The reults of instantaneous velocity measurements on the suction side of a two-dimensional NACA 0015 airfoil pitching at constant angular velocity about its quarter-chord spanwise axis are presented. The experiments were performed in an open-surface water channel at two Reynolds numbers (54000 and 150000) using the technique of particle image velocimetry for the measurement of the instantaneous velocity field. The velocity (and hence vorticity) data obtained in these experiments supplement the surface pressure data obtained in earlier experiments on the same model under the same conditions. The data have been used to obtain quantitative information on the evolution of the flow structure over the pitching airfoil. They have also been compared with results obtained earlier at a low Reynolds number (18000) to examine in some detail the Reynolds number effect on the flow structure. The study has shown that the dynamic-stall vortex (DSV) still consists of the rolled-up shear layer along with remnants of several vortices generated by the shear layer instability, as observed at low Reynolds numbers, and that the increase of lift at post-static stall incidences is still due to the presence of vortical structures close to the surface, till they are eventually ejected prior to the occurence of dynamic stall. Also, the dominant topological features of the flow in the leading-edge region prior to dynamic stall closely resemble the numerical predictions recently reported in the literature for low Reynolds number flows. However, the DSV at high Reynolds numbers is more compact, has fewer remnants of vortical structures, and is ejected abruptly from the airfoil surface in a direction almost normal to the surface. The detailed quantitative experimental data have been archived and are available to any interested user.
Velocity measurements over a pitching airfoil
Strömungsgeschwindigkeitsmessungen über einen angestellten Tragflügel
AIAA Journal ; 35 , 1 ; 119-126
1997
8 Seiten, 8 Bilder, 1 Tabelle, 13 Quellen
Article (Journal)
English
Tragflügel , Anstellwinkel (Tragflügel) , Strömungsgeschwindigkeitsmessung , NACA-Profil , Wasserkanal , Winkelgeschwindigkeit , Saugen , Vergleichsmessung , Reynolds-Zahl , Geschwindigkeitsverteilung , Druckverteilung , Strömungsvorgang , Abreißen der Strömung , Scherströmung , Instabilität , Auftrieb , Topologie , dynamisches Verhalten , optisches Messverfahren , Argonlaser , Photographie (Bild) , Messfehler , Kinematik , Vektor , Wirbelbildung
Velocity Measurements over a Pitching Airfoil
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AIAA | 1997
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