THE FLOW GENERATED BY THE ROTATION OF A HORIZONTAL DISK IN A STRATIFIED FLUID

Citation
Pa. Davies et al., THE FLOW GENERATED BY THE ROTATION OF A HORIZONTAL DISK IN A STRATIFIED FLUID, Fluid dynamics research, 17(1), 1995, pp. 27-47
Citations number
NO
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Phsycs, Fluid & Plasmas",Mechanics
Journal title
ISSN journal
0169-5983
Volume
17
Issue
1
Year of publication
1995
Pages
27 - 47
Database
ISI
SICI code
0169-5983(1995)17:1<27:TFGBTR>2.0.ZU;2-4
Abstract
Results are presented from a series of laboratory experiments in which a flow has been generated in a linearly-stratified fluid (initially a t rest in a cylindrical container of radius R(T)) by the impulsive ste ady azimuthal rotation of a flat, smooth, horizontal circular disk of radius R(d). Experiments have been conducted for a range of disk sizes R(d), disk rotation rates omega and buoyancy frequencies N-0, and the spatial and temporal development of the motion and density fields (an d mixing associated therewith) have been shown to be critically depend ent on the ratio R(d)/R(T). For cases in which this ratio is close to unity, the principal mixing mechanisms affecting the flow development are shown to be (i) the localised overturning of fluid forced by the d isk Ekman layers and confining sidewalls and (ii) shear-induced billow entrainment along the outer edge of the so-called primary interface b etween the upper, unmixed fluid and the lower, partially-mixed fluid r egions adjacent to the disk. For the large disk case, for sufficiently high values of omega/N-0, density gradients develop sequentially with time within the partially-mixed region and the forms of the associate d density interfaces also change with time as the primary interface mi grates vertically. At the other extreme, for small values of the ratio R(d)/R(T) but otherwise identical external conditions, the container walls play a negligible role in the flow development and the initial m ixing is achieved primarily by shear-induced billow overturning at the primary interface. A scaling analysis is advanced to predict the grow th rate of the primary interface and the experimental data are shown t o be in good agreement with the analysis.