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The effect of aspect ratio on the leading-edge vortex over an insect-like flapping wing.
Bioinspir Biomim. 2015 Oct 09; 10(5):056020.BB

Abstract

Insect 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 (c). 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 6.5c (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 AR > 1.5 around mid-stroke at ~70% span, and initiated sooner over higher aspect ratio wings. At AR > 3 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 AR ~ 5, likely in part due to architectural and physiological constraints but also because of the reducing aerodynamic benefits of high AR wings.

Authors+Show Affiliations

Structure and Motion Laboratory, Royal Veterinary College, University of London, Hatfield, AL9 7TA, UK.No affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article

Language

eng

PubMed ID

26451802

Citation

Phillips, Nathan, et al. "The Effect of Aspect Ratio On the Leading-edge Vortex Over an Insect-like Flapping Wing." Bioinspiration & Biomimetics, vol. 10, no. 5, 2015, p. 056020.
Phillips N, Knowles K, Bomphrey RJ. The effect of aspect ratio on the leading-edge vortex over an insect-like flapping wing. Bioinspir Biomim. 2015;10(5):056020.
Phillips, N., Knowles, K., & Bomphrey, R. J. (2015). The effect of aspect ratio on the leading-edge vortex over an insect-like flapping wing. Bioinspiration & Biomimetics, 10(5), 056020. https://doi.org/10.1088/1748-3190/10/5/056020
Phillips N, Knowles K, Bomphrey RJ. The Effect of Aspect Ratio On the Leading-edge Vortex Over an Insect-like Flapping Wing. Bioinspir Biomim. 2015 Oct 9;10(5):056020. PubMed PMID: 26451802.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - The effect of aspect ratio on the leading-edge vortex over an insect-like flapping wing. AU - Phillips,Nathan, AU - Knowles,Kevin, AU - Bomphrey,Richard J, Y1 - 2015/10/09/ PY - 2015/10/10/entrez PY - 2015/10/10/pubmed PY - 2016/5/24/medline SP - 056020 EP - 056020 JF - Bioinspiration & biomimetics JO - Bioinspir Biomim VL - 10 IS - 5 N2 - Insect 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 (c). 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 6.5c (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 AR > 1.5 around mid-stroke at ~70% span, and initiated sooner over higher aspect ratio wings. At AR > 3 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 AR ~ 5, likely in part due to architectural and physiological constraints but also because of the reducing aerodynamic benefits of high AR wings. SN - 1748-3190 UR - https://www.unboundmedicine.com/medline/citation/26451802/The_effect_of_aspect_ratio_on_the_leading_edge_vortex_over_an_insect_like_flapping_wing_ L2 - https://doi.org/10.1088/1748-3190/10/5/056020 DB - PRIME DP - Unbound Medicine ER -