A computational fluid dynamic study of hawkmoth hovering

Liu, Hao and Ellington, Charles P. and Kawachi, Keiji and Van Den Berg, Coen and Willmott, Alexander P. (1998) A computational fluid dynamic study of hawkmoth hovering. The Journal of Experimental Biology, 201 . pp. 461-477. ISSN 0022-0949

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Full text URL: http://jeb.biologists.org/cgi/reprint/201/4/461.pd...

Abstract

A computational fluid dynamic (CFD) modelling
approach is used to study the unsteady aerodynamics of the
flapping wing of a hovering hawkmoth. We use the
geometry of a Manduca sexta-based robotic wing to define
the shape of a three-dimensional ‘virtual’ wing model and
‘hover’ this wing, mimicking accurately the threedimensional
movements of the wing of a hovering
hawkmoth. Our CFD analysis has established an overall
understanding of the viscous and unsteady flow around the
flapping wing and of the time course of instantaneous force
production, which reveals that hovering flight is dominated
by the unsteady aerodynamics of both the instantaneous
dynamics and also the past history of the wing.
A coherent leading-edge vortex with axial flow was
detected during translational motions of both the up- and
downstrokes. The attached leading-edge vortex causes a
negative pressure region and, hence, is responsible for
enhancing lift production. The axial flow, which is derived
from the spanwise pressure gradient, stabilises the vortex
and gives it a characteristic spiral conical shape.

The leading-edge vortex created during previous
translational motion remains attached during the
rotational motions of pronation and supination. This
vortex, however, is substantially deformed due to coupling
between the translational and rotational motions, develops
into a complex structure, and is eventually shed before the
subsequent translational motion.
Estimation of the forces during one complete flapping
cycle shows that lift is produced mainly during the
downstroke and the latter half of the upstroke, with little
force generated during pronation and supination. The
stroke plane angle that satisfies the horizontal force
balance of hovering is 23.6 °, which shows excellent
agreement with observed angles of approximately 20–25 °.
The time-averaged vertical force is 40 % greater than that
needed to support the weight of the hawkmoth.

Item Type:Article
Additional Information:A computational fluid dynamic (CFD) modelling approach is used to study the unsteady aerodynamics of the flapping wing of a hovering hawkmoth. We use the geometry of a Manduca sexta-based robotic wing to define the shape of a three-dimensional ‘virtual’ wing model and ‘hover’ this wing, mimicking accurately the threedimensional movements of the wing of a hovering hawkmoth. Our CFD analysis has established an overall understanding of the viscous and unsteady flow around the flapping wing and of the time course of instantaneous force production, which reveals that hovering flight is dominated by the unsteady aerodynamics of both the instantaneous dynamics and also the past history of the wing. A coherent leading-edge vortex with axial flow was detected during translational motions of both the up- and downstrokes. The attached leading-edge vortex causes a negative pressure region and, hence, is responsible for enhancing lift production. The axial flow, which is derived from the spanwise pressure gradient, stabilises the vortex and gives it a characteristic spiral conical shape. The leading-edge vortex created during previous translational motion remains attached during the rotational motions of pronation and supination. This vortex, however, is substantially deformed due to coupling between the translational and rotational motions, develops into a complex structure, and is eventually shed before the subsequent translational motion. Estimation of the forces during one complete flapping cycle shows that lift is produced mainly during the downstroke and the latter half of the upstroke, with little force generated during pronation and supination. The stroke plane angle that satisfies the horizontal force balance of hovering is 23.6 °, which shows excellent agreement with observed angles of approximately 20–25 °. The time-averaged vertical force is 40 % greater than that needed to support the weight of the hawkmoth.
Keywords:computational fluid dynamics, leading-edge, CFD, insect flight, hovering, hawkmoth, Manduca sexta
Subjects:C Biological Sciences > C300 Zoology
B Subjects allied to Medicine > B830 Biomechanics, Biomaterials and Prosthetics (non-clinical)
Divisions:College of Social Science > School of Sport and Exercise Science
ID Code:3574
Deposited By: Rosaline Smith
Deposited On:31 Oct 2010 16:37
Last Modified:18 Jul 2011 16:34

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