Turbulent diffusion near a free surface

Shen, L; Triantafyllou, GS; Yue, DKP

dc.contributor.author	Shen, L	en
dc.contributor.author	Triantafyllou, GS	en
dc.contributor.author	Yue, DKP	en
dc.date.accessioned	2014-03-01T01:50:32Z
dc.date.available	2014-03-01T01:50:32Z
dc.date.issued	2000	en
dc.identifier.issn	0022-1120	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/26046
dc.subject.classification	Mechanics	en
dc.subject.classification	Physics, Fluids & Plasmas	en
dc.subject.other	OPEN-CHANNEL FLOW	en
dc.subject.other	LARGE-EDDY SIMULATIONS	en
dc.subject.other	SCALE MODELS	en
dc.title	Turbulent diffusion near a free surface	en
heal.type	journalArticle	en
heal.language	English	en
heal.publicationDate	2000	en
heal.abstract	We study numerically and analytically the turbulent diffusion characteristics in a low-Froude-number turbulent shear flow beneath a free surface. In the numerical study, the Navier-Stokes equations are solved directly subject to viscous boundary conditions at the free surface. From an ensemble of such simulations, we find that a boundary layer develops at the free surface characterized by a fast reduction in the value of the eddy viscosity. As the free surface is approached, the magnitude of the mean shear initially increases over the boundary (outer) layer, reaches a maximum and then drops to zero inside a much thinner inner layer. To understand and model this behaviour, we derive an analytical similarity solution for the mean flow. This solution predicts well the shape and the time-scaling behaviour of the mean flow obtained in the direct simulations. The theoretical solution is then used to derive scaling relations for the thickness of the inner and outer layers. Based on this similarity solution, we propose a free-surface function model for large-eddy simulations of free-surface turbulence. This new model correctly accounts for the variations of the Smagorinsky coefficient over the free-surface boundary layer and is validated in both a priori and a posteriori tests.	en
heal.publisher	CAMBRIDGE UNIV PRESS	en
heal.journalName	JOURNAL OF FLUID MECHANICS	en
dc.identifier.isi	ISI:000086674600007	en
dc.identifier.volume	407	en
dc.identifier.spage	145	en
dc.identifier.epage	166	en