TY - JOUR
T1 - Experimental investigation of polymer diffusion in the drag-reduced turbulent channel flow of inhomogeneous solution
AU - Fu, Zaiguo
AU - Otsuki, Tomohiro
AU - Motozawa, Masaaki
AU - Kurosawa, Taiki
AU - Yu, Bo
AU - Kawaguchi, Yasuo
N1 - Funding Information:
The first author would like to thank the support of the scholarship from Japanese Ministry of Education, Culture, Sports, Science and Technology. Dr. YU Bo also acknowledges the support from the National Natural Science Foundation of China (No. 51325603 ). We also thank Dr. Wang Yi, Mr. Yuichiro Iwaki and Mr. Ryoto Goto for valuable discussions.
PY - 2014/10
Y1 - 2014/10
N2 - Spatial polymer diffusion in the drag-reduced turbulent channel flow of an inhomogeneous polymer solution was investigated by simultaneously measuring velocity and concentration fields using particle imaging velocimetry and planar laser-induced fluorescence techniques. The polymer solution was dosed into the turbulent channel flow from the surface of one-side of the channel wall. The Reynolds number (based on channel height, bulk velocity and solvent viscosity) was set as 4.0 × 104 and the weight concentrations of dosed polymer solution were set to 25, 50 and 100 ppm. The measurements were obtained in the streamwise wall-normal (x-y) plane at three streamwise positions along the dosing wall. The detailed statistical analyses consisting of concentration distribution, turbulence modification, turbulent mass flux, and eddy diffusivities of momentum and of mass are presented. The results show that the polymer diffusion, which has a close relationship with the local polymer concentration and drag reduction in the drag-reduced turbulent channel flow, is suppressed due to the inhibited turbulence other than the diffusion of passive scalar in ordinary turbulence. Two characteristic regions exist in the near-wall region according to the diffusion characteristics and altered motions in the wall-normal direction. The wall-normal turbulent fluxes that control the transport of mass are reduced significantly in the near-wall region for the drag-reduced flow when compared with the case of dosing water. With the increase of local polymer concentration in the "effective position", the corresponding drag reduction rate (DR) increases. The turbulent Schmidt number (ScT), which represents the relative intensities of the eddy diffusivities of momentum and of mass, is also found to increase with increasing DR. The mean value of ScT for the drag-reduced flow can rise to 2.9, while it is 1.2 for the case of dosing water in the present measurements.
AB - Spatial polymer diffusion in the drag-reduced turbulent channel flow of an inhomogeneous polymer solution was investigated by simultaneously measuring velocity and concentration fields using particle imaging velocimetry and planar laser-induced fluorescence techniques. The polymer solution was dosed into the turbulent channel flow from the surface of one-side of the channel wall. The Reynolds number (based on channel height, bulk velocity and solvent viscosity) was set as 4.0 × 104 and the weight concentrations of dosed polymer solution were set to 25, 50 and 100 ppm. The measurements were obtained in the streamwise wall-normal (x-y) plane at three streamwise positions along the dosing wall. The detailed statistical analyses consisting of concentration distribution, turbulence modification, turbulent mass flux, and eddy diffusivities of momentum and of mass are presented. The results show that the polymer diffusion, which has a close relationship with the local polymer concentration and drag reduction in the drag-reduced turbulent channel flow, is suppressed due to the inhibited turbulence other than the diffusion of passive scalar in ordinary turbulence. Two characteristic regions exist in the near-wall region according to the diffusion characteristics and altered motions in the wall-normal direction. The wall-normal turbulent fluxes that control the transport of mass are reduced significantly in the near-wall region for the drag-reduced flow when compared with the case of dosing water. With the increase of local polymer concentration in the "effective position", the corresponding drag reduction rate (DR) increases. The turbulent Schmidt number (ScT), which represents the relative intensities of the eddy diffusivities of momentum and of mass, is also found to increase with increasing DR. The mean value of ScT for the drag-reduced flow can rise to 2.9, while it is 1.2 for the case of dosing water in the present measurements.
KW - Inhomogeneous solution
KW - Planar laser-induced fluorescence
KW - Polymer diffusion
KW - Turbulent Schmidt number
UR - https://www.scopus.com/pages/publications/84903852520
U2 - 10.1016/j.ijheatmasstransfer.2014.06.016
DO - 10.1016/j.ijheatmasstransfer.2014.06.016
M3 - Article
AN - SCOPUS:84903852520
SN - 0017-9310
VL - 77
SP - 860
EP - 873
JO - International Journal of Heat and Mass Transfer
JF - International Journal of Heat and Mass Transfer
ER -