Experimental Study on Unstable LayerAppearing in the Drag Reducing Channel Flow of Viscoelastic Fluid
In this paper, drag reducing flow of dilute surfactant solution in two dimensional channel is 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 10000 to 40000 and concentration of additive CTAC (a kind of cationic surfactants) from 25 to 100 ppm on the flow. One of the findings from this study is the appearance of unstable layer in the drag-reducing flow. A train of inclined fluid lumps with high streamwise velocity component at the fixed y-position is appeared in the instantaneous picture of streamwise velocity fluctuation in the flow with surfactant additive. As the turbulent statistics are calculated at identical y-position, w-rms has local maxima at this position. Surprisingly, the position of unstable layer is almost unchanged for number of PIV vector maps. We accumulated five hundred of maps and calculated distribution of turbulent statistics. The profiles of turbulent statistics have multiple peaks corresponding to the position where the unstable layer exists. Moreover, the unstable layer appears in the range of Reynolds number and additive concentration where the drag reduction appears strongly. But the reason of the appearance of unstable layer is not much clear nowadays.
Non-Newtonian fluid Drag-reduction unstable layer Surfactant
W.G.Gu Akihiro Saito Masaaki Motozawa D.Z.Wang Yasuo Kawaguchi
School of Mechanical Engineering, Shanghai Jiao Tong University, 200240 Department of Mechanical Engineering, Faculty of Science and Technology, Tokyo University of Science
国际会议
西安
英文
397-402
2009-07-11（万方平台首次上网日期，不代表论文的发表时间）