Prandtl Number Dependence of the Stability of a Stratified Free Shear Layer

A fundamental result of linear inviscid theory for stratified parallel shear flow guarantees stability when the local Richardson number exceeds 0.25 throughout the flow. By extending a numerical study by Maslowe and Thompson, the authors have demonstrated instability for a viscous shear layer at low Prandtl number even with the Richardson number greater than 0.25.