Abstract
We study numerically and analytically the mixing of a passive scalar in turbulent shear flow with a free surface. The Navier-Stokes and scalar mixing equations are solved by direct numerical simulation. We find that the mean concentration of the scalar exhibits a two-layer structure near the free surface: an outer layer, characterized by a fast reduction in the value of the turbulent diffusivity of the scalar, and a much thinner layer characterized by a fast reduction of the mean concentration gradient. We develop a similarity theory for the variation of the mean concentration, which agrees very well with the numerical results and provides us with scaling relations for the thickness of each layer.
| Original language | English (US) |
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| Pages (from-to) | 913-926 |
| Number of pages | 14 |
| Journal | Physics of Fluids |
| Volume | 13 |
| Issue number | 4 |
| DOIs | |
| State | Published - Jan 1 2001 |