Direct numerical simulation of vortex structures and turbulent scalar transfer across a free surface in a fully developed turbulence

摘要

Dynamics of well-organized tube-like coherent structures under a free surface and turbulent scalar transfer across the free surface in fully developed turbulent flow in an open channel is investigated. A direct numerical simulation of the three-dimensional Navier-Stokes equations is used to obtain the structure of the free-surface turbulence. First, the effect of the free surface on fully developed turbulence statistics is described. Anisotropy of velocity and vorticity under the free surface are given. Next, the dynamics of the intermittent vortex tubes beneath the free surface are sated. The genesis and development of these coherent structures and their interactions with the free surface are demonstrated. The role of the vortex-surface interactions on the dynamics of turbulence under the free surface, particularly intercomponent energy transfer due to the pressure-strain effect, is discussed. In addition, passive scalar transfer across the free surface is studied. Finally, the promotion of turbulent scalar transfer at the free surface by the vortex/interface interactions is discussed.