EVOLUTION OF MATERIAL LINE IN TURBULENT CHANNEL FLOW

The Lagrangian evolution of passive material lines in a turbulent channel flow is studied through direct numerical simulation (DNS). A series of DNS has been performed for the friction Reynolds number of Reτ = 80–395 with vari-ous initial condition of lines. The present study reveals that fine-scale phenomenon, in particular the near-wall coherent structure, makes a significant contribution to the turbulent mixing. The line stretching rate, normalized by the local Kolmogorov time, is less dependent on the height nor the Reynolds number except the one in the wall vicinity. It is shown qualitatively by visualization of a cross-sectional flow that a streamwise vortex and a bursting process cause the intensive stretching and the anisotropy of the line deforma-tion.