MIXING OF A 2-LAYER STRATIFIED FLUID BY A ROTATING-DISK

Citation
Dl. Boyer et al., MIXING OF A 2-LAYER STRATIFIED FLUID BY A ROTATING-DISK, Fluid dynamics research, 21(5), 1997, pp. 381-401
Citations number
17
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Phsycs, Fluid & Plasmas",Mechanics
Journal title
ISSN journal
0169-5983
Volume
21
Issue
5
Year of publication
1997
Pages
381 - 401
Database
ISI
SICI code
0169-5983(1997)21:5<381:MOA2SF>2.0.ZU;2-U
Abstract
An experimental investigation is presented on the large-scale motion h eld and associated mixing of an initially two-layer, equal depth strat ified fluid driven by an impulsively-started, rotating disk at the bas e of the (cylindrical) fluid container. For sufficiently large Reynold s numbers and fixed geometry, the flow is shown to depend on a single parameter, the Richardson number Ri = g'H/(omega R-T)(2), where g' is the reduced gravity, H is the depth of each of the fluid layers, and o mega and R-T are the disk rotation rate and radius, respectively. For Ri <1.5 the primary mixing mechanism is found to be shear-induced bill owing along the primary density interface, with the mixed fluid along this interface being advected into the lower fluid interior by seconda ry motions. An analysis is advanced to show that the elevation of the interface separating the upper (almost quiescent) layer of constant de nsity from the lower mixed region grows as [Ri(-1)(H/R-T)(-1)]omega t, where t is the time. The experimental observations are in good agreem ent with this scaling. The studies reveal that the large-scale seconda ry motion fields characteristic of this physical system force secondar y interfaces, or fronts, to be formed periodically in the lower mixed layer region. These secondary fronts are shown to be relatively weak, with the velocity and density jumps across them being small compared w ith those across the primary interface.