1

Flexible flaps for separation control on a wing with low

aspect ratio

Dipl. Ing. G. Patone

Dr. W. MüllerDr. R. Bannasch

Prof. Dr. Ing. I. Rechenberg

2

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

3

main objective:

eddy

4

Brown Skua with “eddy-flaps”

lifted covert feathers 0

1

2

3 eddy- flaps

eddy

5

0

1

2

3

aerofoil with eddy- flaps

eddy- flaps

6

cL

goal:

not like this but like this

cL

cL cL

cD

cD

7

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

8

experimental setup at the wind tunnel

lift-balance

wind tunnel10m/s

drag-balance pressure sensor and scanivalve

NACA 2412 aerofoil with an aspect ratio of 3.5

Re= 130.000

9

porosity

px

pypxpypy

px

py

-

+

px

pypy

a

b c

schematic pressure distribution

px > py

impervious materials are lifted off by the pressure differences

porous materials remainon the surface

10

200mm

700m

m

100a

aerofoil with silk flaps

silk

steel wire

11

silk flaps

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 10 20 30 40

CL

without flaps

with silk flaps ( a=15%t; b=50%t)

NACA 2412

t

ba

12

polar diagram for ‘perforated plastic sheet’ flaps

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 10 20 30 40

CL

`perforated plastic sheet` flaps(a=15%t, b=35%t)fixed `perforated plastic sheet` flaps

NACA 2412

t

ba

13

aerofoil for pressure distribution

7

6

54321

14

pressure distribution at 16 degrees

incident airflow

without flaps

with flaps

15

pressure distribution at 19 degrees

incident airflow

without flaps

with flaps

16

flow visualisation

stationärer Wirbel instationäre Strömungsverhältnisse

v

trapped vortex trapped eddy

17

pressure distribution at 36 degrees

incident airflow

without flaps

with flaps

18

polar diagram (calculated from all measuring rows)

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 10 20 30 40

CL

without flap with flap

19

lift distribution without flaps at different angles of attack

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 100 200 300 400 500 600 700mm

CL

18°

19°

36°

1°

24°

6°

20

lift distribution with flaps at different angles of attack

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 100 200 300 400 500 600 700mm

CL

18°

19°36°

1°

24°

6°

21

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