Far field structure of turbulent shallow mixing layers between parallel streams

Zhengyang Cheng, George Constantinescu

Tuesday 30 june 2015

11:00 - 11:15h at Europe 1 & 2 (level 0)

Themes: (T) Water engineering, (ST) Computational methods

Parallel session: 5E. Engineering - Computational

In the present study, a shallow mixing layer that forms between two parallel streams that are initially separated by a thin splitter plate is investigated using fully resolved three-dimensional time-accurate simulations. The ratio between the bulk velocity of the two streams is equal to 2.3 and the Reynolds number defined with the mean velocity of the two streams and the channel depth is Re=15,500. The mixing layer considered in the present study develops in a long constant-depth open channel with a flat smooth bed. The large channel length used in the numerical simulation (400D, where D is the channel depth) allows studying the spatial evolution of the shallow mixing layer at conditions that are close to the equilibrium regime when the destabilizing effect of the mean shear between the two streams is compensated by the stabilizing effect of the friction acting on the mixing layer eddies at the bed. The streamwise variation of the width of the mixing layer and lateral displacement of the mixing layer centerline predicted by the numerical model are found to be in good agreement with experimental results in the region where the shallow mixing layer did not start its transition toward the equilibrium regime. The paper discusses the changes in the structure of the mixing layer with the distance from the origin based on the streamwise variations of the turbulent kinetic energy and mean flow scalar concentration distributions in several cross-sections and in a plane situated close to the free surface.