Steady control of laminar separation over airfoils with plasma sheet actuators

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Steady control of laminar separation over
airfoils with plasma sheet actuators
Laboratorio de Fluidodinámica, Universidad de
Buenos Aires, CONICET, Buenos Aires, Argentina

• Sosa Roberto
• Artana Guillermo

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Introduction

• In last years there has been a growing interest
  in the use of ionization to add localized
  momentum to the flow by the collisions process of
  migrating charged particles with the neutral
  species of the air
• These EHD technologies have been considered as
  good candidates to enhance the aerodynamic
  perfomance of airfoils

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Objectives

• In this work we study the improvement of the
  aerodynamic performance of an airfoil at very low
  Re (Relt50000) by means of an EHD actuator
• Our study focuses on the relative distance of the
  actuator location and the position of separation
  line.

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Flow configurations at low Re aerodynamics
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
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Layout

• Interest.
• EHD actuators.
• Electromechanical coupling.
• Experimental setup.
• Results discussion.
• Laminar boundary layer
• Partially attached
• With separation
• Laminar boundary layer partially separated
• Laminar boundary layer fully separated
• Flow with a laminar separation bubble (LSB)
• Fully reattached turbulent boundary layer
• With downstream separation of the reattached
  turbulent boundary layer
• Conclusions.

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Some Area of Interest

• Power Control of Wind Turbines
• Wind turbines are usually designed to produce
  electrical energy with 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 energy of the wind in
  order to avoid damaging the wind turbine.
• Around two thirds of the wind turbines currently
  being installed in the world are stall controlled
  machines.
• The geometry of the fixed angle blades profiles
  is designed to 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 the rotor
• In practical application, stall control is not
  very accurate and many stall-controlled turbines
  do not meet their specifications. Deviations of
  the design-power in the order of tens of percent
  are regular

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Kind of ehd actuators

• Corona discharge.
• Dielectric barrier discharge.
• Sliding discharge.

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Previous research on ehd excited airfoils
Near Post stall Regime Time averaged flow fields
with associated streamlines. Angle of attack
15.8º, Re 133333, U010 m/s
Actuator off
Actuator on
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Previous reserach on ehd excited airfoils
Near Post stall Regime Time averaged flow fields with associated streamlines. Angle of attack 19.8º, Re 333333, U025 m/s
Actuator off
Actuator on
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Electromechanical coupling

• Electric forces Through collisional process the
  force on the fundamental carriers becomes the
  force on the medium
• n, m, ? 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 positive
  ones with subindex and negative ones with
  subindex -)
• Neglecting both the magnetic effects and the
  interactions between charged particles, and
  considering that the macroscopic force is an
  average of the forces acting only on the heavy
  charge carriers (ions) of charge q, the force
  transmitted to the medium may be reduced to the
  coulombian force density expression

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

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Experimental set up
Airfoil model NACA 0015 PMMA
Actuation 0.55ltx/clt0.78 Power of Actuation
lt20W Power/unit surface actuationlt1000W/m2
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Experimental set up Wind tunnel
Open wind tunnel of low Turbulence level Test
section 450450mm Air stream 0-7 m/s
Surface pressure measurements (micromanometer)
Flow visualization (smoke injection and laser
sheet)
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Layout

• Low Reynolds Aerodynamic control.
• EHD actuators.
• Electromechanical coupling.
• Experimental setup.
• Results discussion.
• Laminar boundary layer
• Partially attached
• With separation
• Laminar boundary layer partially separated
• Laminar boundary layer fully separated
• Flow with a laminar separation bubble (LSB)
• Fully reattached turbulent boundary layer
• With downstream separation of the reattached
  turbulent boundary layer
• Conclusions.

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Partially attached Laminar boundary layer
Separation occurs in the interelectrode space
(x/c?0.65 )
The plateu in the pressure is associated with
flow separation
Wake mass deficit compensation
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Laminar boundary layer partially separated
Flow
Flow separation upstream the actuator
location (x/c?0.35 )
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Laminar boundary layer fully separated
Flow separation upstream the actuator
location (x/c ? 0.1 )
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Flow with a laminar separation bubble (LSB)Fully
reattached turbulent boundary layer
Laminar separation bubble extended approximately
from x/c 0.1 to x/c 0.5
Actuation on an turbulent attached flow (Large
LBS)
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Flow with laminar separation bubble (LSB) With
downstream separation of the reattached turbulent
boundary layer
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)
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Difference on coefficients of aerodynamic
performance as a consequence of EHD actuation
Lift and drag presssure ratio
Actuator location 0.55ltx/clt0.78
Non dimensional power coeffcient
Angle of attack
Lift coefficient
? (º) Re 10-4 Flow On actuator Cw Actuation Effect Cl (off) ?Cl Cl/CDp (off) ?(Cl/CDp)
0.0 4.4 Separated LBL (x/c0.65) 8.7 Reattacment - - - -
5.3 1.9 Separated LBL (x/c0.35) 101.2 Reattachment 0.20 0.21 11.9 5.82
11.5 1.9 Separated LBL (x/c0.10) 101.2 Intermitent reattachment 0.41 0.15 3.5 0.23
5.3 4.4 TBL (upstream Large LBS ) (x/c1) 8.7 Sligth acceleration of the attached flow 0.44 0.03 17.3 -1.02
11.5 4.4 Separated TBL (upstream Short LBS ) (x/c0.15) 8.7 Sligth acceleration of the separated flow 0.62 0.03 4.5 -0.24
.
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Conclusions

• The relative distance between actuator and
  separation line reveals a crucial parameter for
  low aerodynamics flow control.
• Reattachment of the flow requires lesser power
  when separation occurs at close vicinity of the
  actuator, whatever the free airstream velocity.
• When separation occurs far upstream the actuation
  may be even not capable to reattach the flow,
  whatever the free airstream velocity.
• The actuator activation on flows that did not
  experience separation close to the actuator does
  not produce a significant improvement on the
  aerodynamics airfoil performance.

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• Merci beaucoup !!!