Influence of Gravity and Lift on Particle Velocity Statistics and Deposition Rates in Turbulent Upwa

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Influence of Gravity and Lift onParticle
Velocity Statistics and Deposition Ratesin
Turbulent Upward/Downward Channel Flow
Workshop on Environmental Dispersion
Processes Lorentz Center University of Leiden
C. Marchioli, M. Picciotto and Alfredo Soldati
Dipartimento di Energetica e Macchine,
Università di Udine Centro Interdipartimentale
di Fluidodinamica e Idraulica Department of
Fluid Mechanics, International Center for
Mechanical Sciences, Udine
September, 18-27, 2006, Leiden, The Nederlands
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MotivationWhy the need for a DNS database?

• Lack of complete and homogeneous source of data
  on particle
• velocity statistics and on particle deposition
  rates (-gt)
• Validation and testing of theoretical deposition
  models

Free CFD database, kindly hosted by Cineca
supercomputing center (Bologna, Italy).
Over than 1 Tbyte DNS fluid-dynamics raw data for
different benchmark and test cases available on
line at
http//cfd.cineca.it/cfd
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CFD databaseWhats on?
1. CFD raw data repository (12 DB, 1.5 Tb)
DNS test case particle-laden turbulent channel
flow at low Reynolds number 2. CFD Preprocessed
data repository (2 DB) DNS database
influence of gravity and lift on
particle velocity statistics and deposition rates
http//cfd.cineca.it/cfd
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Numerical Methodology (1)Flow Field Calculation

• Time-dependent 3D turbulent gas flow field with
  pseudo-spectral DNS
• 128x128x129 Fourier-Fourier modes (1D FFT)
  Chebyschev coefficients
• Shear Reynolds number Retuth/n150
• Bulk Reynolds number Rebubh/n2100

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Numerical Methodology (2)Lagrangian Particle
Tracking
Equation of motion for the (heavy) particles

Stokes Number Sttp/tf Flow Time Scale
tfn/ut2
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Numerical Methodology (3)Lagrangian Particle
Tracking
Kolmogorov scales length scale 1.6 lt hk lt 3.6
(hk,avg 2) time scale 2.5 lt tk lt 13
(tk,avg 4)
Non-Dimensional Kolmogorov Time Scale, th, vs
Wall-Normal Coordinate, z
dp/hk O(1) In principle, it should be ltlt 1!
St/tk O(10)
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Numerical Methodology (4)Lagrangian Particle
Tracking

• Further Relevant Simulation Details
• Point-particle approach local flow distortion
  is assumed negligible (Stokes
• flow
  around the particle)
• One-way coupling dilute flow condition is
  assumed (NB the averaged mass
• fraction for the
  largest particles is O(0.1), however two-way
• coupling effects do
  not affect significantly particle statistics
• for the current
  simulation parameters).
• Particle-wall collisions fully elastic
  (particle position and velocity at impact
• and time
  of impact are recorded for post-processing!)
• Fluid velocity interpolation 6th-order
  Lagrangian polynomials
• Total tracking time ?T 1192 in wall time
  units i.e. 9.5 times the non-
• dimensional
  response time of the largest particles (St125).
• Time span during which statistics have been
  collected ?t 450 (from

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Part I. Influence of the Gravity ForceFlow
Configurations
No Gravity (G0) Downflow (Gd) Upflow (Gu)
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Part I. Influence of the Gravity ForceParticle
Mean Streamwise Velocity
Downflow
No Gravity
Upflow
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Part I. Influence of the Gravity ForceParticle
Wall-Normal Velocity
Downflow
Upflow
No Gravity
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Part I. Influence of the Gravity
ForceStreamwise RMS of Particle Velocity
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Part I. Influence of the Gravity
ForceWall-Normal RMS of Particle Velocity
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Part I. Influence of the Gravity
ForceWall-Normal Particle Number Density
Distribution (small St)
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Part I. Influence of the Gravity
ForceWall-Normal Particle Number Density
Distribution (large St)
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Part I. Influence of the Gravity ForceIntegral
Particle Number Density in the Viscous Sublayer
(zlt5)
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Part I. Influence of the Gravity ForceParticle
Deposition Rates Definition of the Deposition
Coefficient
Following Cousins Hewitt (1968)
Mass flux of particles at deposition surface
Mean bulk particle concentration
Non-Dimensional Deposition Coeff.
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Part I. Influence of the Gravity ForceParticle
Deposition Rates
Ref Young and Leeming, J. Fluid Mech., 340,
129-159 (1997) Marchioli et al., Int. J.
Multiphase Flow, in Press (2006).
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Part II. Influence of the Lift ForceMethodology
Lift Force Model

• Lift Coefficient

• Dimensionless Parameter

• References
• Mc Laughlin, J. Fluid Mech., 224,
  261-274 (1991)
• Kurose and Komori, J. Fluid Mech., 384,
  183-206 (1999).

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Part II. Influence of the Lift ForceParticle
Mean Streamwise Velocity (small St)
Downflow
No Gravity
Upflow
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Part II. Influence of the Lift ForceParticle
Mean Streamwise Velocity (large St)
Downflow
No Gravity
Upflow
With lift!
With lift!
With lift!
With lift!
With lift!
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Part II. Influence of the Lift ForceParticle
Wall-Normal Velocity (small St)
Downflow
No Gravity
Upflow
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Part II. Influence of the Lift ForceParticle
Wall-Normal Velocity (large St)
Downflow
No Gravity
Upflow
With lift!
With lift!
With lift!
With lift!
With lift!
With lift!
With lift!
With lift!
With lift!
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Part II. Influence of the Lift ForceWall-Normal
Particle Number Density Distribution (small St)
Downflow
No Gravity
Upflow
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Part II. Influence of the Lift ForceWall-Normal
Particle Number Density Distribution (large St)
Downflow
No Gravity
Upflow
With lift!
With lift!
With lift!
With lift!
With lift!
With lift!
With lift!
With lift!
With lift!
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Part II. Influence of the Lift ForceCoupling
between near-wall transfer mechanisms and lift
force
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Part II. Influence of the Lift ForceParticle
Deposition Rates
No Gravity
Downflow
St
St
Upflow
St
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Conclusions andFuture Developments

• We have quantified the effects of gravity and
  lift on particle
• velocity statistics and deposition rates in
  channel flow.
• Gravity modifies particle statistics via the
  crossing-trajectory
• effect, which decreases velocity correlations
  along the particle
• trajectories as the particle Stokes number
  increases (St 25
• being the threshold value to discriminate
  between small and
• large particles).
• Lift affects weakly the particles with Stgt25,
  whereas particles
• with St lt 25 will either increase or decrease
  their deposition
• rate depending on the orientation of gravity
  with respect to the
• mean flow.
• Gravity and lift seem to modify the particle
  statistics mostly
• quantitatively particle distribution is
  primarily a result of the
• dynamic interaction between particles and
  near-wall turbulence.
• Improve the lift force model