Unsteady dynamics of rapid perching manoeuvres
Unsteady dynamics of rapid perching manoeuvres
A perching bird is able to rapidly decelerate while maintaining lift and control, but the underlying aerodynamic mechanism is poorly understood. In this work we perform a study on a simultaneously decelerating and pitching aerofoil section to increase our understanding of the unsteady aerodynamics of perching. We first explore the problem analytically, developing expressions for the added-mass and circulatory forces arising from boundary-layer separation on a flat-plate aerofoil. Next, we study the model problem through a detailed series of experiments at Re = 22 000 and two-dimensional simulations at Re = 2000. Simulated vorticity fields agree with particle image velocimetry measurements, showing the same wake features and vorticity magnitudes. Peak lift and drag forces during rapid perching are measured to be more than 10 times the quasi-steady values. The majority of these forces can be attributed to added-mass energy transfer between the fluid and aerofoil, and to energy lost to the fluid by flow separation at the leading and trailing edges. Thus, despite the large angles of attack and decreasing flow velocity, this simple pitch-up manoeuvre provides a means through which a perching bird can maintain high lift and drag simultaneously while slowing to a controlled stop.
Polet, Delyle T.
28a02cea-943d-4c64-bde4-f096a82b2e79
Rival, David E.
87169441-f569-46d8-8add-bbdbbdc70a01
Weymouth, Gabriel D.
b0c85fda-dfed-44da-8cc4-9e0cc88e2ca0
13 February 2015
Polet, Delyle T.
28a02cea-943d-4c64-bde4-f096a82b2e79
Rival, David E.
87169441-f569-46d8-8add-bbdbbdc70a01
Weymouth, Gabriel D.
b0c85fda-dfed-44da-8cc4-9e0cc88e2ca0
Polet, Delyle T., Rival, David E. and Weymouth, Gabriel D.
(2015)
Unsteady dynamics of rapid perching manoeuvres.
Journal of Fluid Mechanics, 767.
(doi:10.1017/jfm.2015.61).
Abstract
A perching bird is able to rapidly decelerate while maintaining lift and control, but the underlying aerodynamic mechanism is poorly understood. In this work we perform a study on a simultaneously decelerating and pitching aerofoil section to increase our understanding of the unsteady aerodynamics of perching. We first explore the problem analytically, developing expressions for the added-mass and circulatory forces arising from boundary-layer separation on a flat-plate aerofoil. Next, we study the model problem through a detailed series of experiments at Re = 22 000 and two-dimensional simulations at Re = 2000. Simulated vorticity fields agree with particle image velocimetry measurements, showing the same wake features and vorticity magnitudes. Peak lift and drag forces during rapid perching are measured to be more than 10 times the quasi-steady values. The majority of these forces can be attributed to added-mass energy transfer between the fluid and aerofoil, and to energy lost to the fluid by flow separation at the leading and trailing edges. Thus, despite the large angles of attack and decreasing flow velocity, this simple pitch-up manoeuvre provides a means through which a perching bird can maintain high lift and drag simultaneously while slowing to a controlled stop.
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JFMResubmission.pdf
- Accepted Manuscript
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Accepted/In Press date: 24 January 2015
Published date: 13 February 2015
Organisations:
Fluid Structure Interactions Group
Identifiers
Local EPrints ID: 380552
URI: http://eprints.soton.ac.uk/id/eprint/380552
ISSN: 0022-1120
PURE UUID: ca59cf9b-58b6-4c95-a3c1-231998725f40
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Date deposited: 27 Aug 2015 14:45
Last modified: 15 Mar 2024 03:47
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Author:
Delyle T. Polet
Author:
David E. Rival
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