Purging of a neutrally buoyant or a dense miscible contaminant from a rectangular cavity. II: Case of an incoming fully turbulent overflow

Abstract

Fully three-dimensional (3D) large-eddy simulation calculations of the flow past two-dimensional cavities for the case in which the incoming flow is fully turbulent are conducted to study the purging of neutrally buoyant or dense miscible contaminants introduced instantaneously inside the cavity. 3D simulations are needed because in the turbulent case (TC), as opposed to the laminar inflow case (LC) considered in the companion paper, the interactions between the coherent structures advected from the incoming channel and the eddies inside the cavity are highly 3D and have a nonnegligible effect on the mass exchange processes between the cavity and channel. Similar to the LC, it is found that the mechanism of removal of the contaminant is very different between the neutrally buoyant and buoyant cases. In the neutrally buoyant TC simulation the contaminant is ejected from the cavity due to the interactions among the large scale eddies in the separated shear layer, the coherent structures convected from the upstream channel over the cavity, and the main recirculation eddies inside the cavity. In the TC simulation with a negatively buoyant contaminant, internal wave breaking is observed to occur over the initial phases of the mixing which, along with other turbulent mixing phenomena, reduces the mean density gradient across the density interface. In the later stages, the contaminant removal and mixing processes are controlled by the interactions of the trailing edge vortex with the bottom layer containing denser contaminant beneath it and upstream of it (for the final stages when the vortex touches the cavity bottom). The oscillations in the size, position, and intensity of the trailing edge vortex are larger than the ones observed in the LC. As expected, turbulent mixing accelerates the purging process in the TC simulations.