In a cooperative program with Pratt & Whitney, researchers
obtained fundamental separated flow unsteady aerodynamic data
in the NASA Lewis Research Center's Oscillating Cascade. These
data fill a void that has hindered the understanding and prediction
of subsonic and transonic stall flutter. For small-amplitude torsional
oscillations, unsteady pressure distributions were measured on
airfoils with cross sections representative of an advanced, low-aspect-ratio
fan blade. Data were obtained for two mean incidence angles with
a subsonic inflow. At high mean incidence angles (a
= 10°), the mean flow separated at the leading edge and reattached
at about 40 percent of the chord. For comparison purposes, data
were also obtained for a low incidence angle (a
= 0°) attached flow.
The figure shows the effects of incidence angle and reduced frequency
on the chordwise distribution of the unsteady aerodynamic work
per cycle for both the separated and attached flows. Where the
high incidence angle flow was separated (from the leading edge
to about 40 percent of the chord), the unsteady data are dramatically
different. Very near the leading edge, the detached flows have
a strongly destabilizing influence but the attached flows are
strongly stabilizing. At about 15 percent of the chord, the two
sets of curves cross over, with the detached flow becoming stabilizing
and the attached flow becoming destabilizing. Beyond the reattachment
point, differences in the data are much less dramatic.
Buffum, D.H., et al.: Oscillating Cascade Aerodynamics at Large
Mean Incidence. NASA TM-107247, 1996.
Buffum, D.H., et al.: Experimental Investigation of Unsteady Flows
at Large Incidence Angles in a Linear Oscillating Cascade. AIAA
Paper 96-2823 (Also NASA TM-107283), 1996.
Previous articleLast updated April 29, 1997
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