Authors

Citation

Xz. Zhang et al., TURBULENCE-INDUCED RECTIFIED FLOWS IN ROTATING FLUIDS, Journal of Fluid Mechanics, 350, 1997, pp. 97-118

Citations number

33

Language

INGLESE

art.tipo

Article

Journal title

ISSN journal

0022-1120

Volume

350

Year of publication

1997

Pages

97 - 118

Database

ISI

SICI code

0022-1120(1997)350:<97:TRFIRF>2.0.ZU;2-Z

Abstract

Laboratory experiments dealing with Reynolds stress gradients in shear
-free turbulence in homogeneous rotating fluids were conducted to bett
er understand associated physical phenomena. The study was motivated b
y possible applications to the oceanic environment where such Reynolds
stress gradients are ubiquitous (e.g. in the vicinity of the continen
tal shelf break, where turbulence decays away from the boundary). The
turbulence was generated by vertical oscillations of a circular shaft
with O-ring surface roughness elements; the oscillation axis coincided
with the axis of symmetry of the cylindrical test cell. In the absenc
e of background rotation, the turbulence is strong in the immediate vi
cinity of the shaft surface and decays with the radial distance, r. Th
e turbulence in the boundary layer is such that u(r) similar to u(thet
a) similar to w, where u(r), u(theta), w are the radial, azimuthal and
vertical r.m.s. velocity components, respectively. These velocity com
ponents are found to be proportional to S omega, where S and omega are
the stroke and frequency of the shaft oscillations, respectively, i.e
. much the same as for the case of oscillating-grid turbulence, which
has been studied extensively. When background rotation is present, the
steady-state turbulent intensity close to the shaft is similar to tha
t of the non-rotating experiments. Away from the shaft, in the central
portion of the test cell, large-scale motions containing randomly dis
tributed cyclonic and anticyclonic vortices are developed owing to sma
ll local Rossby numbers. In the vicinity of the shaft, a rectified ant
icyclonic flow U-theta is observed. The magnitude of U-theta is found
to be proportional to the characteristic r.m.s. turbulence velocity u,
but independent of the rate of background rotation. Consideration of
the equations of motion shows that mean flows should not be expected i
f background rotation is absent. With rotation, however, the equations
indicate that the turbulent stresses can initiate, further develop an
d then maintain a mean anticyclonic (rectified) flow around the cylind
er; the azimuthal momentum equation is shown to play a critical role i
n the generation of the mean anticyclonic flow.