The structure of some variable-density shear flows

The following discussion focuses on the influence of density contrasts on the development of basic shear flows. It is expected, as usual, that what is learnt from these prototype flows can be transposed, at least locally, to more complex geometries. The specific features of these variable-density flows are best accounted for as seen from their vorticity dynamics. The baroclinic torque, connecting misaligned pressure and density gradients, reorganizes the vorticity field according to the fluid inertia. It gives rise to thinner vorticity patches thus shifting enstrophy toward higher wave numbers. It also changes the stability characteristics and the transition to turbulence of laminar shear flows. While frequently commented in geophysical flows under the Boussinesq approximation, it nonetheless deserves a particular attention in the context of inertia-dominated flows encountered in high Reynolds number mixing situations. The baroclinic torque is introduced after a short literature survey. Then the particular cases of the mixing layer and the jet are examined. The two-dimensional and some three-dimensional aspects are documented based on temporally and spatially developing numerical simulations