Interferometric Investigations of Compressible Dynamic Stall Over a Transiently Pitching Airfoil
Abstract
The dynamic stall flow field over a NACA 0012
airfoil pitching transiently from 0 - 60 degrees at a constant
rate under compressible flow conditions has
been studied using the real-time technique of point
diffraction interferometrv. This investigation using
nonintrusive diagnostics-provides a quantitative
description of the overall flow field, including the finer
details of dynamic stall vortex formation, growth and
the concomitant changes in the pressure distribution.
Analysis of several hundred interferograms obtained
for a range of flow conditions shows that the peak
leading edge suction pressure coefficient at stall is
nearly constant for a given free stream Mach number
at all nondimensional pitch rates. Also, this value is
below that seen in steady flow at static stall for the
same Mach number, indicating that dynamic effects
significantly affect the separation behavior. Further,
for a given Mach number, the dynamic stall vortex
seems to form rapidly at nearly the same angle of
attack for all pitch rates studied. As the vortex is
shed, it induces an anti-clockwise trailing edge vortex,
which grows in a manner similar to that of a
starting vortex. The measured peak suction pressure
coefficient drops as the free stream Mach number increases.
For free stream Mach numbers above 0.4,
small multiple shocks appear near the leading edge
above the shear layer. The unsteady flow peak suction
pressure coefficient at any angle has been experimentally
demonstrated to lag that of the steady flow at the same angle of attack.
Description
The article of record as published may be found at http://dx.doi.org/10.2514/6.1993-211
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Interferometric Investigations of Compressible Dynamic Stall Over a Transiently Pitching Airfoil
Chandrasekhara, M.S.; Carr, L.W.; Wilder, M.C. ;The compressible dynamic stall flowfield over a NACA 0012 airfoil transiently pitching from 0 to 60 deg at a constant rate under compressible flow conditions has been studied using real-time interferometry. A quantitati ... -
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