矩形槽道内表面活性剂减阻流体流场特性

EXPERIMENTAL STUDY ON THE CHARACTERISTICS OF CTAC SOLUTION FLOW IN THE RECTANGULAR CHANNEL

采用粒子图像测速仪对矩形槽道内表面活性减阻流体在流动方向(x方向)与壁面垂直方向(y方向)所在平面的流场进行了测量,分析了速度、涡量、速度脉动相关量在流场内的瞬态分布,以及对500幅相同工况的流场进行了统计平均.结果显示:与牛顿流体相比,表面活性剂减阻流体接近于层流流动,横向速度脉动被大幅减弱,导致湍流输运减弱,雷诺应力远远小于水.减阻流体流向速度脉动呈条带特征,沿流动方向发展,反映了减阻流体不同于水的湍流输运特征.

In the dilute surfactant drag-reducing flow,the slight viscoelasticity of solution affects the energy dissipation process of the flow,and this flow exhibits special fashion different from laminar flow or turbulent one in Newtonian fluid.The study on the modification of turbulent structures by the viscoelasticity of the solution is important to clarify the drag reduction mechanism of surfactant solution flow.In this paper,drag reducing flow of dilute surfactant solution in the two dimensional rectangle channel has been investigated experimentally. To grasp the instantaneous velocity u-v in x-y plane,particle image velocimetry（PIV） is employed.The experiments pay attention to Reynolds number ranging from 10 000 to 40 000 and concentration of additive CTAC（a kind of cationic surfactants） from 25 to 100 ppm on the flow. As for the additive CTAC concentration of 25,40,60 and 100 ppm,the fanning friction factor decreases and drag reduction（DR） increases with the increase of mass concentration below the critical Reynolds number. The surfactant solution with 40 ppm at Re = 40 000,compared with water flow,shows DR of more than 70%. The instantaneous distribution of velocity,vorticity,and correlation of velocity fluctuation is analyzed. Statistics calculation is carried out based on 500 velocity fields which are measured by PIV.The results exhibit that the drag-reducing flow shows the approximate characteristics of the laminar flow.The wall-normal velocity fluctuation of drag-reducing flow is damped,which causes the decrease of turbulence transportation and Reynolds shear stress comparing with the turbulent water flow.The streamwise velocity fluctuation of drag-reducing flow shows the streamwise developed band-like distribution.This pattern indicates the new characteristic of turbulence transportation in drag-reducing flow.