The effect of aspect ratio on the leading-edge vortex over an insect-like flapping wing

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dc.contributor.authorPhillips, Nathan
dc.contributor.authorKnowles, Kevin
dc.contributor.authorBomphrey, Richard J.
dc.date.accessioned2019-11-29T12:47:13Z
dc.date.available2019-11-29T12:47:13Z
dc.date.issued2015-10-12
dc.description.abstractInsect wing shapes are diverse and a renowned source of inspiration for the new generation of autonomous flapping vehicles, yet the aerodynamic consequences of varying geometry is not well understood. One of the most defining and aerodynamically significant measures of wing shape is the aspect ratio, defined as the ratio of wing length (R) to mean wing chord (). We investigated the impact of aspect ratio, AR, on the induced flow field around a flapping wing using a robotic device. Rigid rectangular wings ranging from AR = 1.5 to 7.5 were flapped with insect-like kinematics in air with a constant Reynolds number (Re) of 1400, and a dimensionless stroke amplitude of (number of chords traversed by the wingtip). Pseudo-volumetric, ensemble-averaged, flow fields around the wings were captured using particle image velocimetry at 11 instances throughout simulated downstrokes. Results confirmed the presence of a high-lift, separated flow field with a leading-edge vortex (LEV), and revealed that the conical, primary LEV grows in size and strength with increasing AR. In each case, the LEV had an arch-shaped axis with its outboard end originating from a focus-sink singularity on the wing surface near the tip. LEV detachment was observed for around mid-stroke at span, and initiated sooner over higher aspect ratio wings. At the larger, stronger vortex persisted under the wing surface well into the next half-stroke leading to a reduction in lift. Circulatory lift attributable to the LEV increased with AR up to AR = 6. Higher aspect ratios generated proportionally less lift distally because of LEV breakdown, and also less lift closer to the wing root due to the previous LEV's continuing presence under the wing. In nature, insect wings go no higher than likely in part due to architectural and physiological constraints but also because of the reducing aerodynamic benefits of high AR wings.en_UK
dc.identifier.citationPhillips N, Knowles K, Bomphrey R. (2015) The effect of aspect ratio on the leading-edge vortex over an insect-like flapping wing. Bioinspiration and Biomimetics, Volume 10, Issue 5, October 2015, Article number 056020en_UK
dc.identifier.cris15381448
dc.identifier.issn1748-3182
dc.identifier.urihttps://doi.org/10.1088/1748-3190/10/5/056020
dc.identifier.urihttp://dspace.lib.cranfield.ac.uk/handle/1826/14784
dc.language.isoenen_UK
dc.publisherIOPen_UK
dc.rightsAttribution 3.0 International*
dc.rights.urihttp://creativecommons.org/licenses/by/3.0/*
dc.subjectaspect ratioen_UK
dc.subjectflapping wingen_UK
dc.subjectleading-edge vortexen_UK
dc.subjectmicro air vehicleen_UK
dc.titleThe effect of aspect ratio on the leading-edge vortex over an insect-like flapping wingen_UK
dc.typeArticleen_UK

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