Effective aerodynamics at Reynolds numbers lower than 10 000 is of great technological interest and a fundamental scientific challenge. The current study covers a Reynolds number range of 2000–8000. At these Reynolds numbers, natural insect flight could provide inspiration for technology development. Insect wings are commonly characterized by corrugated airfoils. In particular, the airfoil of the dragonfly, which is able to glide, can be used for two-dimensional aerodynamic study of fixed rigid wings. In this study, a simplified dragonfly airfoil is numerically analyzed in a steady free-stream flow. The aerodynamic performance (such as mean and fluctuating lift and drag), are first compared to a “traditional” low Reynolds number airfoil: the Eppler-E61. The numerical results demonstrate superior performances of the corrugated airfoil. A series of low-speed wind and water tunnel experiments were performed on the corrugated airfoil, to validate the numerical results. The findings indicate quantitative agreement with the mean wake velocity profiles and shedding frequencies while validating the two dimensionality of the flow. A flow physics numerical study was performed in order to understand the underlying mechanism of corrugated airfoils at these Reynolds numbers. Airfoil shapes based on the flow field characteristics of the corrugated airfoil were built and analyzed. Their performances were compared to those of the corrugated airfoil, stressing the advantages of the latter. It was found that the flow which separates from the corrugations and forms spanwise vortices intermittently reattaches to the aft-upper arc region of the airfoil. This mechanism is responsible for the relatively low intensity of the vortices in the airfoil wake, reducing the drag and increasing the flight performances of this kind of corrugated airfoil as compared to traditional low Reynolds number airfoils such as the Eppler E-61.

1.
T. J.
Mueller
and
J. D.
DeLaurier
, “
An overview of micro air vehicles aerodynamics
,”
Prog. Astronaut. Aeronaut.
195
,
1
(
2001
).
2.
H.
Schlichting
and
K.
Gersten
,
Boundary Layer Theory
, 8th ed. (
Springer-Verlag
,
Berlin
,
1999
), p.
31
.
3.
J. D.
Anderson
,
Fundamentals of Aerodynamics
, 3rd ed. (
McGraw-Hill
,
Blacklick, Ohio
,
2000
), pp.
307
308
.
4.
G. B.
McCulllough
and
D. E.
Gault
, “
Examples of three representative types of airfoil section stall at low-speed
,” NACA Report No. TN 2502,
1951
.
5.
I.
Tani
, “
Low-speed flows involving bubble separations
,”
Prog. Aeronaut. Sci.
5
,
70
(
1964
).
6.
R. F.
Huang
and
C. L.
Lin
, “
Vortex shedding and shear-layer instability of wing at low Reynolds numbers
,”
AIAA J.
33
,
1398
(
1995
).
7.
Z. J.
Wang
, “
The role of drag in insect hovering
,”
J. Exp. Biol.
207
,
4147
(
2004
).
8.
B. G.
Newman
,
S. B.
Savage
, and
D.
Schouella
, “
Model test on a wing section of a dragonfly
,” in
Scale Effects in Animal Locomotion
, edited by
T. J.
Pedley
(
Academic
,
London
,
1977
), pp.
445
477
.
9.
J. M.
Wakeling
and
C. P.
Ellington
, “
Dragonfly flight
,”
J. Exp. Biol.
200
,
543
(
1997
).
10.
R. J.
Wooton
,
K. E.
Evans
,
R.
Herbert
, and
W.
Smith
, “
Morphology and operation of the locust hind wing
,”
J. Exp. Biol.
203
,
2921
(
2000
).
11.
A. B.
Kesel
,
U.
Philippi
, and
W.
Nachtigall
, “
Biomechanical aspects of insects' wings: An analysis using the finite element method
,”
Comput. Biol. Med.
28
,
423
(
1998
).
12.
C. J. C.
Rees
, “
Aerodynamic properties of an insect wing section and a smooth aerofoil compared
,”
Nature (London)
258
,
141
(
1975
).
13.
R. H.
Buckholtz
, “
The functional role of wing corrugations in living systems
,”
ASME J. Fluids Eng.
108
,
93
(
1986
).
14.
M.
Okamoto
,
K.
Yasuda
, and
A.
Azuma
, “
Aerodynamic characteristics of the wings and body of a dragonfly
,”
J. Exp. Biol.
199
,
281
(
1996
).
15.
A. B.
Kesel
, “
Aerodynamic characteristics of dragonfly wing sections with technical aerofoils
,”
J. Exp. Biol.
203
,
3125
(
2000
).
16.
S.
Sunada
,
A.
Sakaguchi
, and
K.
Kawachi
, “
Airfoil section characteristics at a low Reynolds number
,”
ASME J. Fluids Eng.
119
,
129
(
1997
).
17.
S.
Sunada
,
T.
Yasuda
,
K.
Yasuda
, and
K.
Kawachi
, “
Comparison of wing characteristics at an ultralow Reynolds number
,”
J. Aircr.
39
,
331
(
2002
).
18.
H.
Gao
,
H.
Hu
, and
Z. J.
Wang
, “
Computational study of unsteady flows around dragonfly and smooth airfoils at low Reynolds numbers
,”
46th AIAA Aerospace Sciences Meeting and Exhibit
(
AIAA
,
Reno, NV
,
2008
), Paper No. 2008-385.
19.
A.
Vargas
,
R.
Mittal
, and
H.
Dong
, “
A computational study of the aerodynamic performance of a dragonfly wing section in gliding flight
,”
Bioinspir. Biomim.
3
,
026004
(
2008
).
20.
R.
Eppler
,
Airfoil Design and Data
(
Springer-Verlag
,
Berlin
,
1990
).
21.
E. V.
Laitone
, “
Aerodynamic lift at Reynolds numbers below 7×104
,”
AIAA J.
34
,
1941
(
1996
).
22.
B. W.
McCormick
,
Aerodynamics, Aeronautics, and Flight Mechanics
(
Wiley
,
New York
,
1979
), p.
137
.
23.
S.
Brokman
and
D.
Levin
, “
A flow visualization study of the flow in a 2 D array of fins
,”
Exp. Fluids
14
,
241
(
1993
).
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