EXPERIMENTAL INVESTIGATION OF BOUNDARY LAYER TURBULENCE IN A WATER FLUME Daniel E. Dombroski PI:...
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Transcript of EXPERIMENTAL INVESTIGATION OF BOUNDARY LAYER TURBULENCE IN A WATER FLUME Daniel E. Dombroski PI:...
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
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
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
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
ADV Significantly Underreports Turbulence Statistics
Spalart DNS (1988)
Biofouling
Early Stage
Fouling Plate
Early Stage
Fouling Plate
Late Stage
Fouling Plate
Late Stage
Fouling Plate
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,
τ 50 Stress
Calculation
τ 50 Stress
Calculation
Ship Wake Wind Chop
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
3D PLIF Schematic
Flow Dynamics
QuickTime™ and aNone decompressor
are needed to see this picture.
Coherence
QuickTime™ and aNone decompressor
are needed to see this picture.
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)
time
“Burst – Sweep” Action
Moving away from the plume centerline…
Scalar Gradients(ie, where’s the mixing?)
dC/dx dC/dy
dC/dz
Correcting Artifacts
Spatial Undersampling