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Unsteady propulsion near a solid boundary

Published online by Cambridge University Press:  21 February 2014

Daniel B. Quinn ,
Keith W. Moored ,
Peter A. Dewey  and
Alexander J. Smits
Daniel B. Quinn*
Affiliation:
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, USA
Keith W. Moored
Affiliation:
Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, PA 18015, USA
Peter A. Dewey
Affiliation:
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, USA
Alexander J. Smits
Affiliation:
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, USA Monash University, Clayton Victoria 3800, Australia
*
†Email address for correspondence: [email protected]
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Abstract

Experimental and computational results are presented on an aerofoil undergoing pitch oscillations in ground effect, that is, close to a solid boundary. The time-averaged thrust is found to increase monotonically as the mean position of the aerofoil approaches the boundary while the propulsive efficiency stays relatively constant, showing that ground effect can enhance thrust at little extra cost for a pitching aerofoil. Vortices shed into the wake form pairs rather than vortex streets, so that in the mean a momentum jet is formed that angles away from the boundary. The time-averaged lift production is found to have two distinct regimes. When the pitching aerofoil is between 0.4 and 1 chord lengths from the ground, the lift force pulls the aerofoil towards the ground. In contrast, for wall proximities between 0.25 and 0.4 chord lengths, the lift force pushes the aerofoil away from the ground. Between these two regimes there is a stable equilibrium point where the time-averaged lift is zero and thrust is enhanced by approximately 40 %.

JFM classification

Aerodynamics: Flow-structure interactions Biological Fluid Dynamics: Propulsion Biological Fluid Dynamics: Swimming/flying
Type
Papers
Information
Journal of Fluid Mechanics , Volume 742 , 10 March 2014 , pp. 152 - 170
Copyright
© 2014 Cambridge University Press 

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