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GDR 23-24 Oct 2007

CHARACTERIZATION OF TYPICAL RESPONSE IN THE WAKE OF THE NACA0015 UNDER THE ACTION

OF FLUIDIC VORTEX GENERATORS

Siauw Wei Long*, Jean Tensi*, Jean Paul Bonnet*, Bernd Rainer Noack†, Laurent Cordier*

* LEA Poitiers† TU Berlin

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Objectives Model, experimental setup, flow condition & fluidic vortex generator BackgroundResults• Steady state characterization • Unsteady characterization & reduced order

modelingConclusion

Order of Presentation

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GDR 23-24 Oct 2007

Towards building a close loop flow control system -Identify the physics of the transient process of flow separation/attachment over a NACA0015

Objectives

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Model & Test Facility

Closed loop tunnelTest section 2.4m by 2.6mTurbulence intensity = 0.4% at ~40m/sNACA0015 airfoil (baseline model)

• Turbulated with 80micron grits• Equiped with pressure transducers at mid-span• Vortex generators installed (0.3c from leading edge) at

central 1/3 of span• Test at Re=1million (40m/s)

Test section

wind

Plan view of wing

2.4m

0.35

m

Externalbalance

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GDR 23-24 Oct 2007

Fluidic Vortex Generators

Solenoid valve

Solenoid valve

Solenoid valve

Solenoid valve

supply

Distribution chamber

Distribution chamber

Distribution chamber

Distribution chamber

x 11 orifices x 11 orifices x 11 orifices x 11 orifices

30o

60o

Single row of jet orifices orientated at 30o (pitch) and 60o (yaw)

Jet direction

•Single row of 44 angled orifices

•Generate co-rotating vortices

•Design to operate up to sonic jet velocity

•In windon condition:- 7msec for jet to be deployed

- 9 msec for jet to be removed

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Background

Several studies were conducted in LEA concerning the efficiency of various jet actuator configurations in attaching separated flow over airfoils since 2000 • Force balance, surface pressure data, surface flow visualization and PIV(documented in the thése of S. Bourgois )

EFFC 2005 showed that angled fluidic vortex generator in continuous mode was most efficient in attaching separated flow over NACA0015 up to 18deg incidence (Cl enhanced & Cd reduced).

(documented in IUTAM 2006 )

0.850.9

0.951

1.051.1

1.15

11 12 13 14 15 16alpha (deg)

Cl

baselineC_mu~0.27%, VR=2.5C_mu~0.36%, VR=3.5

α =15° baseline α =15°, Cµ~0.36%, VR~3.5

Flow Flow

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Background

(1) Find an efficient actuator configuration to attach separated flow over a wide range of incidences at Re~1million

(2) Find a suitable test condition to realize fundamental studies of the transient process of attachment and separation

(3) Build reduced order model of the condition described in (2)

Flow Flow

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GDR 23-24 Oct 2007

Steady Characterization : Efficiency in terms of CL

00.10.20.30.40.50.60.70.80.9

11.11.2

0 2 4 6 8 10 12 14 16 18 20 22

incidence

CL

C_mu=1.7%, VR=7.3C_mu=0.44%, VR=5.0baseline

CL estimated from integration of surface pressure distribution

(1) Better 2D estimate of CL

(2) Higher Cµ required to increase efficiency in post stall angles

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GDR 23-24 Oct 2007

Steady Characterization : Trace of longitudinal vortices

Wave length reduced by ~1/2 as we survey towards trailing edge of the airfoil

x/c=0.0286

x/c=0.154

x/c=0.286

Survey height =3mm above airfoil surface

x/c=0

11deg, 3bar(supply)

x/c=0.0286

x/c=0.286

x/c=0.154

Flow

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Trace of the spanwise evolution of longitudinal vortices over the airfoil.

Indication of vortex merging

(Pauley W.R. and Eaton J.K. “Experimental study of the development of longitudinalvortex pairs embedded in a turbulent boundary layer”, AIAA Journal, Vol. 26, n° 7, pages816 – 823, 1988)

Order of orifice

separation

x/c=0.0286x/c=0.154

x/c=0.286

x/c=0

x/c=0.286 x/c=0.0286z/c

Steady Characterization : Trace of longitudinal vortices

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GDR 23-24 Oct 2007

Spectral distribution (St*Euu) in the wake at x/c=1 from the trailing edgeWithout jet deployment With jet deployment

jet

y/c

x/c=1

Steady Characterization : Spectral distribution in the wake

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Unsteady Characterization

Study conducted at the following conditions:• 11deg incidence• Jet deployed at a frequency of 1Hz • Re=1mil (~40m/s)

Measurement technique• Hotwire• PIV

Test condition appreciation• Movement of tuffs at 11deg (C:\test2007\Videos actuation)• Movement of wake at 11 deg (C:\test2007\Videos actuation)

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Unsteady Characterization

PIV window in wake

PIV window over airfoil

Jet position

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Unsteady Characterization: Wake Survey

Wake survey at x/c=-1, using a single component hotwire

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Unsteady Characterization : Wake evolution during jet deployment

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Unsteady Characterization : Wake evolution during jet removal

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Evolution of the y-component of the velocity field during the process of jet deployment.

* Y component velocity becomes more –ve, indication of flow entrainment towards the wall

Unsteady Characterization : Evolution on airfoil during jet deployment

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Evolution of the y-component of the velocity field during the process of jet removal.

Unsteady Characterization : Evolution on airfoil during jet removal

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1. POD on time resolved assembled average PIV velocity field (the evolution is represented by 40 time instant, each time instant is based on ensemble average of 300 snap shots)

2. Extract the first relevant number modes and compute

3. Solve the system of linear equations

4. Simulate the dynamical system iijiji bDaCa +=

•

∑=

Φ+=nsnap

n

nnmean XtaUtXu

1

)()( )()(),(

ia•

Unsteady Characterization : Reduced order modeling

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Energy distribution of the eigen modes suggest 4 modes are sufficient to recover 99% of the flow characteristic.

Unsteady Characterization : Energy distribution

0 10 20 30 40 50 6075

80

85

90

95

100

mode number, n

( Σi=

1nλ i

/ Σj=

1Nλ j

)*10

0

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Results : Unsteady Characterization

0 5 10 15 20 25 30 35 40-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3Plot of the temporal coefficients, a1(t)

a1 (t)

T+=tU∞

/Lref

originial a1(t)calculated using PODpredicted a1(t)using LOD

0 5 10 15 20 25 30 35 40-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6Plot of the temporal coefficients, a2(t)

a2 (t)

T+=tU∞

/Lref

originial a2(t)calculated using PODpredicted a2(t)using LOD

0 5 10 15 20 25 30 35 40-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5Plot of the temporal coefficients, a4(t)

a4 (t)

T+=tU∞

/Lref

originial a4(t)calculated using PODpredicted a4(t)using LOD

0 5 10 15 20 25 30 35 40-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3Plot of the temporal coefficients, a3(t)

a3 (t)

T+=tU∞

/Lref

originial a3(t)calculated using PODpredicted a3(t)using LOD

Base on the evolution of the first mode T+~10

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Conclusion

A robust fluidic actuator has been validated up to incidence of 22deg at Re~1 millionFlow response time in the wake was determined to be • T+~10 (~25msec) for reattachment over the airfoil • T+~20 (~50msec) for separation over the airfoil

A linear reduced order modeling has been realized • Give possibility to explore other initial and actuation conditions• Give further insight to the physics of actuator deployment and removal