turbulence effects on particle dispersion in a free-surface flow salvatore lovecchio, cristian...
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Turbulence effects on particle dispersion in
a free-surface flowSalvatore Lovecchio, Cristian Marchioli, Alfredo Soldati
Università degli Studi di Udine
Dipartimento di Ingegneria Elettrica Gestionale e Meccanica
Oceanographical applications
Settling of organic and inorganic matter
Dispersion of drifters or floaters
Motion of phytoplankton
Motivation
Outline of the Presentation
• Physical Problem and Modelling Approach
• Part 1: Flow at surface
• 1.1 Energy spectra• 1.2 Structures at surface
• Part 2: Particles segregation
• 2.1 Surface divergence
• 2.2 Intermittency in clustering• 2.3 Time scales
• Conclusions and future developments
Physical Problem andModelling Approach
• 3D turbulent water flow field at shear Reynolds number: Re= 171, 509• Channel size: Lx x Ly x Lz = 4 h x 2 h x 2h• Pseudo-spectral DNS: Fourier modes (1D FFT) in the homogeneous directions (x and y),
Chebyschev coefficients in the wall-normal direction (z)• Time intergration: Adams-Bashforth (convective terms), Crank-Nicolson (viscous
terms)
Free-slip wall
No-slip wall
Physical Problem andModelling Approach
Free-slip wall
No-slip wall
• 3D turbulent water flow field at shear Reynolds number: Re=171, 510• Channel size: Lx x Ly x Lz = 4 h x 2 h x 2h• Pseudo-spectral DNS: Fourier modes (1D FFT) in the homogeneous directions (x and y),
Chebyschev coefficients in the wall-normal direction (z)• Time intergration: Adams-Bashforth (convective terms), Crank-Nicolson (viscous
terms)
Physical Problem andModelling Approach
Physical Problem andModelling Approach
1. Flow at surface
Komori et al. : [...] Large fraction of the Near-wall burtsting events result in surface renewal events [...] JFM (1989)
1. Flow at surface
Streamwise energy spectrum of the streamwise velocity
Komori et al. : [...] Large fraction of the Near-wall burtsting events result in surface renewal events [...] JFM (1989)
Streamwise energy spectrum of the spanwise velocity
1. Flow at surface
Komori et al. : [...] Large fraction of the Near-wall burtsting events result in surface renewal events [...] JFM (1989)
2. Particles segregation
2. Particles segregation
x+ x+
y+
y+
∇ 2D ∇ 2D
Clustering is intermittent
3. Surface cluster renewal
Intermittency is due to
near-bottom turbulence
Upwellings
∇ 2D
x +
y+
Clustering is intermittent
3. Surface cluster renewal
Intermittency is due to
near-bottom turbulence
Upwellings
∇ 2D
x
y+
Lagrangian time scale:
3. Cluster renewalFlow time scale
Structures at Surfacepersiste for long time!!
3. Correlation DimensionFractal dimension of cluster
3. Correlation DimensionFractal dimension of cluster
Particles distributeduniformly over surface:
3. Correlation DimensionFractal dimension of cluster
Particles distributeduniformly over surface:uniformly into a line:
3. Correlation DimensionFractal dimension of cluster
Particles distributeduniformly over surface:uniformly into a line:
Generally:
3. Correlation DimensionFractal dimension of cluster
3. Correlation DimensionFractal dimension of cluster
3. Forcing at surface: the effect ofwind
A:WIND opposite the direction of flow
AMean streamwise velocity
3. Forcing at surface: the effect ofwind
B:WIND in the same direction of flow
BMean streamwise velocity
4. Conclusion and Future Developments
It was perfomed DNS of open channel flow at Re =171 e Re=509
Flow at surface was characterised by energy spectra and lagrangian time scale (LTS)
Particles tend to cluster into fractal structures with correlation dimension less than one
The segregation at surface is intermittent (cluster surface renewal) due to bursts of bottom layer turbulence and cluster have life-time greater than LTS
Thank you for your
kind attention