疏浚工程爬坡管内单分散泥浆输送特性数值模拟

Numerical Simulation of Flow Characteristics of Mono-Dispersed Slurry in a Climbing Pipe of Dredging Engineering

基于颗粒动力学理论的两相流欧拉双流体模型,建立可模拟不同爬坡高度(3. 6～5. 0 m)。不同输送速度(5. 0～6. 8 m/s)及不同泥浆浓度(20%～30%)的等温流动过程的计算流体动力学(Computational Fluid Dynamics,CFD)模型,得出疏浚工程中爬坡管内泥浆水力输送流动及阻力特性。研究表明:泥浆在爬坡管中进行输送时其局部阻力系数随着狄恩数减小及爬坡高度上升而增加,且与爬坡高度间成近似线性关系;输送时弯头处最大速度区域由内侧移至外侧,各截面内的颗粒体积分数在垂直和水平方向均表现出梯度;输送过程中存在二次流现象,且泥浆体积分数变化与二次流涡流规律一致,二次流强度随着流速、爬坡高度及泥浆浓度增加而变强。当浓度增大到一定程度时,重力因素超越二次流影响成为主导作用,使流动恢复为直管中充分发展态。

A CFD(Computational Fluid Dynamics)model of Euler-Euler two-fluid model based on the kinetic theory of granular flow is established to simulate the isothermal flow under the conditions of the pipe climbing height ranging from3.6m to5.0m,the conveying velocitie from5.0m/s to6.8m/s,the slurry concentration from20%to30%,and the flow characteristics and resistance characteristics of slurry transport is investigated.The study reveals that the local drag coefficient of slurry transported in the climbing pipe has an approximately linear relation with climbing height,increasing as the Dean number decreases and climbing height increases.The maximum velocity at the elbow moves from the inner side to the outer side when conveying,and the volume fraction of particles at each cross section shows gradient in both vertical and horizontal directions.The secondary flow phenomenon exists in the transportation;the change of slurry volume fraction follows the eddy current law of secondary flow.The secondary flow intensity gets stronger when flow rate/climbing height/slurry concentration increase.When the concentration increases to a certain extent,the gravity factor instead of the secondary flow becomes the dominant factor,so that the flow reverts to a fully developed state,similar to that in a straight pipe.