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The effects of leading-edge tubercles on dynamic stall

Published online by Cambridge University Press:  20 April 2020

John T. Hrynuk Open the ORCID record for John T. Hrynuk [Opens in a new window]  and
Douglas G. Bohl Open the ORCID record for Douglas G. Bohl [Opens in a new window]
John T. Hrynuk*
Affiliation:
Vehicle Technology Directorate, CCDC-Army Research Lab, Aberdeen Proving Ground, MD 21005, USA
Douglas G. Bohl
Affiliation:
Department of Mechanical and Aeronautical Engineering, Clarkson University, 8 Clarkson Avenue, Potsdam, NY 13699, USA
*
†Email address for correspondence: john.t.hrynuk.civ@mail.mil
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Abstract

The effects of leading-edge tubercles, based on the flippers of humpback whales, on the flow field around an airfoil undergoing large-amplitude dynamic changes in the angle of attack have been studied experimentally. Airfoils were pitched from an initial angle of attack of $0^{\circ }$ to $50^{\circ }$ at constant pitch rates with a chord Reynolds number of 12 000. Velocity and vorticity fields around a standard NACA 0012 airfoil and NACA 0012 modified with leading-edge tubercles were quantified using molecular tagging velocimetry. Vortex dynamics were characterized by tracking the location, core radius and circulation. The resulting velocity fields showed that the dynamics of the formation and separation of the leading-edge vortex were fundamentally different between the straight leading-edge airfoil and the tubercled airfoil. The tubercled airfoil also showed spanwise variation in dynamics of the dynamic stall vortex (DSV) formation. The characteristics of the DSV, specifically the circulation and proximity of the DSV to the airfoil suction surface, are known to have an impact on lift during dynamic pitching. The results showed that the DSV was stronger and remained closer to the airfoil longer for the modified airfoil. The baseline DSV convected away from the airfoil faster than the DSV on the tubercled airfoil once it began to separate from the airfoil. Shear-layer vortices, which form during dynamic stall near the mid-cord region, appeared to affect the convective behaviour of the DSV. The results suggest that the leading-edge tubercles observed on Humpback whale flippers act as passive flow-control mechanisms to control or delay dynamic stall.

JFM classification

Vortex Flows: Vortex dynamics
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 893 , 25 June 2020 , A5
Copyright
© The Author(s), 2020. Published by Cambridge University Press

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