NEAR WALL MEASUREMENTS IN A SEPARATING TURBULENT … 3/S3_Le… · •Laser Doppler Velocimetry...

Open Workshop, Lille, April 21-23, 2009

Università di GenovaDipartimento di Macchine, Sistemi Energetici e TrasportiAerodynamics and Turbomachinery Laboratory

NEAR WALL MEASUREMENTS IN A SEPARATING TURBULENT BOUNDARY LAYER WITH AND WITHOUT

PASSIVE FLOW CONTROL

Davide Lengani, Daniele Simoni, Marina Ubaldi, Pietro ZuninoUniversità degli Studi di Genova (Italy)

Dipartimento di Macchine, Sistemi Energetici e Trasporti

Aerodynamics and Turbomachinery Laboratory

Francesco BertiniAVIO S.p.A.

Torino, Italy



Objectives

•Experimental analysis of a separating turbulent boundary layer developing on a large scale flat plate with prescribed adverse pressure gradient

•Measurements have been performed in the symmetry plane of a linear diffuser for a baseline uncontrolled condition and then repeated with passive control devices: low-profile vortex generators

•Laser Doppler Velocimetry employed to obtain high spatial resolution and accurate statistical analysis of boundary layer velocity and turbulence profiles

•The three-dimensional effects induced by the Vortex Generators have been also investigated in a cross-stream plane

This work is part of the joint European research project Aggressive Intermediate Duct Aerodynamics for Competitive & Environmentally Friendly Jet Engines

Priority 4 Aeronautics & SpaceSpecific Targeted REsearch Project

AST3-CT-2003-502836



Open-loop wind tunnel with variable pressure discharge

Inlet boundary layer parameters and free-stream turbulence intensity

1%0.0032110001.245.6 mm80 mm

TucfReθH12θδ

Test section

UNIGE-AVIO test rig for boundary layer separation control experiments



Large scale flat plate boundary layer experimentswith adverse pressure gradients

Flat plate prescribed pressure distributions through variable top wall inclination with boundary layer suction

Test section top wall inclination 16°Ideal acceleration factor

7

01

0120

1016.3)()( −⋅−=

−−

=XXUU

UK ν

x

y

z

first measuring plane

0 1 2 3 4 5x/H0

0

0.2

0.4

0.6

0.8

Cp=

2(p s

-ps0

)/ρu 0

2

No VGsVGs

• Flat plate: 1700 mm long, 400 mm wide • Test section inlet height: 196 mm• Inlet boundary layer suction on lateral

and top walls



Vortex generators geometry

25°β

23°α

80mmδs

16mm0.2*δc

64mm0.8*δl

16mm0.2*δh

Geometrical parameters

VGs axial position:95 mm upstream of the detachment point (t.e. x=290 mm)

co-rotating pattern

counter-rotating with respect to the center line



Laser Doppler Velocimetry instrumentation

Four beams LDV main characteristics:DANTEC FlowLite 2D•200 mW 532 nm and 200 mW 488 nm solid state lasers

•one of each pair of beams frequency shifted by a Bragg cell (40 MHz)

Optical probe characteristics• Diameter D=60 mm• Beam separation before expansion d= 38 mm

• Focal length f=300 mm• Beam intersection angle θ = 7.2°• Fringe separation δ= 4.1 μm (green) 3.8 μm (blue)

• Probe volume 0.09x0.09x1.4 mmBurst Processors

• 2 Dantec Enhanced Burst Spectrum Analysers operated in coincidence mode

Probe Traversing Mechanism• Computer controlled 3-axis mechanism with minimum step of 8 μm

Measurements matrix

• 14 traverses normal to the surface • 103 points per traverse• 30000 samples per point or record length in

time of 120 s



Laser Doppler Velocimetry instrumentation

Measurements matrix

• traverses normal to the surface • 103 points per traverse• 30000 samples per point or record length in

time of 120 s

x [mm]

0

100

200

300

400

500y

[mm

]

0

50

100

150

z [mm]

0

100

x

y

z

first measuring plane



Mean velocity distribution without VGs

• Streamwise reduction of the freestream velocity (adverse pressure gradient) and progressive boundary layer momentum reduction.

• Positive normal velocity component in the freestream (top wall inclination, b. l. suction)

• Detachment point (zero mean velocity gradient in y direction at the wall): x = 385 mm

0 1 2 3 4 5x/H0

0

0.2

0.4

0.6

0.8

Cp=

2(p s

-ps0

)/ρu 0

2

No VGsVGs

0 10 20 30u [m/s]

0

40

80

120

y [m

m]

No VGs, x=0mmNo VGs, x=200mmNo VGs, x=350mmNo VGs, x=385mm



Mean velocity distribution with and without VGs

• Vortex Generators delaying separation thanks to momentum transferred toward the wall

• Higher diffusion of the flow characterizes the controlled condition

0 1 2 3 4 5x/H0

0

0.2

0.4

0.6

0.8

Cp=

2(p s

-ps0

)/ρu 0

2

No VGsVGs

0 10 20 30u [m/s]

0

40

80

120

y [m

m]

VGs x=350mmNo VGs, x=0mmNo VGs, x=200mmNo VGs, x=350mmNo VGs, x=385mm



Dissipation mechanisms

⎟⎟⎠

⎞⎜⎜⎝

⎛−

∂∂

∂∂

−⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛−

∂∂

∂∂

+⎟⎠⎞

⎜⎝⎛ −

∂∂

∂∂

−⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛ −

∂∂

∂∂

+

=∂∂

+∂

∂+

∂

∂

''1''1'1'1

)2()2(

22

22

vuyu

yuvu

yuu

yu

xu

xuu

xuu

x

xpu

y

uv

x

uu

ρμρ

ρμρ

ρμρ

ρμρ

ρ

⎟⎠⎞

⎜⎝⎛ −

∂∂

∂∂

−⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛ −

∂∂

∂∂

+⎟⎟⎠

⎞⎜⎜⎝

⎛−

∂∂

∂∂

−⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛−

∂∂

∂∂

+

=∂∂

+∂

∂+

∂

∂

''1''1'1'1

)2()2(

22

22

vuxv

xvvu

xvv

xv

yv

yvv

yvv

y

ypv

y

vv

x

vu

ρμρ

ρμρ

ρμρ

ρμρ

ρ

2

)( ⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

=yuD Lxt μ

yuvuD Txt ∂∂

−= '')( ρxuuD Txn ∂∂

−=2

')( ρ

2

)( ⎟⎠⎞

⎜⎝⎛∂∂

=xuD Lxn μ

yvvD Tyn ∂∂

−=2

')( ρ

2

)( ⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

=yvD Lyn μ

2

)( ⎟⎠⎞

⎜⎝⎛∂∂

=xvD Lyt μ

xvvuD Tyt ∂∂

−= '')( ρ



Dissipation mechanisms: inlet boundary layer

-1000 0 1000 2000 3000Deformation works [W/m3]

0

40

80

120

y [m

m]

NO VGs(Dt)Tx, x=0mm(Dt)Lx, x=0mm

2

)( ⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

=yuD Lxt μ

yuvuD Txt ∂∂

−= '')( ρ

0 10 20 30u [m/s]

0

40

80

120

y [m

m]




Dissipation mechanisms: x=200 mm


0

40

80

120

y [m

m]

NO VGs(Dt)Tx, x=200mm(Dn)Tx, x=200mm

2

)( ⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

=yuD Lxt μ

yuvuD Txt ∂∂

−= '')( ρ

xuuD Txn ∂∂

−=2

')( ρ

0 10 20 30u [m/s]

0

40

80

120

y [m

m]




Dissipation mechanisms: BL approaching separation

yuvuD Txt ∂∂

−= '')( ρ

xuuD Txn ∂∂

−=2

')( ρ

0 10 20 30u [m/s]

0

40

80

120

y [m

m]



0

40

80

120

y [m

m]

NO VGs(Dt)Tx, x=200mm(Dn)Tx, x=200mm(Dt)Tx, x=350mm(Dn)Tx, x=350mm



Dissipation mechanisms: energy re-distribution effect

yuvuD Txt ∂∂

−= '')( ρ

xuuD Txn ∂∂

−=2

')( ρ

yvvD Tyn ∂∂

−=2

')( ρ

0 10 20 30u [m/s]

0

40

80

120

y [m

m]



0

40

80

120

y [m

m]

NO VGs(Dt)Tx, x=350mm(Dn)Tx, x=350mm(Dn)Ty, x=350mm



Vortex generators

25°β

23°α

80mmδs

16mm0.2*δc

64mm0.8*δl

16mm0.2*δh


VGs axial position:95 mm upstream of the detachment point (t.e. x=290 mm)

0 10 20 30u [m/s]

0

40

80

120

y [m

m]




Dissipation mechanisms with Vortex Generators

yuvuD Txt ∂∂

−= '')( ρ

xuuD Txn ∂∂

−=2

')( ρ

yvvD Tyn ∂∂

−=2

')( ρ

0 10 20 30u [m/s]

0

40

80

120

y [m

m]



0

40

80

120

y [m

m]

(Dn)Tx, No VGs(Dn)Tx, VGs




yuvuD Txt ∂∂

−= '')( ρ

xuuD Txn ∂∂

−=2

')( ρ

yvvD Tyn ∂∂

−=2

')( ρ

0 10 20 30u [m/s]

0

40

80

120

y [m

m]



0

40

80

120

y [m

m]

(Dt)Tx, No VGs(Dt)Tx, VGs




yuvuD Txt ∂∂

−= '')( ρ

xuuD Txn ∂∂

−=2

')( ρ

yvvD Tyn ∂∂

−=2

')( ρ

0 10 20 30u [m/s]

0

40

80

120

y [m

m]



0

40

80

120

y [m

m]

(Dn)Ty, No VGs(Dn)Ty, VGs




yuvuD Txt ∂∂

−= '')( ρ

xuuD Txn ∂∂

−=2

')( ρ

yvvD Tyn ∂∂

−=2

')( ρ

0 10 20 30u [m/s]

0

40

80

120

y [m

m]



0

40

80

120

y [m

m]

VGs x=350mm(Dt)Tx

(Dn)Tx

(Dn)Ty



Dissipation mechanisms: comparison of total contribution (x=350 mm)


0

40

80

120

y [m

m]

D'', No VGsD'', VGs



Vortex generators

25°β

23°α

80mmδs

16mm0.2*δc

64mm0.8*δl

16mm0.2*δh


1 entire pitch investigated in a cross-stream plane downstream the VGs

x [mm]

0

100

200

300

400

500

y[m

m]

0

50

100

150

z [mm]

0

100



3D effects of Vortex Generators

z [mm]

y[m

m]

0 20 40 60 800

20

40

60

80

100

120

20.0

17.8

15.6

13.3

11.1

8.9

6.7

4.4

2.2

0.0

u[m/s]

z [mm]

y[m

m]

0 20 40 60 800

20

40

60

80

100

120

4.03.63.32.92.52.11.81.41.00.70.3

rms(u')[m/s]



3D effects of Vortex Generators

z [mm]y

[mm

]0 20 40 60 80

0

20

40

60

80

100

120

20.0

17.8

15.6

13.3

11.1

8.9

6.7

4.4

2.2

0.0

u[m/s]

-4 -2 0 2 4u'v' [m2/s2]

0

40

80

120

y [m

m]

No VGsVGs z=0mmVGs z=10mmVGs z=25mmVGs z=70mm



Conclusions

• In the framework of the European project AIDA on Aggressive Intermediate Duct Aerodynamics experiments on separated and controlled turbulent boundary layerhave been carried out.

• LDV results provide a description of the separating turbulent boundary layer operating under a prescribed adverse pressure gradient

• Different contributions on the dissipation mechanisms have been distinctly analyzed: normal turbulent terms appear the greatest for a separating turbulent boundary layer.

• For the uncontrolled case the normal contribution along the y direction is negativeand tends to re-transfer energy to the mean motion.

• For the controlled case losses are contained thanks to the separation delaying.

• Future activity will be focused on total pressure measurements and loss production mechanism evaluation for baseline and controlled experiment, with three-dimensional losses evaluation for the controlled case.



Backflow color plot

Detachment point (detected at x=385mm)

The greatest low frequency oscillations appear for BF=0.5



Distributions of the streamwise momentum transported by the v velocity component downstream of VGs

-40 -20 0 20 40uv [m2/s2]

0

10

20

30

40

y [m

m]

x = 350 mmx = 400 mmx = 450 mmx = 500 mmx = 550 mmx = 600 mm

yvu

yvu

yu

xu

xu

xp

xu

∂∂

−∂∂

−∂

∂+

∂∂

−∂

∂+

∂∂

−=∂

∂ '''1)(2

22

2

22νν

ρ

•Minimum for y = 18 mm (comparable with VGs height) •Maximum negative peak for x = 350 mm (vanishes beyond x = 500 mm)

x-momentum equation for steady 2D incompressible flow:

accelerates the flow in the x direction for y < 18 mm, and decelerates the flow for y > 18 mm

Distortion in the mean velocity profile

0 5 10 15 20 25u [m/s]

0

40

80

120

160

y [m

m]

x = 400 mm



x [mm]

y[m

m]

0 100 200 300 400 500 6000

50

100

150

2000 0.003 0.006 0.009 0.012 0.015 0.018 0.021 0.024

Ti [s]

Flow Integral Time Scale

Detachment point (detected at x=385mm)

Free stream structures at wind tunnel test section inlet

Low integral time scale in the region of attached boundary layer

large integral time scale inside the separated flow region



Reynolds shear stress distribution with VGs

• Reynolds shear stress transport mechanism not negligible

-4 -2 0 2 4u'v' [m2/s2]

0

40

80

120

160

y [m

m]

• Reynolds shear stress gradient changes its sign as a function of the distance from the wall

−∂(u v)/∂y>0

−∂(u v)/∂y<0

VGs inlet boundary layer uv effect VGs outlet boundary layer

y [mm]

4020

u u u

−∂(u' v')/∂y<0 −∂(u' v')/∂y>04020

y [mm]

u u u

VGs outlet boundary layer Reynolds stress effect Uniformized boundary layer

x = 400 mm• Reynolds shear stress always acts in the sense of making uniform the velocity profile previously distorted by VGseffect

vu ⋅

NEAR WALL MEASUREMENTS IN A SEPARATING TURBULENT … 3/S3_Le… · •Laser Doppler Velocimetry...

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