Stability of planar buoyant jets in stratified fluids

We consider the flow structure and stability of a planar saline jet descending into a stable, density-stratified fluid. The jet exhibits a rapid acceleration on release, then deceleration, as it encounters the more dense surrounding fluid, yet retains its slender shape due to the low salt diffusion. As the jet descends it entrains fresher water which as it encounters the increasingly dense ambient fluid returns toward the nozzle forming a recirculation zone. Our numerical simulations agree qualitatively with previous experiments and thus serve as a tool to explain the basic kinematics of the jet. We also use numerical means to capture the three instability modes: an antisymmetric instability in the jet core, a symmetric instability in the jet core, and a symmetric instability in the entrained conduit of less saline water. For the dominant antisymmetric instability we determine the range of parameters that demarcate stable and unstable regions. (C) 2010 American Institute of Physics. [doi:10.1063/1.3415493]