A fundamental understanding of dynamic-stall onset is important to both rotary- and fixed-wing aerodynamicists. Dynamic stall refers to the stall process of an airfoil executing an unsteady change in angle of attack, for example, sinusoidal pitch oscillations. During such a motion, the airfoil can reach angles of attack exceeding the static-stall angle and generate lift in excess of the maximum static lift. The process culminates in the formation of a dynamic-stall vortex, which propagates along the chord of the airfoil producing large variations in the pitching moment. These pitching-moment variations associated with the dynamic-stall vortex can lead to excessive vibratory loads on aircraft components, such as helicopter pitch links and rotor blades. As a consequence, the large dynamic lift developed prior to the onset of dynamic stall has remained unexploited. A thorough understanding of the mechanism of dynamic-stall vortex formation is necessary for developing a practical control system. Compressible dynamic stall was studied using 148 closely spaced heat-flux gauges distributed over the surface or an oscillating, 15.24-cm chord NACA 0012 airfoil. The study has revealed the various surface flow features of compressible dynamic stall. These include the rapid movement of the transition onset point over the airfoil upper surface on the upstroke with increasing angle of attack, the signature of the convecting dynamic-stall vortex, and the relaminarization of the reattaching shear layer on the downstroke. The imprint of a leading-edge shock has been captured for the first time in the surface flow signature. Even though compressible dynamic stall can originate from several causes depending upon flow conditions, the study led to the conclusion that a deterministic precursor of dynamic-stall onset is a sharp rise in the surface shear stress in the leading-edge adverse pressure gradient region, which is a common and singular flow feature at all conditions tested.
Heat-flux gauge studies of compressible dynamic stall
Untersuchung der Grenzschichtablösung an instationär umströmten Tragflügeln mittels Wärmeflussmessung
AIAA Journal ; 41 , 5 ; 757-762
2003
6 Seiten, 9 Bilder, 12 Quellen
Article (Journal)
English
Heat-Flux Gauge Studies of Compressible Dynamic Stall
AIAA | 2003
|AIRCRAFT TECHNOLOGY, CONVENTIONAL, STOL-VTOL - Heat-Flux Gauge Studies of Compressible Dynamic Stall
Online Contents | 2003
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