Direct Measurement of Particle Behavior in the Particle-Lagrangian Reference Frame of a Turbulent Flow

1
Direct Measurement of Particle Behavior in the
Particle-Lagrangian Reference Frame of a
Turbulent Flow

• James A. Bickford
• M.S.M.E. Defense
• 10 August 1999
• Advisor Chris Rogers (Tufts University)
• Committee Members Vincent Manno (Tufts
  University)
• Martin Maxey (Brown University)

2
Outline

• Overview and Applications
• Quasi-numerical Simulation
• QNS Method
• Velocity autocorrelations, spectra
• Integral scales
• u
• Anomalous drift
• Digital Particle Image Velocimetry
• DPIV Method
• Kolmogorov estimates
• Effects of preferential concentration

3
Particles and Turbulence

• Turbulent Fluid Fluctuations
• Occur on a range of length and time scales
• Suspended particles respond to these scales

4
Applications

• Engine combustion, radiation and pollution
  control, volcanic erruptions
• Aeolian Martian processes
• Formation of planetary bodies and large scale
  structure of the universe

5
Three-tiered research approach

• Tactical approach uses separate but complimentary
  methods
• Microgravity flight experiments
• Direct numerical simulations
• Quasi-numerical simulations

6
Quasi-Numerical Overview

• Technique
• Hybrid numerical-experimental
• Two-axis traverse emulates a virtual particle in
  a water flow
• Measures turbulence statistics in the particles
  reference frame
• Variable Parameters
• Particle time constant
• (size)
• Drift velocity
• (gravity)
• Reynolds number
• (turbulence intensity)
• Data Acquisition Methods
• Laser Doppler Velocimetry
• Digital Particle Image Velocimetry

7
QNS Methodology
Read Fluid Velocity
Repeat gtgt Tk
Update Traverse Velocity
8
Particle Response to Turbulence
Velocity
Particle Velocity
Fluid Velocity (along particle path)
Velocity
Velocity
Time
Time
9
Movie - QNS in action
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Effect of Gravity on Velocity Autocorrelations

• Gravity
• Decreases Correlation times
• crossing trajectories effect
• Increases relative particle energy at higher
  frequencies
• Little effect on fluid spectra

Rii / u2
Time
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Effect of Particle Inertia on Velocity
Autocorrelations

• Particle Inertia
• Increases particle correlation times
• Almost no effect on fluid correlations or
  spectra
• Decreases relative energy at higher frequencies

Rii / u2
Time
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Effect of Gravity on Integral Scales

• Gravity
• Fluid Scales Decrease
• Streamwise
• Streamnormal (more)
• Particle Scales
• Possible decrease (tiny)
• p-L fluid scales
• ME pL _at_ Sg 1

T2p-L / T2me
Sg
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Effect of Particle Inertia on Integral Scales

• Inertia
• General increase in fluid and particle integral
  scales
• Possible local peaks
• Tf 1 (particle)
• Tf 0.7 (fluid)
• SW more prominent

T1p-L / T1me
Stme
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Anomalous Drift Velocities
(Measured Drift - Imposed Drift) / U
Stme
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U Dependence on Gravity and Particle Inertia
Streamwise
Streamnormal
Uipl / Uime
Stme
Stme
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Mechanisms Dictating Particle Behavior

• Looking beyond single point statistics
• Vorticity as a governing force for particle
  motion
• Preferential concentration

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Digital Particle Image Velocimetry

• Four computers used during simultaneous QNS
• Master control
• Traverse control (DSP)
• Frame grabber
• Laser and camera pulse control
• 750 mW pulsed diode laser illuminates a 2-D plane
  of the flow
• Dichroic filter allows camera and LDV regions to
  coincide
• Kodak ES-1 camera grabs 1008x1018 pixel images at
  30 Hz

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Image Correlations

• Images broken into sections (interrogation
  windows)
• Sub-images cross-correlated to produce vector
  field

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Bad Vector Identification

• Bad correlations (lighting, dirt, 3-D effects)
• Bad vectors are identified by comparing the
  velocity of a given vector to its surrounding
  neighbors.

? 2 (good)
? 2 (good)
? 8 (bad)
? 6 (bad)
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Tagged Vector Replacement

• Average with surrounding vectors
• iterate to fix coincident vectors
• inaccurate velocities
• reduced resolution
• Replace with higher order interpolated value
• more accurate interpolation
• same reduced resolution
• Use secondary correlation peaks
• no loss of resolution or accuracy

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Estimation of the Kolmogorov Fluid Time Scale

• Kolmogorov Fluid Time Scale

• Results

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Effect of Preferential Concentration on Particle
Path
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Conclusion

• Gravity and Inertia
• Affect particle trajectory which in turns affects
• Integral scales
• Measured u
• Measured vorticity
• Observed Anomalies
• Drift
• Integral scale dependence

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Acknowledgements

• Committee Members
• Chris Rogers
• Vincent Manno
• Martin Maxey
• Staff
• Jim Hoffmann, Vinny Maraglia
• Audrey-Beth Stein, Joan Kern
• TUFTL
• Becca Macmaster, AJ Bettencourt
• Dave McAndrew, Dan Groszmann, Scott Coppen, Jon
  Coppeta, Merre Portsmore

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Ainley Bickford Rii Comparisons

• Fluid Velocity Autocorrelation

• Particle Velocity Autocorrelation