The loading on an airfoil during dynamic stall is examined in terms of the augmented lift that occurs and the associated penalties in pitching moment and drag. lt is shown that once stall occurs, and a leading-edge vortex is shed from the airfoil, there is a unique relationship between the augmented lift, the negative pitching moment, and the increase in drag. This relationship shows limited sensitivity to a number of parameters that govern dynamic stall, such as steady and alternating pitch angles and reduced frequency. Second-order polynomials are used to characterize this dynamic stall behavior. lt is shown that the dynamic stall performance of most single-element airfoils is similar, and it appears that little can be done to significantly improve rotorcraft maneuverability except to provide good static Clmax characteristics and the chord or blade number that is required to provide the necessary rotor thrust. The loading on a helicopter blade during a severe maneuver is examined and it is shown that the blade's dynamic stall behavior is similar to that observed in two-dimensional wind tunnel testing. The interaction of the dynamic stall vortex and three-dimensional flow near the blade tip is studied for both a rotor blade in flight and an oscillating wing in a wind tunnel. This comparison shows that there are significant differences in the interaction of the dynamic stall vortex and the tip flow for the two cases. The polynomials used to characterize dynamic stall behavior may be employed as a metric and this is demonstrated by evaluating sample theoretical predictions of semi-empirical stall models and CFD computations. This approach is also shown to be useful in evaluating test data obtained from dynamic stall tests of multi-element airfoils.
Evaluation of airfoil dynamic stall characteristics for maneuverability
Herleitung dynamischer Tragflügelumströmungs-Abrißcharakteristiken zur Verbesserung der Manövrierbarkeit
Journal of the American Helicopter Society ; 46 , 4 ; 239-250
2001
12 Seiten, 22 Bilder, 2 Tabellen, 29 Quellen
Article (Journal)
English
Hubschrauber , Rotor (Drehflügel) , Tragfläche (Aerodynamik) , Abreißen der Strömung , Strömungswiderstand , dynamischer Auftrieb , Wirbelströmung , numerische Simulation , Frequenzbereich , Manövrierfähigkeit , Schubkraft , Strömungsmessung , Windkanal , Theorie-Experiment-Vergleich , Schwingungsanregung , Polynom , CFK (carbonfaserverstärkter Kunststoff)
Evaluation of Airfoil Dynamic Stall Characteristics for Maneuverability
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