FLOWCOMAG

April 1–2, 2004

SFB 609

Seawater Flow Transition and Separation Control

Tom Weier, Thomas Albrecht, Gerd Mutschke, Gunter Gerbeth

Wall–parallel Lorentz force

NS

SN

NS

SN a

+ +z

xy

∞U

LSN S

N− + −

3

410

10

10

10

2

1F [N/m ]3

j = σ(E + u×B)

F = j×B = Fex

F =π

8j0M0e

−πay

Gailitis, Lielausis 1961

u?∂u?

∂x? + v?∂u?

∂y? = ∂2u?

∂y?2+ Ze−y

?

x? = νπ2xU∞a2, y

? = πay, u

? = uU∞, v

? = vaπν

Z = j0M0a2

8πρU∞ν = 1 : uU∞ = 1− e−πay

Laminar Boundary Layer with Lorentz force Reδ1 = 290

0

5

10

15

20

25

30

35

40

10.5010.5010.5010.50

y/m

m

u/U∞

x=0mm

x*=0

x=150mm

x*=0.18

x=350mm

x*=0.43

x=550mm

x*=0.68

Z=0Z=1.2exp. profileBlasius profile

Transition: T–S waves for Reδ1 = 585, a = 3.475δ1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 100 200 300 400 500 600 700

u(y

=δ 1

)/U

∞

x/δ1

Z=0, no TSZ=0, TSZ=1, x= 5Z=1, x=300

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 100 200 300 400 500 600 700

u(y

=δ 1

)/U

∞

x/δ1

Z00.050.10.20.40.8

Transition: 3D disturbance for Reδ1 = 585, a = 3.475δ1

z

δ1

0 20

10

20y

δ1

0

100

200

x

δ1

isosurfacesQ = 0.4

Z = 0Z = 0.1

Separation suppression at an inclined flat plate

Hydrofoils with electrodes and magnets

NACA 0015 (left):c = 0.667ma/c = 0.015B0 = 0.58Tstainless steel electrodes

PTL IV (right):c = 0.158ma/c = 0.03B0 = 0.2TTi with RuO2/IrO2

(DSA)

NACA 0015 in parallel flow

CµEMHD = aj0B02ρU2∞

· xe−xsc

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

CL

Cµ EMHD

Re=1.16·105

Re=1.82·105

Re=3.08·105

Re=3.71·105

CL = 0.843 · C0.521µEMHD

-0.4

-0.35

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

CD

Cµ EMHD

Re=1.16·105

Re=1.82·105

Re=3.08·105

Re=3.71·105

CD = 0.024− 1.01 · CµEMHD

Reattachment: Comparison to steady blowing

0

0.2

0.4

0.6

0.8

1

1.2

0 0.02 0.04 0.06 0.08 0.1

∆CL

CµEMHD

Re=3.4 ·104

Re=4.8 ·104

Re=5.8 ·104

PTL IVα=17° BLC

Circulation Control

0

0.5

1

1.5

2

0 0.05 0.1 0.15 0.2

∆CL

Cµ

0.35% c0.42% c0.45% c0.61% c

Maximum lift gain

0

0.5

1

2

0 5 10 15 20 25 35

CCL

Lmax

α[°]

Cµ EMHD =0Cµ EMHD =0.045

5Re=3.0·10 ∆NACA 0015

∆CLmax(Cµ, Re) = CLmax(Cµ, Re)− CLmax(Cµ = 0, Re)

Maximum lift gain versus CµEMHD

∆CLmax = 3.02 · C0.585µEMHD

0.01

0.1

1

10

0.001 0.01 0.1 1

∆CLm

ax

CµEMHD

PTL IV a/c=0.06PTL IV a/c=0.03NACA 0015 a/c=0.015Numerics

Oscillatory forces: Motivation

0.5

1

1.5

2

3

−10 −5 0 5 10 20

CL

α [°]

baselineF+=0 Cµ=1%F+=1.75 C’µ=0.015%

Darabi, A.Wygnanski, I.1996

Seifert, A.

Lorentz force configurations compared

stationary:

U∞

xs

xe

CµEMHD =1

2· aj0B0

ρU2∞· xe − xs

c

oscillatory:

F+ =fec

U∞

U∞

xs xe

C ′µeff =1

2· aj0effB0

ρU2∞· xe − xs

c

,

NACA 0015 in the test section

c = 160 mms = 240 mmxa = 15 mma = 5 mmB0 = 0.33 T

Lift- and drag coefficient versus excitation frequency,

α = 20◦, Re = 5.2 · 104

0.6

0.7

0.8

0.9

1

1.1

1.2

0 2 4 6 8 10

CL

F+

c’µeff

0.28%

0.56%

0.83%

1.11%

0.26

0.3

0.34

0.38

0.42

0.46

0 2 4 6 8 10

CD

F+

Comparison to oscillatory blowing on a NACA 0015

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 5 10 15 20 25

CL

α / o

c’µeff

Re=5.2·104, F+=0.5

0

0.06%

0.28%

0.56%

0.84%

1.11%

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 5 10 15 20C

L

α / o

c’µeff

Greenblatt, D.Wygnanski, I.2000Re=1.5·105, F+=1.1

00.1%1.3%

Lift increase at constant angle of attack

−0.2

−0.1

0

0.1

0.2

0.3

0.4

0.5

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

∆CL

CµEMHD/[%]

F+=1

Re=5·104

α=17°

stationary forcingperiodic excitation

Maximum lift gain

PSfrag replacements

CL

α

max ∆CL

∆CLmax

∆CLcirc-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 0.2 0.4 0.6 0.8 1 1.2

∆CLm

ax

c’µeff/%

NACA 0012, Re=2.4·105, F+=1.5Greenblatt, D., Wygnanski, I. 2000

Conclusions

Transition delay:

• exponential profile• T–S waves and 3D disturbances are damped

Separation control by stationary Lorentz force:

• separation & circulation can be controlled• power consumption (too) high (for applications)

Separation control by oscillatory Lorentz force:

• characteristic phenomena comparable to alternativemethods in a quantitative sense

➡ comparable gain in efficiency achievable (?)