Effect of added vorticity on trailing vortices in the extended near wake
Date
2013-07-23
Authors
Wood, Andrew Robert
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Abstract
Wind Tunnel testing of a rectangular semi-span NACA0012 wing with an actuating
trailing edge flap and two small oscillating tabs, affixed to the model’s wingtip and
flaptip, was undertaken with a view to introduce instabilities in the resulting wake.
The tabs were oscillated sinusoidally at frequencies of 0.5, 1.0, and 2.0 Hz, both
independently and together. The impact on the resulting wake was then studied;
by examining the upper surface pressure distribution over the wing, and through
images captured of the wake cross-section at three positions downstream of the
model. Images were captured by seeding the flow with neutrally buoyant helium
bubbles illuminated under a plane of light. Oscillation of the tabs at all frequencies
was shown to impart instabilities in the near wake. The motion of the resulting
vortex core under the oscillation of the tabs was mapped and shown to behave in
a consistent manner through all angles of attack tested. An oscillation frequency
of 2.0Hz showed the largest evidence of instabilities and greatest wake dispersion of
the frequencies tested. A study into the transient pressure changes at the leading
edge during oscillation of the tabs revealed a pressure oscillation equal to twice the
frequency of the input tab oscillation. It was shown that synchronous oscillation of
the two tabs at a frequency of 2.0 Hz, introduced sufficient instabilities into the flow
to reduce the core diameter and wake extents of the primary wingtip vortex.