QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online December 1, 2006
Journal of Experimental Biology 209, 5005-5016 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02614

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lu, Y. Articles by Lai, G. J. Search for Related Content PubMed PubMed Citation Articles by Lu, Y. Articles by Lai, G. J.

Dual leading-edge vortices on flapping wings

Yuan Lu, Gong Xin Shen^* and Guo Jun Lai

Full Flow Field Observation and Measurement, Institute of Fluid Mechanics, Beijing University of Aeronautics and Astronautics, Beijing 100083, People's Republic of China

View larger version (47K): [in this window] [in a new window]   Fig. 1. Dual LEV on a model dragonfly wing (AR=5.8), observed in a previous study (Y.L., G.X.S. and W. H. Su, manuscript submitted for publication). The wing was at mid-downstroke with mid-stroke angle of attack m=60°.

View larger version (9K): [in this window] [in a new window]   Fig. 2. Model wing planforms with a range of aspect ratios (AR). Except for the wing with AR=10 and the model fruit fly wing, which had an effective wingspan r of 154 mm and 129 mm, respectively, for all the others r=104 mm.

View larger version (18K): [in this window] [in a new window]   Fig. 3. Sketch of flapping motion in hovering. (A) Left: spatial configuration of the flapping motion of a model wing. The thick black line denotes the leading edge; OT, translational axis; OZ, rotational axis; OD and OU, the translational extreme positions; R, model wing length; r, effective model wing length; , stroke amplitude; , instantaneous translational angle. Right: the motion of a section of the wing. , instantaneous angle of attack; , instantaneous rotational angle (=90-°); black thick line denotes wing section and solid-dot, the leading edge. (B) The kinematic curves over one period. The translational and rotational angular positions are normalized using and m (maximal rotational angle), respectively. The black line at t/T=0.25 denotes the DPIV triggering phase.

View larger version (27K): [in this window] [in a new window]   Fig. 4. Flow visualization by the dye release method.

View larger version (16K): [in this window] [in a new window]   Fig. 5. DPIV setup. (A) Typical velocity vectors. The black thick line denotes wing section and the solid-dot the leading edge. The white area in front of the wing represents the shadow due to the nontransparency of the aluminum wing. Scale bar, 200 mm s-1. (B) Sketch of DPIV arrangement. The large gray arrow denotes the positioning translation of the model system. X and Z are two axes in the horizontal plane, while Y heads vertically away from the ground; z, the distance between the wing-base and the laser-sheet; r, the effective wing length. The laser-sheet and CCD were always perpendicular and parallel to Z, respectively.

View larger version (32K): [in this window] [in a new window]   Fig. 6. (A-D) Dye flow visualization showing the dual LEV evolution over one stroke (T; AR=5.8, m=6°, =60°, Re=1624).

View larger version (37K): [in this window] [in a new window]   Fig. 7. DPIV results at mid-downstroke (0.25T, the same phase as Fig. 6B). (A) A typical result at 0.29r (effective model wing length r=104 mm). The black thick line denotes wing section and the solid-dot the leading edge. Sectional streamlines are plot. The pseudocolor contour represents the spanwise vorticity. (B) Sectional flow fields at different spanwise locations. The slices were spaced by 15 mm and were all perpendicular to the spanwise direction. Plot representation as in A.

View larger version (70K): [in this window] [in a new window]   Fig. 8. Dual LEV in various m conditions (AR=5.8, =60°, Re=1624). Visualization pictures were captured at mid-downstroke (0.25T). Sectional flow fields at 0.29r were measured via DPIV at the same phase as the visualization pictures. Plot representation as in Fig. 7A.

View larger version (64K): [in this window] [in a new window]   Fig. 9. Dual LEV in various Re conditions (AR=5.8, m=60°, =60°). Visualization pictures were captured at mid-downstroke (0.25T). Sectional flow fields at 0.29r were measured via DPIV at the same phase as the visualization pictures. Plot representation as in Fig. 7A.

View larger version (40K): [in this window] [in a new window]   Fig. 10. Dual LEV in various AR conditions (m=40°). Visualization pictures were captured at mid-downstroke (0.25T). Sectional flow fields at 0.29r were measured via DPIV at the same phase as the visualization pictures. Plot representation as in Fig. 7A.

View larger version (34K): [in this window] [in a new window]   Fig. 11. Dual LEV on model fruit fly wing (AR=3.1, m=40°, =150°, Re=1889). The results were captured or measured at mid-downstroke (0.25T). (A) Dye visualization picture. (B) DPIV result at 0.35r (r=129 mm). Plot representation as in Fig. 7A. (C) Sectional flow structures at different spanwise locations. The DPIV slices were spaced by 15 mm.

View larger version (35K): [in this window] [in a new window]   Fig. 12. Global sectional flow structure. (A) DPIV result at 0.29r at mid-downstroke (AR=5.8, m=60°, =60°, Re=1624). Plot representation as in Fig. 7A; velocity vectors are shown. The in- and outboard blue vorticity concentrations correspond to the primary and minor vortices, respectively. The yellow and pink vorticity region behind the trailing edge is the shed trailing-edge vortex. Scale bar, 200 mm s-1. (B) Conjectured topological structure of the sectional flow field. F, focus; S, saddle; S', semi-saddle.