Steady control of laminar Steady control of laminar separation over airfoils with separation over airfoils with

plasma sheet actuatorsplasma sheet actuators

Sosa RobertoSosa Roberto

Artana GuillermoArtana Guillermo

Laboratorio de Fluidodinámica, Universidad de Buenos Aires, CONICET,

Buenos Aires, Argentina

IntroductionIntroduction

In last years there has been a growing interest in In last years there has been a growing interest in the use of the use of ionization to add localized momentum ionization to add localized momentum to the flow by the collisions process of migrating to the flow by the collisions process of migrating charged particles with the neutral species of the charged particles with the neutral species of the airair

These EHD technologies have been considered These EHD technologies have been considered as good candidates to enhance the aerodynamic as good candidates to enhance the aerodynamic perfomance of airfoilsperfomance of airfoils

ObjectivesObjectives

In this work we study the improvement of In this work we study the improvement of the aerodynamic performance of an airfoil the aerodynamic performance of an airfoil at very low Re (Re<50000) by means of at very low Re (Re<50000) by means of an EHD actuatoran EHD actuator

Our study focuses on the relative distance Our study focuses on the relative distance of the actuator location and the position of of the actuator location and the position of separation line.separation line.

Flow configurations at low Re Flow configurations at low Re aerodynamicsaerodynamics

Position and size of the laminar bubble separation (LBS) changes with airflow velocity at a fixed angle and with the angle at a fixed airflow

Short LBSLarge LBS

LayoutLayout

1.1. Interest.Interest.

2.2. EHD actuators.EHD actuators.

3.3. Electromechanical coupling.Electromechanical coupling.

4.4. Experimental setup.Experimental setup.

5.5. Results & discussion.Results & discussion. Laminar boundary layer :Laminar boundary layer :

Partially attachedPartially attached With separationWith separation

• Laminar boundary layer partially separatedLaminar boundary layer partially separated• Laminar boundary layer fully separatedLaminar boundary layer fully separated

Flow with a laminar separation bubble (LSB)Flow with a laminar separation bubble (LSB)• Fully reattached turbulent boundary layerFully reattached turbulent boundary layer• With downstream separation of the reattached turbulent boundary layerWith downstream separation of the reattached turbulent boundary layer

6.6. Conclusions.Conclusions.

Some Area of InterestSome Area of InterestPower Control of Wind Turbines Power Control of Wind Turbines

Wind turbines are usually designed to produce electrical energy with Wind turbines are usually designed to produce electrical energy with a maximum output at wind speeds around 15 metres per second. a maximum output at wind speeds around 15 metres per second. In case of stronger winds it is necessary to waste part of the excess In case of stronger winds it is necessary to waste part of the excess energy of the wind in order to avoid damaging the wind turbine. energy of the wind in order to avoid damaging the wind turbine.

Around Around two thirds of the wind turbinestwo thirds of the wind turbines currently being installed in the currently being installed in the world are stall controlled machines. world are stall controlled machines. The geometry of the The geometry of the fixed angle bladesfixed angle blades profiles is designed to profiles is designed to ensure that the moment the wind speed becomes too high, it stalls. ensure that the moment the wind speed becomes too high, it stalls. This stall prevents the lifting force of the rotor blade from acting on This stall prevents the lifting force of the rotor blade from acting on the rotor the rotor

In practical application, In practical application, stall control is not very accuratestall control is not very accurate and many and many stall-controlled turbines do not meet their specifications. Deviations stall-controlled turbines do not meet their specifications. Deviations of the design-power in the order of tens of percent are regularof the design-power in the order of tens of percent are regular

Corona discharge.Corona discharge.

Dielectric barrier discharge.Dielectric barrier discharge.

Sliding discharge.Sliding discharge.

Kind of ehd actuatorsKind of ehd actuators

Previous research on ehd excited airfoilsPrevious research on ehd excited airfoils

Actuator off Actuator on

Near Post stall Regime Time averaged flow fields with associated streamlines. Near Post stall Regime Time averaged flow fields with associated streamlines. Angle of attack 15.8º, Re= 133333, U0=10 m/sAngle of attack 15.8º, Re= 133333, U0=10 m/s

Previous reserach on ehd excited airfoilsPrevious reserach on ehd excited airfoils

Near Post stall Regime Time averaged flow fields with Near Post stall Regime Time averaged flow fields with associated streamlines. associated streamlines.

Angle of attack 19.8º, Re= 333333, UAngle of attack 19.8º, Re= 333333, U00=25 m/s=25 m/s

Actuator off Actuator on

Electric forces: Electric forces: Through collisional process Through collisional process the force the force on the fundamental carriers becomes the force on the on the fundamental carriers becomes the force on the

mediummedium

n, m, n, m, and V represent the density number, the mass, the frequency of collisions and the and V represent the density number, the mass, the frequency of collisions and the relative velocity of the charged carriers to the medium macroscopic velocity (identifying relative velocity of the charged carriers to the medium macroscopic velocity (identifying positive ones with subindex + and negative ones with subindex -) positive ones with subindex + and negative ones with subindex -)

Neglecting both the magnetic effects and the interactions between charged Neglecting both the magnetic effects and the interactions between charged particles, and considering that the macroscopic force is an average of the forces particles, and considering that the macroscopic force is an average of the forces acting only on the heavy charge carriers (ions) of charge acting only on the heavy charge carriers (ions) of charge qq, the force transmitted to , the force transmitted to

the medium may be reduced to the coulombian force density expression:the medium may be reduced to the coulombian force density expression:

Alteration of physical properties of the gas (density, viscosity,..).

Electromechanical couplingElectromechanical coupling

VmnVmnF

EEqnqnF fcoul

Experimental set upExperimental set up

Airfoil model: NACA 0015

PMMA

Actuation

0.55<x/c<0.78

Power of Actuation <20W

Power/unit surface actuation<1000W/m2

Experimental set up: Wind tunnelExperimental set up: Wind tunnel

+HV-HV

Flow

Open wind tunnel of low Turbulence level

Test section: 450*450mm

Air stream: 0-7 m/s

Surface pressure measurements (micromanometer)

Flow visualization

(smoke injection and laser sheet)

20

0

.5,0 U

PPCp i

LayoutLayout

1.1. Low Reynolds Aerodynamic control.Low Reynolds Aerodynamic control.

2.2. EHD actuators.EHD actuators.

3.3. Electromechanical coupling.Electromechanical coupling.

4.4. Experimental setup.Experimental setup.

5.5. Results & discussion.Results & discussion. Laminar boundary layer :Laminar boundary layer :

Partially attachedPartially attached With separationWith separation

• Laminar boundary layer partially separatedLaminar boundary layer partially separated• Laminar boundary layer fully separatedLaminar boundary layer fully separated

Flow with a laminar separation bubble (LSB)Flow with a laminar separation bubble (LSB)• Fully reattached turbulent boundary layerFully reattached turbulent boundary layer• With downstream separation of the reattached turbulent boundary layerWith downstream separation of the reattached turbulent boundary layer

6.6. Conclusions.Conclusions.

Partially attached Partially attached Laminar boundary layerLaminar boundary layer

The plateu in the pressure is associated with flow separation

Separation occurs in the interelectrode space (x/c0.65 )

Wake mass deficit compensation

ActuationSeparation elimination

Laminar boundary layer partially Laminar boundary layer partially separatedseparated

FlowFlow

Flow separation upstream the actuator location

(x/c0.35 )

ActuationSeparation elimination

ActuationInviscid behaviour

Laminar boundary layer fully separatedLaminar boundary layer fully separated

Flow separation upstream the actuator location

(x/c 0.1 )

Actuation•Flow acceleration

•Intermitent reattachment

Flow with a laminar separation bubble (LSB)Flow with a laminar separation bubble (LSB)

Fully reattached turbulent boundary layerFully reattached turbulent boundary layer

Laminar separation bubble extended approximately from x/c = 0.1 to x/c = 0.5

ActuationSlight Flow acceleration of the attached flow

Actuation on an turbulent attached flow

(Large LBS)

Flow with laminar separation bubble (LSB)Flow with laminar separation bubble (LSB)

With downstream separation of the reattached With downstream separation of the reattached turbulent boundary layerturbulent boundary layer

ActuationVery Slight Flow acceleration of the separated flow

Laminar separation bubble approximately from x/c = 0 to x/c = 0.05 (analogue to a turbulator)Separation of turbulent boundary layer at x/c 0.15

Actuation on turbulent separated flow (Short LBS)

Difference on coefficients of aerodynamic performance as a consequence of EHD actuation

.

cbUL

WC

eleW

3

05.0

1

(º)

Re*10-4

FlowOn actuator

Cw Actuation Effect Cl

(off)

Cl Cl/CDp

(off)

(Cl/CDp)

0.0 4.4 Separated LBL (x/c≈0.65)

8.7 Reattacment - - - -

5.3 1.9 Separated LBL(x/c≈0.35)

101.2 Reattachment 0.20 0.21 11.9 5.82

11.5 1.9 Separated LBL(x/c≈0.10)

101.2 Intermitent reattachment

0.41 0.15 3.5 0.23

5.3 4.4 TBL (upstream Large LBS )

(x/c≈1)

8.7 Sligthacceleration of

the attached flow

0.44 0.03 17.3 -1.02

11.5 4.4 SeparatedTBL (upstreamShort LBS ) (x/c≈0.15)

8.7 Sligthacceleration of

the separated flow

0.62 0.03 4.5 -0.24

Actuator location 0.55<x/c<0.78

Non dimensional power coeffcient

Angle of attack

Lift coefficient

Lift and drag presssure ratio

ConclusionsConclusions

The relative distance between actuator and separation line The relative distance between actuator and separation line reveals a crucial parameter for low aerodynamics flow control. reveals a crucial parameter for low aerodynamics flow control.

Reattachment of the flow requires lesser power when Reattachment of the flow requires lesser power when separation occurs at close vicinity of the actuator, whatever separation occurs at close vicinity of the actuator, whatever the free airstream velocity.the free airstream velocity.

When separation occurs far upstream the actuation may be When separation occurs far upstream the actuation may be even not capable to reattach the flow, whatever the free even not capable to reattach the flow, whatever the free airstream velocity.airstream velocity.

The actuator activation on flows that did not experience The actuator activation on flows that did not experience separation close to the actuator does not produce a significant separation close to the actuator does not produce a significant improvement on the aerodynamics airfoil performance. improvement on the aerodynamics airfoil performance.

Merci beaucoup !!!Merci beaucoup !!!