Blips, Coils, and Pedals: Instabilities of negatively buoyant jets in fluids with stable density stratification

Samuel Schofield, University of Arizona

In biological flow experiments, algae gather in a negatively buoyant plume that breaks apart into round blips as it descends. The question of whether the motion of the individual cells is essential to the formation of the instability was posed. Recent three-dimensional and Hele-Shaw experiments have demonstrated that similar behaviors are found in dense jets descending into stably stratified fluids. These experiments have shown a rich array of dynamics including buckling and overturning, blip formation, shear type instabilities in the entrained conduit and multiple jet interactions. However, the flows are quite complex requiring viscous, buoyancy, convection and stratification effects to be considered together. Direct numerical simulation of the Boussinesq equations with high order spectral element methods allows the detailed aspects of the flows to be captured and understood without resorting to excessive approximations. We show that these behaviors are not tied to cell motions in biological flows, surface tensions effects, or Hele-Shaw cells and can be understood in terms of the parameter regimes being considered. Furthermore, we find a vortex street behavior that may be the pedal breakdown observed in other liquid into liquid jet experiments.

Abstract Author(s): Schofield, S. P. and Restrepo, J. M.