Large eddy simulations of a forced plume subjected to volumetric heating in a stratified medium

We present a computational study of a forced plume subjected to volumetric off-source heating in a stratified medium using large eddy simulations. A detailed validation of the LES code is performed by comparing the mean vertical velocity and the entrainment rate coefficient with the reported experimental results. Two parameters are varied in this study, first is the heating rate represented by heat release number G , and second is the background stratification represented by buoyancy frequency N_∞ . Heating leads to acceleration of the plume due to additional buoyancy. Entrainment is also found to increase at the beginning of the heat injection zone (HIZ) followed by a drastic reduction in the entrainment towards the end of HIZ. Heating is found to increase the vorticity magnitude as well as the TKE above the heating zone, while stratification is observed to counteract the effects of heating by suppressing the turbulence. An increase in the turbulence kinetic energy (TKE) above the heating zone is primarily contributed by the increase in buoyancy production. As the stratification strength increases, the neutral buoyancy height comes down and a significant reduction in the vorticity and TKE is observed above the HIZ. The kinetic energy spectrum reveals a scaling of κ _z^-3 for an unheated plume and κ _z^-11/5 for a heated plume at low wavenumbers. A narrow band of κ _z^-5/3 scaling is observed at higher wavenumbers for both heated and unheated plumes.