Turbulent Entrainment in Buoyancy Driven Flows in a Stratified Environment using WRF-LES.

Entrainment is an important phenomenon in a wide variety of geophysical fluid flows (density currents, pyroclastic flows, wildland fire plumes).  Ordinarily it is difficult to quantify and measure this.  We use WRF-LES to simulate two-way interactions between the plume and the atmospheric boundary layer (ABL), which has been used to simulate denser and lighter gas plumes into the convectively stratified atmospheric boundary layer by varying initial heat-flux conditions for different gases. In this presentation we examine the unsteady nature of entrainment and its relation to initial source conditions such as reduced gravity terms (g'_T and g'_ρ ) and their relationship to entrainment and further plume development for characteristics such as the plume-(height/width). We further show good agreement with powerlaw relation in the literature. Finally, we present dimensionless parameters to represent this unsteady component of entrainment with the Reynolds and Froude's numbers.