Fluid Mixing in Stratified Gravity Currents: The Prandtl Mixing Length

P Odier (1) , J Chen (2) , R.E. Ecke (3)

1 Phys-ENS - Laboratoire de Physique de l'ENS Lyon
2 Purdue University [West Lafayette]
3 Center for NonLinear Studies (CNLS)

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 Rig ≈ 0.08 and Re λ ≈ 100, the mixing lengths are fairly constant, about the same magnitude, comparable to the turbulent shear length.

Domaines: Dynamique des Fluides [physics.flu-dyn]

P Odier, J Chen, R.E. Ecke. Fluid Mixing in Stratified Gravity Currents: The Prandtl Mixing Length. Physical Review Letters, 2009, pp.134504. ⟨10.1103/PhysRevLett.102.134504⟩. ⟨hal-01141224⟩