Flexible flaps for separation
control on a wing with low
aspect ratio
Dipl. Ing. G. Patone
Dr. W. Müller
Dr. R. Bannasch
Prof. Dr. Ing. I. Rechenberg
1
bionics pilot project:
Aeroflexible surface flaps
as "eddy-breaks"
built after the
covert feathers of birds
Project partners:
• DLR Abt. Turbulenzforschung
• Firma Stemme GmbH
• Fachgebiet Bionik und Evolutionstechnik an der
TU-Berlin
2
main objective:
0
1
eddy
2
3
3
Brown Skua with “eddy-flaps”
2
eddy
3
lifted covert feathers
0
1
2
3
eddy- flaps
4
aerofoil with eddy- flaps
0
1
eddy- flaps
2
3
5
goal:
not like this
but like this
cL
cL
cD
a
cL
cL
a
cD
6
research goal
• improving the stall behavior of an
aerofoil
• flaps should not have any negative
effects while not active
• flaps should work without external
controls
7
experimental setup at the wind tunnel
lift-balance
wind tunnel
10m/s
NACA 2412 aerofoil with an
aspect ratio of 3.5
Re= 130.000
drag-balance
pressure sensor and scanivalve
8
porosity
schematic pressure distribution
px
a
+
py
px > p y
px
px
py
py
b
py
impervious
materials are
lifted off by the
pressure
differences
px
c
py
py
porous materials
remain
on the surface
9
aerofoil with silk flaps
700m
m
silk
steel wire
100
a
200mm
10
silk flaps
b
a
t
NACA 2412
CL
1
0,9
0,8
0,7
0,6
0,5
0,4
0,3
without flaps
with silk flaps ( a=15%t; b=50%t)
0,2
0,1
0
0
10
20
30
a
40
11
polar diagram for ‘perforated plastic sheet’ flaps
b
a
t
NACA 2412
CL
1
0,9
0,8
0,7
0,6
0,5
0,4
0,3
`perforated plastic sheet` flaps
(a=15%t, b=35%t)
fixed `perforated plastic sheet` flaps
0,2
0,1
0
0
10
20
30
a
40
12
aerofoil for pressure distribution
7
6
5
4
3
2
1
13
pressure distribution
at 16 degrees
a = 20°:
without flaps
-0.0
-0.0
-0.6
-0. 3
-0.1
-0.6
-0.
5
-0.7
-0.5
-0. 2
5
-0.
-1.7
-2.1
-2.0
-2.1
-1.9
-1.5
-1.6
-0.7 -0. 6
-1.2 -0-1. 9 -0
-1. -1. . 1 . 8
4 3
-1.8
with flaps
-0. 2
-0. 5
-0.7
-0.6
-0.5
.2
-0
-0.3 -0.4
-0. 5
-0. 6
.2
-0
-0.1
-0.1
-0. 2
-0.1
-0.4
-0.3
.4
-0
-0.4
-0.4
-1.9
-1.7
-1.5
. 91
-0-1.
-1.6
-1.8
-0.4
-0.5
-0.6
-0.7
-0
-1.3-1.2 . 8
-1.4
incident airflow
14
pressure distribution
at 19 degrees
a = 23°:
without flaps
-0.6
-0.4
-0. 5
-0.4
-0.
7
-0.3
-0.5
6
-0. -0. 5
-0. 5
-0. 6
-0.8 -0. 7
-1. 2 -1.1 -0. 9
-0. 5
-0.7
-0
.8
-1.1 -0. 9
-1.2
-0. 6
with flaps
-0.5
-0. 4
-0.3
-0. 8
-0.5
-0.
4
-0. 7
-0. 6
-0.5
-0.7
-0.3
-0.
4
6
-0.
-0
.4
-0.3
-0.7 -0.6
-1.7
-1.6
-1.2
-1
-1.4
.5 -1.3
-0.9
-1.
1
-1.6-1.5
-1.7
-0.9
-1.1 -0.8
-11. 3-1. 2
.4
incident airflow
15
flow visualisation
trapped
vortex
stationärer
Wirbel
trapped eddy
instationäre Strömungsverhältnisse
16
pressure distribution
at 36 degrees
a = 40°:
without flaps
.4
-0
-0.4
-0.4
-0. 4
-0.4
-0
.5
with flaps
-0. 6
7
-0.
-0.8
-0. 8
-0.4
-0.8
incident airflow
17
polar diagram (calculated
from all measuring rows)
CL
1
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
without flap
with flap
0,1
0
0
10
20
30
a
40
a
18
CL
lift distribution without flaps
at different angles of attack
1
18°
0,9
0,8
0,7
24°
19°
0,6
36°
0,5
6°
0,4
0,3
1°
0,2
0,1
0
0
100
200
300
400
500
600
mm
700
19
CL
lift distribution with flaps at
different angles of attack
1
18°
0,9
24°
0,8
0,7
36°
19°
0,6
0,5
6°
0,4
0,3
1°
0,2
0,1
0
0
100
200
300
400
500
600
mm
700
20
summary:
• eddy flaps prevent sudden drop in
lift generation during stall
• pressure distribution indicates:
eddy-flaps restrict eddy to hind part
of aerofoil
outlook:
• automatic contour adapting flaps
• dynamic stall behaviour
21

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