Mixing in stratified gravity currents: Prandtl mixing length

Abstract

Shear-induced vertical mixing in a stratified flow is a key ingredient of thermohaline circulation. We experimentally determine the vertical flux of momentum and density of a forced gravity current using high-resolution velocity and density measurements. A constant eddy viscosity model provides a poor description of the physics of mixing, but a Prandtl mixing length model relating momentum and density fluxes to mean velocity and density gradients works well. For $<R{i}_g>\approx 0.08$ and $R{e}_{\lambda }\approx 100$, the mixing lengths are fairly constant, about the same magnitude, comparable to the turbulent shear length.

4 pages, 4 figures, accepted in PRL, February 2009

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