共查询到19条相似文献,搜索用时 62 毫秒
1.
2.
3.
4.
5.
挤出胀大的数值模拟是非牛顿流体研究中具有挑战性的问题.本文运用格子Boltzmann方法(LBM)分析Oldroyd-B和多阶松弛谱PTT粘弹流体的挤出胀大现象,采用颜色模型模拟出口处粘弹流体和空气的两相流动,通过重新标色获得两种流体的界面,并最终获得胀大的形状.Navier-Stokes方程和本构方程的求解采用双分布函数模型.将胀大的结果与解析解、实验解和单相自由面LBM结果进行了比较,发现格子Boltzmann两相模型结果与解析解和实验结果相吻合,相比于单相模型,收敛速度更快,解的稳定性更高.研究了流道尺寸对胀大率的影响,并对挤出胀大的内在机理进行了分析. 相似文献
6.
7.
当随机散布细颗粒的流体以低Re数层流流入直管时, 经过一段距离的流动后, 这些颗粒会被稳定地聚集在一个离管道中心固定距离的同心圆环位置上运动. 这种运动特征被称为颗粒“惯性聚集”现象. 该现象表明: 在相应的Re数管流中, 颗粒除受到流体沿主流方向的驱动力同时, 还受到垂直于主流的横向力的作用. 这种横向力是使颗粒产生聚集运动现象的主要原因, 被认为是由于流场的惯性力对颗粒的作用. 相似文献
8.
运用基于欧拉-欧拉方法的混合欧拉多相流模型结合雷诺应力湍流模型,对较大雷诺数下的水平固液两相湍流进行了数值计算,主要考察了以Kolmogorov尺度(约为2v/ur)为临界值的细小沙粒颗粒在5%的固相体积分数下对湍流场的调制及其减阻效应.研究发现,无量纲颗粒直径dp+≤2的小颗粒减小了固液两相湍流的雷诺应力,并且三个方向上的速度脉动也被不同程度地削弱;而dp+=4的大颗粒使缓冲层区域的雷诺应力稍增大,在增强法向速度脉动的同时对流向脉动有抑制作用,并且值得关注的是,较大颗粒的存在导致缓冲层中的部分区域出现了流变现象.在减阻方面,较小的颗粒(dp+≤2)有大致相同的减阻表现,而大颗粒(dp+=4)已经失去了减阻性能,总体上看,在所研究的情形下微颗粒的减阻性能随着其粒径的增大而降低. 相似文献
9.
本文应用格子Boltzmann 方法(LBM)并结合Oldroyd-B 模型,讨论了不可压缩的 Navier-Stokes 方程和平流扩散本构方程的解耦及各自求解方法,以及两类问题的边界处理格式,实现了黏弹性流体在二维1:3 扩展流道以及3:1 收缩流道中的流动的数值模拟.获得了不同雷诺数Re 和维森伯格数Wi 以及黏度vs 下流动的流线分布,计算给出了漩涡的涡心位置和大小,并分析了参数Re、Wi 和vs 对流动特点的影响.模拟结果表明本文所采用模型和边界处理方法具有良好的精度和稳定性. 相似文献
10.
以液固两相流冲洗油管道为研究对象,采用Realizableκ-ε湍流模型、随机轨道模型,结合液固两相流冲蚀磨损试验,建立修正的冲蚀磨损数理模型,数值预测典型工况下冲洗油管道内速度、压力、冲蚀磨损率等流动参数分布情况,分析了冲蚀磨损的形成机制.研究结果表明:受曲率半径影响,冲洗油管道冲蚀磨损速率随曲率半径的增加而减小;由于颗粒惯性及管内二次流影响,弯头中间区域外侧壁面和出口直管段内侧面磨损较为严重,三通管件的最大冲蚀磨损率位于孔口处,数值预测结果与失效解剖案例吻合.本文建立的冲蚀磨损定量预测方法,适用于压力管道的风险评定及寿命预测. 相似文献
11.
本文采用Euler-Lagrange两相流研究方法,固相采用离散相(DPM)模型,对三种不同夹角的Y型分支管内气固两相流动进行了数值模拟.气相湍流采用Realizable k-ε模型,固相的湍流耗散采用随机轨道模型.模拟结果较好地预估了颗粒在分叉处的流动形态、颗粒在分支管内的运动轨迹,以及重新实现颗粒相流场均匀分布所需的距离.同时发现,随机轨道模型较适于评估分支与主管夹角较大情况下,固体颗粒在分叉处的运动.将分支管内固体颗粒质量分配的数值模拟结果与试验结果比较,发现两者较吻合,相对误差较小. 相似文献
12.
圆管流动水击压力波测量及水力计算 总被引:2,自引:0,他引:2
为探索水击现象的物理过程和机理,研制了自循环定常流动管路瞬态特性计算机控制试验装置,并利用该装置进行圆管流动水击压力波实验测量。用12只扩散硅压力传感器测定圆管流动水击压力波瞬态分布及最大、最小压力值,由试验数据拟合出水击波波形,揭示了水击压力波传播方式、特性及衰减规律。通过分析随机捕捉测量技术方法,理论上推断出测量数据达到可信精度。在归纳分析试验数据基础上,得出最大压力随关阀时间的关系曲线,对圆管流动直接水击等概念进行了探讨,用数值分析方法拟合出水击最大压力水力计算修正方程式。 相似文献
13.
14.
Flow and heat transfer characteristics inside a wavy tube 总被引:2,自引:0,他引:2
15.
Turbulent two-phase flow equations are derived and solved for fully developed pipe flow using a composite eddy-viscosity model
and a new void-fraction equation. The void fraction profile is first specified from experiments and the velocity field is
calculated to validate the eddy-viscosity model. Consequently, a new equation is presented for calculation of the void fraction.
This void-fraction equation incorporates the gradient of turbulent normal stresses in the radial direction, the conventional
lift force, and a contribution from the unsteady drag force. The implications of this new equation, for the bubbly flow regime,
are investigated by calculating the void-fraction distribution for a given velocity field. Inclusion of the normal turbulent
stresses in the radial direction is shown to simulate correctly the experimentally observed trends of the phase distribution,
both for upward and downward bubbly flow, without the need for a fictitious term such as the so called ``lubrication force'.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
We present an analytical solution of axisymmetric motion for a Bingham fluid initially at rest subjected to a constant pressure gradient applied suddenly. Using the Laplace transform, we obtain expressions which allow the calculation of the instantaneous velocity, plug radius and rate of flow as a function of time. We also give a relation for the shear stress in the plug and in the region where the behaviour of the fluid is Newtonian. 相似文献
17.
Holger Kocherscheidt Maren Schmidts Venkatesa I. Vasanta Ram 《Flow, Turbulence and Combustion》2002,69(1):79-94
The present paper describes an experiment to study the response of the swirling flow in a pipe at a high Reynolds number to
a rapid temporal change in swirl. The measurements have been conducted with 3D-LDV in a facility of special design that operates
on the principle of refractive-index matching and in which swirl is generated in the flow by a tube-bundle in the pipe rotating
about its own axis. The temporal change in swirl is effected by a computer controlled change of the angular velocity of the
swirl generator. Measurement data from both cases, of increase and decrease of swirl, are presented.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
19.
In this article, the numerical simulations for one-dimensional three-phase flows in fractured porous media are implemented.
The simulation results show that oil displacement in matrix is dominated by oil–water capillary pressure only under certain
conditions. When conditions are changed to decrease the amount of water entering into the fractured media from the boundary
of the flow field, water in fracture may be vaporized to superheated steam. In these cases, the appearance of superheated
steam in fracture rather than in matrix will decrease the fracture pressure and generate the pressure difference between matrix
and fracture, which results in oil flowing from matrix to fracture. Assuming that oil is wetting to steam, the matrix steam–oil
capillary pressure will decrease the matrix oil-phase pressure as the matrix steam saturation increases. After the steam–oil
capillary pressure finally exceeds the pressure difference due to the appearance of superheated steam in fracture, the oil
displacement in matrix will stop. It is also shown that variations of the water relative permeability curve in matrix do not
result in different mechanisms for oil displacement in matrix. The simulation results suggest that the amount of liquid water
supply from the boundary of flow field fundamentally influence the mechanisms for oil displacement in matrix. 相似文献