Purging of a Neutrally Buoyant or a Dense Miscible Contaminant from a Rectangular Cavity. I: Case of an Incoming Laminar Boundary Layer
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Volume 133, Issue 4
Abstract
The flow past two-dimensional (2D) channel cavities along with the removal of neutrally buoyant or dense miscible contaminants introduced instantaneously inside the cavity are studied using eddy resolving techniques. In the simulations, the incoming boundary layer is laminar and the flow is observed not to transition to turbulence as it is convected over the cavity. As for these flow conditions the main coherent structures in the separated shear layer over the cavity are quasi-dimensional, 2D simulations are performed. 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 case the contaminant is purged from the cavity mostly due to the interactions between the vortices shed in the separated shear layer with the main recirculation eddies inside the cavity and with the trailing edge corner. In the simulations in which a dense contaminant is introduced inside the cavity, after the initial stages of the mass exchange process, the main phenomenon is the presence of a large amplitude internal wave motion which interacts with a strong cavity vortex situated near the trailing edge corner in between the shear layer and the density interface. The density variation across this oscillatory interface is strong. Through this interaction wisps of denser contaminant are extracted from the region beneath the density interface, before being ejected from the cavity by the separated shear layer vortices. The values of the global mass exchange coefficients for the different phases of the purging process are estimated from simple dead-zone models. As expected, the purging process is delayed in the case in which the density of the contaminant is larger than the one of the carrying fluid.
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Acknowledgments
The first writer was supported by a BK-21 fellowship awarded by KAIST to work on this study during his stay at IIHR Hydroscience and Engineering at the University of Iowa. The writers would also like to thank the National Center for High Performance Computing (NCHC) in Taiwan for providing the computational resources needed to perform some of the simulations.
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Information
Published In
Journal of Hydraulic Engineering
Volume 133 • Issue 4 • April 2007
Pages: 361 - 372
Copyright
© 2007 ASCE.
History
Received: Aug 8, 2005
Accepted: Aug 2, 2006
Published online: Apr 1, 2007
Published in print: Apr 2007
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