Flow visualization of dynamic stall on an oscillating airfoil

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Author
Brydges, Bruce E.
Date
1989-09Advisor
Chandrasekhara, Muguru S.
Chandrasekhara, M.S.
Second Reader
Platzer, Max F.
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Show full item recordAbstract
Stroboscopic schlieren photography was used to investigate the efFects of
compressibihty, reduced frequency, and amphtude on the dynamic stall of a
NACA 0012 airfoil subjected to sinusoidal oscillation. The Mach number was
varied from M^o = 0.25 to M^o = 0.45 (corresponding to a Reynolds number
variation of Re = 450,000 to Re = 810,000); the reduced frequency was varied
from k = 0.025 to k = 0.10. Oscillation amplitudes of am = 5° and am = 10
were compared. Schlieren photographs are presented, which document the
dynamic stall vortex formation, convection, and shedding sequence for various
experimental conditions. Additionally, a preliminary examination of the flow
reattachment process was conducted. Data derived from the photographs
indicates that increasing the compressibility causes dynamic stall to occur at
lower angles of attack; while, increasing the reduced frequency and/or the
oscillation amplitude effectively delays dynamic stall effects to a higher angle
of attack. Flow reattachment is sensitive to both Mach number and reduced
frequency for low values of these parameters; when either the Mach number
or reduced frequency is sufficiently high, the reattachment process stabilizes.
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