Particles%20in%20Turbulence

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Particles in Turbulence Preliminary results
from Lagrangian Acoustic Velocimetry
M. Bourgoin, P. N. Qureshi, A. Cartellier, Y.
Gagne, C. Baudet,
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Inertial particles in turbulence

• effect of particles finite size ?

• effect of particle to fluid density ratio ?

• effect of particles concentration (collective
  effects) ?

Preferential concentration - Clustering Enhancemen
t of settling velocity Dispersion
Lagrangian measurements to characterize
particles dynamics at large and small scales
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Outline

• Acoustic velocimetry technique

• principle of Acoustic Doppler velocimetry
• data acquisition and processing

•  Inertial  particles dynamics (preliminary)

• wind tunnel measurements
• finite size effects on velocity increments
  statitics

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Acoustic velocimetry principle
Ultrasonic Emitter
,
Receiver
Scattering vector
Doppler shift
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Acoustic velocimetry principle
L 50 cm
Ultrasonic Emitter
Ø 10 cm
,
100 kHz
160o
Receiver
Scattering vector
Doppler shift
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3D Acoustic velocimetry

• 4 independent projections

• Better SNR

• Well adapted for measurements
• in open flows with a (large) mean
• velocity

• Possibility for simultaneous
• Eulerian measurements (hot wire)

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Particles Gas filled soap bubbles
Inner gas
Using Hellium as inner gas, we can compensate the
weight of soap
Air
Neutrally buoyant particles
Soap
Air flow
D 2 - 6 mm
(Disp. lt 6 )
Air flow

• Adjustable parameters

• soap, gas and air flow rates
• inner gas type

Bubbles density, size and production rate
adjustable
Stokes number effects Lagrangian tracers ?
inertial particles
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Data Acquisition - Processing
Receiver
Complex downmixed signal
(90 kHz)
Emitter
Time-frequency analysis
a.u.
Time ms
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Inertial particles

• effect of particles finite size ?

• effect of particle to fluid density ratio ?

• effect of particles concentration (collective
  effects) ?

- Wind tunnel grid turbulence
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Inertial particles

• effect of particles finite size ?

• effect of particle to fluid density ratio ?

• effect of particles concentration (collective
  effects) ?

- Wind tunnel grid turbulence
- isolated neutrally buoyant particles
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Lagrangian velocity Increments statistics
2 mm bubbles
6 mm bubbles
PDF
PDF
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Lagrangian velocity Increments statistics
Lagrangian tracers in a
2 mm bubbles
6 mm bubbles
PDF
PDF
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Lagrangian velocity Increments statistics
Lagrangian tracers in a
2 mm bubbles
6 mm bubbles
PDF
PDF
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6
3
2 mm bubbles
2 mm bubbles
6 mm bubbles
6 mm bubbles
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Non-normalized acceleration PDFs
PDF
Acceleration a.u.
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Conclusions

• Acoustic Lagrangian Velocimetry technique (3D)

• Well suited for individual particle tracking in
  open flows
• Possibility of silmultaneous Eulerian
  measurements

• Tracking of soap bubbles inflated with gas

- density and size easily adjustable

• Size effects on large neutrally buoyant isolated
  particles (preliminary)

- Intermittency - weaker than for fluid tracers
- Smaller bubbles have larger acceleration
variance

• Surprisingly, we find a larger acceleration
  flatness for the
• larger bubbles

• Perspectives

• repeat the measurements for other sizes of
  bubbles

• heavy particles dynamics

• Clustering-Collective effects (many particles)

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Ultrasonic transducers
Sell-type transducers (electro-acoustical
circular piston)
Mylar sheet (15?m)
Zync plate
Ø 1 cm ? 30 cm

• Reciprocal

• Linear

200 V

• Large spectral band width

(20kHz ? 150 kHz)

• Directional

• Home made

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Data Acquisition - Processing
Receiver
Complex downmixed signal
(90 kHz)
Emitter
Time-frequency analysis
a.u.
Time a.u.
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Data Acquisition - Processing
Receiver
Complex downmixed signal
higher bubbles seeding density
(90 kHz)
Emitter
2 particles