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Proceedings Paper

Flow visualization of the effect of pitch amplitude changes on the vortical signatures behind a three-dimensional flapping airfoil
Author(s): Kamalluddien Parker; K. D. von Ellenrieder; J. Soria
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Paper Abstract

The structure of the vortical flow behind a symmetrical airfoil of finite aspect ratio undergoing combinations of heave and pitch motions is investigated using qualitative dye flow visualization. The results are contrasted with flow visualizations obtained using electrolytic precipitation. The effect of changing the pitch amplitude is observed from the plan from view and wingtip view of the airfoil. With a Strouhal number of 0.35, Reyholds number based on airfoil chord of 164 and a phase angle of 90o, the maximum pitch amplitude is varied from 0° to 20°. The geometry of the downstream vortical flow is observed to change suggesting that the induced velocity from interacting structures decreases at lower pitch amplitudes. The rate of dynamic stall development may also be affected by variations in pitch amplitude since it appears that the timing of leading edge separation is affected. The flow field of an airfoil flapping periodically about a fixed axis appears to be influenced by the amplitude of pitching oscillations. At the tested Strouhal numbers the vortex formations appear to be primarily dependent on airfoil oscillation rather than heave translation. Furthermore, the results suggest that the wake structures originating from the dynamic stall process are important for the analysis of these complex flows. While the results from the two flow visualization techniques are similar, the dye flow visualization images provide greater qualitative insight. Inherently, precipitative techniques such as the one used here could provide good flow visualizations since the smoke/particles leave the surface of the airfoil, but the setup is found to be very sensitive to potential changes. The ion content in the electrolytic material was also found to play a role. Furthermore, the high ablation rate of the technique presented some practical problems.

Paper Details

Date Published: 29 April 2003
PDF: 13 pages
Proc. SPIE 5058, Optical Technology and Image Processing for Fluids and Solids Diagnostics 2002, (29 April 2003); doi: 10.1117/12.509776
Show Author Affiliations
Kamalluddien Parker, Monash Univ. (Australia)
K. D. von Ellenrieder, Monash Univ. (Australia)
J. Soria, Monash Univ. (Australia)

Published in SPIE Proceedings Vol. 5058:
Optical Technology and Image Processing for Fluids and Solids Diagnostics 2002
Gong Xin Shen; Soyoung S. Cha; Fu-Pen Chiang; Carolyn R. Mercer, Editor(s)

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