Author:
CHEN A. L.,JACOB J. D.,SAVAŞ Ö.
Abstract
The behaviour of a pair of corotating vortices in the wake of a
flapped airfoil is
experimentally studied in a water towing tank. Reynolds numbers based on
total
circulation of the vortices range from 1.0×104 to
6.4×104. Planar velocity vector
fields and their gradients are derived from PIV images using an adaptive
Lagrangian
parcel tracking algorithm. Isovorticity surfaces are extracted from time
series of
planar vorticity data. The behaviour of the vortices is tracked by using
various
moments of both the probability density distribution and the spatial distribution
of
their streamwise vorticity. All vortices show a Lamb–Oseen circulation
distribution
when they are clearly identifiable. Further, vortices from the apless wing
exhibit
Lamb–Oseen velocity and vorticity distributions with slow growth.
All corotating
vortex pairs are observed to merge at about 0.8 orbit periods. First-order
statistics of
the flow field remain invariant during the merger. The higher-order moments
of the
vorticity distribution show strong time dependence, which implies three-dimensionality
of the flow resulting from vortex stretching. The strengths of the individual
vortices
before merger are constant, and the total circulation before and after
merger remains
constant within the range of observations. The trajectory of the centre
of vorticity
remains unaffected by the merger process. The merger is preceded by a splitting
of
the weaker vortex into filaments which, depending on the relative strengths
of the
vortices, can occur in the radial direction, the axial direction, or a
combination of the
two. Mechanisms contributing to the merger dynamics are discussed.
Publisher
Cambridge University Press (CUP)
Subject
Mechanical Engineering,Mechanics of Materials,Condensed Matter Physics
Cited by
59 articles.
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