Double-Diffusive Sedimentation

We consider the settling of particles in the presence of a stably stratified temperature or salinity field by means of highly resolved, three-dimensional direct numerical simulations (DNS) of the Navier-Stokes equations. The simulations are conducted by means of a combination of Fourier spectral and sixth order compact finite difference methods. Scenarios are discussed under which double-diffusive and Rayleigh-Taylor instabilities can develop, and we demonstrate the existence of a novel, purely settling-driven instability. Both linear stability analysis and direct numerical simulations are employed in order to elucidate the competition among these instability modes.