer and turbulent flows inside industrial furnaces

In this work, we present a three-dimensional computational fluid-dynamics model for simulating complex industrial furnaces. The focus in set on the mathematical modeling of heated solids inside the furnace. A stabilized finite element method is used to numerically solve time-dependent, three-dimensional, conjugate heat transfer and turbulent fluid flows. In order to simulate the fluid–solid interaction, we propose the immersed volume method combined with a direct anisotropic mesh adaptation process enhancing the interface representation. The method demonstrates the capability of the model to simulate an unsteady heat transfer flow of natural convection, conduction and radiation in a complex 3D industrial furnace with the presence of six conducting steel solids.     

Adaptive modeling of turbulent flow with residual based turbulent kinetic energy dissipation

In this paper we first review our recent work on a new framework for adaptive turbulence simulation: we model turbulence by weak solutions to the Navier–Stokes equations that are wellposed with respect to mean value output in the form of functionals, and we use an adaptive finite element method to compute approximations with a posteriori error control based on the error in the functional output. We then derive a local energy estimate for a particular finite element method, which we connect to related work on dissipative weak Euler solutions with kinetic energy dissipation due to lack of local smoothness of the weak solutions. The ideas are illustrated by numerical results, where we observe a law of finite dissipation with respect to a decreasing mesh size.     

基于多延时动力系统的交通流量建模

为了改善多车道、路况可变、流量可变的复杂交通环境中关于道路交通流量的问题,采用多时段延时动力系统思想,建立了基于动力系统的道路交通流量新模型．该模型可以描述前后多时间段对道路交通流量的相互影响．仿真数据结果表明,新模型能够模拟真实的交通流量变化,同时对于控制交通流量以及分析交通系统的特点是有效的．     

Numerical simulation of turbulent combustion of subsonic gas jet flows

A physical and mathematical model of turbulent combustion of subsonic gas fuel jet flows flowing into an air space is proposed. The processes are described by averaged equations of the boundary layer with a turbulent viscosity model and a combustion diffusion model. As turbulent viscosity models, the well-known two-parameter k-? standard and k-?? models are taken. The results of the averaged and pulsating flow characteristics?? comparison of numerical calculations with the experimental data are presented.     

A new second-order closure model for rough-wall turbulent flows using the Brinkman equation

A second-order turbulence closure is developed for the new rough-wall layer modeling approach using the Brinkman equation for turbulent flows over rough walls. In the proposed approach, we model the fluid dynamics of the volume averaged flow in the near-wall rough layer by using the Brinkman equation. The porosity can be calculated based on the volumetric characteristics of the roughness and the permeability is modeled. Interface stress jump conditions including the Reynolds stress components are also considered. The Reynolds-averaged Navier-Stokes equations are solved numerically above the near-wall rough layer, while a second-order turbulence closure is employed in all regions. The rough-wall second-order closure is developed by adopting an existing smooth-wall model. The computational results, including the skin friction coefficient, the log-law mean velocity, the roughness function, the Reynolds stresses, and the turbulent kinetic energy, are presented and compared with those obtained by using a previously developed two-equation turbulence closure. The results show that the new rough-wall layer modeling approach with the second-order turbulence closure model satisfactorily predicted the skin friction coefficient, the log-law mean velocity, the roughness function, and the Reynolds shear stress. However, the results for the Reynolds normal stresses are different from the measured data in the inner 20-60% of the boundary layer due to the interface stress jump conditions employed in the present rough-wall layer modeling approach.     

Direct numerical simulation of turbulent channel flows using a stabilized finite element method

Direct numerical simulations (DNS) of incompressible turbulent channel flows at Re_τ = 180 and 395 (i.e., Reynolds number, based on the friction velocity and channel half-width) were performed using a stabilized finite element method (FEM). These simulations have been motivated by the fact that the use of stabilized finite element methods for DNS and LES is fairly recent and thus the question of how accurately these methods capture the wide range of scales in a turbulent flow remains open. To help address this question, we present converged results of turbulent channel flows under statistical equilibrium in terms of mean velocity, mean shear stresses, root mean square velocity fluctuations, autocorrelation coefficients, one-dimensional energy spectra and balances of the transport equation for turbulent kinetic energy. These results are consistent with previously published DNS results based on a pseudo-spectral method, thereby demonstrating the accuracy of the stabilized FEM for turbulence simulations.     

Modeling and animating turbulent gaseous phenomena using spectral synthesis

This paper presents a new spectral synthesis method, motivated by the spectral turbulence theory, for visual modeling and the realistic and computer-effective animation of turbulent gaseous motion in 2-D and 3-D, which avoids the computational costs of direct simulation. Animation of gases is achieved through a phase shift in the frequency domain according to Kolmogorov's exponential law. The parameters of the turbulence model are intuitive, enabling animaters and designers to become familiar with them quickly. Owing to the method's computational effectiveness, an interactive, (quasi-)real-time, parallelized version, which provides the fast feedack needed to easily adjust the model's parameters, could be implemented.