Authors

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.