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Unsteady dynamics of rapid perching manoeuvres

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.
0022-1120
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.
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).

Record type: Article

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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More information

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
ORCID for Gabriel D. Weymouth: ORCID iD orcid.org/0000-0001-5080-5016

Catalogue record

Date deposited: 27 Aug 2015 14:45
Last modified: 09 Jan 2022 03:44

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Contributors

Author: Delyle T. Polet
Author: David E. Rival

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