SummaryAn experimental study of the effects on the low-speed
aerodynamic characteristics of a strake-like fillet
is described, modelled on one used on an Airbus A320
variant fitted at the leading edge of a swept
wing-plate junction. The wing, swept back at 20°,
was of NACA 0015 section and chord 500 mm, both
normal to its leading edge. A turbulent boundary
layer had developed on the plate well ahead of the
junction. The tests were conducted at a unit
Reynolds number of 1.56 x 106
m-1.Surface pressure distributions were measured on the
plate in the neighbourhood of the leading edge
junction and also on the aerofoil and fillet at wing
incidences of 0°, 3°, 6°, 9° and 12°. These were
supplemented by surface oil-flow studies.The mean velocity and turbulence intensity fields
around the leading edge were examined for incidences
of 0° and 9°, using both a single tube yaw meter
developed for the purpose and an X-wire anemometer.
The X-wire anemometer was also used downstream of
the trailing edge of the swept wing; five of the
Reynolds stresses and the mean velocity field were
measured.The sectional lift coefficients on the aerofoil were
found to diminish as the junction was approached,
slightly more so with the fillet than without it.
The sectional drag coefficients due to pressure
increased as the junction was approached, the fillet
moderating this increase to only a small extent.However, the addition of the drooped fillet modified
the flow considerably. The horseshoe-like vortex was
less well defined than without it. At zero
incidence, the peak in the turbulence intensity
levels was virtually eliminated on what became
effectively the compression side of the wing due to
the local camber introduced by the asymmetric
fillet. The turbulence levels were also reduced by
the addition of the fillet at an incidence of 9°.
However, the turbulent activity was spread through a
larger proportion of the viscous region. The
secondary flows and the turbulence activity in the
wake are associated with unrecoverable kinetic
energy and will be manifest as drag on the surfaces
forming the junction.It is concluded that a carefully designed fillet,
optimised for the cruise incidence of an aircraft,
can reduce the peak turbulence levels in the
junction. It remains unclear whether the total drag
associated with the junction flow can be reduced
significantly.However because of its effects on the turbulence, there
may be other benefits, for example on the efficiency
of downstream elements, such as fuselage-mounted
engine intakes or the following stages of an axial
flow machine. Junction fillets might also be used to
control the scouring of river beds around bridge
piers.