THE VORTEX SHEDDING OF A STREAMWISE-OSCILLATING SPHERE TRANSLATING THROUGH A LINEARLY STRATIFIED FLUID

Citation
Q. Lin et al., THE VORTEX SHEDDING OF A STREAMWISE-OSCILLATING SPHERE TRANSLATING THROUGH A LINEARLY STRATIFIED FLUID, Physics of fluids, 6(1), 1994, pp. 239-252
Citations number
30
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Mechanics,"Phsycs, Fluid & Plasmas
Journal title
ISSN journal
1070-6631
Volume
6
Issue
1
Year of publication
1994
Pages
239 - 252
Database
ISI
SICI code
1070-6631(1994)6:1<239:TVSOAS>2.0.ZU;2-Y
Abstract
The flow past a horizontally translating, streamwise oscillating spher e through a linearly stratified fluid is investigated in a series of l aboratory experiments. The pertinent governing parameters are shown to be the internal Froude number Fi, the Reynolds number Re, the Keulega n-Carpenter number KC, and the normalized forcing frequency S(f). A KC against S(f) regime diagram for flows at Fi = 0.07 and Re = 190 is de veloped; for these parameters the flow is approximately two dimensiona l in the horizontal zone, -1/2 less than or similar to z/D less than o r similar to 1/2, where z is the vertical coordinate and D is the sphe re diameter. Numerous flow regimes are delineated, and it is shown tha t the regime boundaries approximate the lines of constant u1/u0= 2pi(K C) (S(f)), where u1 is the amplitude of the sphere oscillation and u0 is the magnitude of the mean background flow. Vortex shedding occurs f or the entire range of experiments at these Fi, Re values. Lock-on of the shedding frequency to the sphere oscillation frequency occurs for u1/u0 greater than or similar to 0.1. Flows at large Fi are shown to e xhibit three-dimensional motions in the near wake, and, owing to strat ification, exhibit vertical collapse at a certain distance downstream. The far wake develops into a horizontal vortex street pattern for all flows when stratification is present. At large Fi, Re combinations, t urbulent patches are found in the wake. The inverse normalized streamw ise distance between shed vortices (an effective Strouhal number) is s hown to scale as S(f), independent of KC. Measurements of the horizont al separation angles and times for the collapse of the vertical struct ure are also presented.