High lift developed by multi-element airfoils can
be limited by flow reversals in the wake of the main
element. Turbulent mixing in the wake controls the
growth of the wake and dictates the extent to which
the wake experiences flow reversal. Consequently,
subtle differences in turbulence models make a
significant difference in the prediction of wake
growth. The AST program, in an effort to improve
predictions of high-lift systems, provided funding for
basic experiments that would provide data for
guiding turbulence model development.
The main objective was to devise an experiment
to study wake flow under conditions of adverse
pressure gradient for the purpose of obtaining data
useful in assessing and improving turbulence models
for high-lift systems. Other objectives included
obtaining laser Doppler velocimeter (LDV) measurements
of velocity and turbulent Reynolds stress in a
wake with reversed flow and studying the sensitivity
of the wake to pressure gradient (flow divergence),
asymmetry, and Reynolds number.
Experiments were performed in the High
Reynolds Channel 1 wind tunnel at Ames. Wake flow
behind a splitter plate was subjected to an adverse
pressure gradient by passing the flow through a
divergent wall test section. Boundary layers on the
wind tunnel walls were prevented from separating
with tangential blowing. High Reynolds number
flows (Re c = 10 million) were achieved by pressurizing
the wind tunnel to 6 atmospheres. Two component
LDV measurements of velocity and Reynolds
stress were obtained for several test cases including
separation. The figure shows the tunnel geometry
with streamlines (derived from the velocity measurements)
superimposed for a case with reversed flow
along the centerline of the wake. Also shown are the
measurements of the -uv turbulent Reynolds stress for
the upper half of the channel. The flow was remarkably
stable and repeatable with good spanwise
uniformity.
Point of Contact: D. Driver
(650) 604-5396
ddriver@mail.arc.nasa.gov
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