Mean flow generation by Görtler vortices in a rotating annulus with librating side wallsстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 7 сентября 2016 г.
Аннотация:Time periodic variation of the rotation rate of an annulus induces in supercritical
regime an unstable Stokes boundary layer over the cylinder side walls, generating
Görtler vortices in a portion of a libration cycle as a discrete event. Numerical results
show that these vortices propagate into the fluid bulk and generate an azimuthal
mean flow. Direct numerical simulations of the fluid flow in an annular container
with librating outer (inner) cylinder side wall and Reynolds-averaged Navier–Stokes
(RANS) equations as diagnostic equations are used to investigate generation mechanism
of the retrograde (prograde) azimuthal mean flow in the bulk. First, we explain,
phenomenologically, how absolute angular momentum of the bulk flow is mixed
and changed due to the propagation of the Görtler vortices, causing a new vortex
of basin size. Then we investigate the RANS equations for intermediate time scale
of the development of the Görtler vortices and for long time scale of the order of
several libration periods. The former exhibits sign selection of the azimuthal mean
flow. Investigating the latter, we predict that the azimuthal mean flow is proportional
to the libration amplitude squared and to the inverse square root of the Ekman
number and libration frequency and then confirms this using the numerical data.
Additionally, presence of an upscale cascade of energy is shown, using the kinetic
energy budget of fluctuating flow.