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Variation of leading-edge suction during stall for unsteady aerofoil motions

Published online by Cambridge University Press:  11 August 2020

Shreyas Narsipur Open the ORCID record for Shreyas Narsipur [Opens in a new window] ,
Pranav Hosangadi Open the ORCID record for Pranav Hosangadi [Opens in a new window] ,
Ashok Gopalarathnam Open the ORCID record for Ashok Gopalarathnam [Opens in a new window]  and
Jack R. Edwards
Shreyas Narsipur*
Affiliation:
Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC27695, USA
Pranav Hosangadi
Affiliation:
Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC27695, USA
Ashok Gopalarathnam
Affiliation:
Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC27695, USA
Jack R. Edwards
Affiliation:
Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC27695, USA
*
†Email address for correspondence: shreya@ncsu.edu
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Abstract

The suction force at the leading edge of a round-nosed aerofoil is an important indicator of the state of the flow over the leading edge and, often, the entire aerofoil. The leading-edge suction parameter (LESP) is a non-dimensional version of this force. In recent works, the LESP was calculated with good accuracy for attached flows at low Reynolds numbers (10 000–100 000) from unsteady aerofoil theory. In contrast to this ‘inviscid’ LESP, results from viscous computations and experiments are used here to calculate the ‘viscous’ LESP on aerofoils undergoing pitching motions at low subsonic speeds. The LESP formulation is also updated to account for the net velocity of the aerofoil. Spanning multiple aerofoils, Reynolds numbers and kinematics, the cases include motions in which dynamic stall occurs with or without leading-edge vortex (LEV) formation. Inflections in the surface pressure and skin-friction distributions near the leading edge are shown to be reliable indicators of LEV initiation. Critical LESP, which is the LESP value at LEV initiation, was found to be nearly independent of pivot location, weakly dependent on pitch rate and strongly dependent on Reynolds number. The viscous LESP was seen to drop to near-zero values when the flow is separated at the leading edge, irrespective of LEV formation. This behaviour was shown to correlate well with the loss of streamline curvature at the leading edge due to flow separation. These findings serve to improve our understanding and extend the applicability of the leading-edge suction behaviour gained from earlier works.

JFM classification

Boundary Layers: Boundary layer separation Vortex Flows: Vortex dynamics Vortex Flows: Vortex shedding
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 900 , 10 October 2020 , A25
Copyright
© The Author(s), 2020. Published by Cambridge University Press

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