experimental investigation of boundary layer turbulence in a water flume daniel e. dombroski pi:...
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EXPERIMENTAL INVESTIGATION OF BOUNDARY LAYER TURBULENCE IN A
WATER FLUME
Daniel E. DombroskiPI: John P. Crimaldi
Environmental Fluid Mechanics Laboratory, University of Colorado at Boulder
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Some Background
• pollutants
• odor signals
• reproduction
Environmental Fluid Mechanics:
- Implications of Turbulence on Natural Systems- Duality of Hydrodynamics and Chemical Signaling- Methodology & Devolopment of Techniques
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Projects• Accuracy of Acoustic Doppler Velocimetry
(ADV) Measurements in Turbulent Boundary Layer Flows*
*Dombroski and Crimaldi, Limnology & Oceanography: Methods, 2007
• Biofouling Phenomena: Growth of communities of organisms on submerged surfaces
• 3D Visualization of Plume Dynamics
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Accuracy of Acoustic Doppler Velocimetry
Acoustic Doppler Velocimeter
- Commonly Used Field Instrument- ‘Economical’ ~ $10k- Relatively Low Spatio-Temp Resolution
Laser Doppler Velocimeter
- Precision Laboratory Instrument- ‘Pricey’ ~ $250k +- High Spatio-Temp Resolution
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ADV Significantly Underreports Turbulence Statistics
Spalart DNS (1988)
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Biofouling
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Early Stage
Fouling Plate
Early Stage
Fouling Plate
Late Stage
Fouling Plate
Late Stage
Fouling Plate
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AlgorithmStatistical analysis of stress lulls in
instantaneous record
AlgorithmStatistical analysis of stress lulls in
instantaneous record
01
1),(tt
tP
M
ii
acritA −=∑=
ψτ
aiai
ai
tLtLtLi≥−<= if
if 0{ψ
∑=
Δ=max
)(N
jjii
a
tjHψ
Steps:(1) Calculate stress record, τ =u’w’(2)Divide record into stress ‘lulls’, Li
(3)Calculate anchoring probability, Pa:QuickTime™ and a
TIFF (Uncompressed) decompressorare needed to see this picture.
Figure adapted from Crimaldi et al, 2002
Dependent on criteria Tcrit & ta
where
For discrete time intervals Δt, evaluate ψi as:
Where ja = # of time steps in ta
i
i
NjNji jH <≤
≥= 1 if if
10 {)( where Ni = # of samples in
ith stress lull∑∑= =−
Δ=
max
11
)(),(N
jj
M
ii
pacritA
a
jHtt
ttP τ
Nmax = # of samples in longest stress lull
Combining,
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τ 50 Stress
Calculation
τ 50 Stress
Calculation
Ship Wake Wind Chop
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Flow Visualization3D Planar Laser Induced Fluorescence
• Scalar: Rhodamine 6GPassive - Moves with and diffuses relative to the flow
without effecting the governing physicsConservative - Nonreactive
• Plume: Bed-level, low momentum release– Think odor release at river bed
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3D PLIF Schematic
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Flow Dynamics
QuickTime™ and aNone decompressor
are needed to see this picture.
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Coherence
QuickTime™ and aNone decompressor
are needed to see this picture.
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Relevant Scales
• Experimental Resolution• Image Plane (based on CCD chip) ~ 0.1 mm• Transverse (based on laser beam) ~ 0.25 mm
• Kolmogorov - smallest eddies~ 1 mm
(Estimated from dissipative & viscous scaling)
• Batchelor - smallest chemical gradients
~ 0.01 mm (Estimated from Kolmogorov scale, Schmidt number)
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time
“Burst – Sweep” Action
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Moving away from the plume centerline…
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Scalar Gradients(ie, where’s the mixing?)
dC/dx dC/dy
dC/dz
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Correcting Artifacts
Spatial Undersampling