laboratory modeling of atmospheric dispersion at the fluid modeling facility of the u.s....
TRANSCRIPT
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Laboratory Modeling of Atmospheric Dispersionat the
Fluid Modeling Facilityof the
U.S. Environmental Protection Agency
byWilliam H. Snyder
MiniTech Presentation15 March 2006
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Meteorological Wind Tunnel
Test section: 3.7m wide, 2.1m high, 18.3 m longFree-stream speeds: 0.5 to 10 m/s.
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Water Channel / Towing Tank
Test section: 2.4m wide, 1.2m deep, 25m longTowing speeds: 1 to 50 cm/s.
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Convection Tank
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Block roughness
Honeycomb
Side view
Spires cut off
Perspective View – Spires & Block Roughness
Boundary-layer Generation Scheme
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0 .6 1.2 1.8 2.4 3 3.6 4.20
300
600
900
1200
1500
U, m/s
z, m
m
Cube Height
x, mm 8002 983111660153180.16 Power law
Mean Velocity Profiles
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Conc
Wind-tunnel demonstration of the influence of building width and height on the plume distribution in the wake.
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1
2
4
10
Variable:
Building Width in Crosswind Direction
Centerplane Streamlines
Observations
•Cavity length increases from 1.5h to 5.5h•Horseshoe vortex more prominent with wider buildings – reverse horseshoe vortex also observed downstream
•Most prominent effect is streamline lifting, but cavity height increases slowly with building width•2D Bldg should show closed streamlines in cavity
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Video-image, pseudo-color representation of concentration in building wakes. Instantaneous concentrations on left and long-term averages on right.
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Cubical Building Array
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Two-Dimensional Building Array
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WORLD TRADE CENTERSITE
FLOW
N
1:600 SCALE MODEL OF LOWER MANHATTAN
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Three Decades of Building Studies
• Contributions to the Scientific Understanding
• Rules of Thumb (“1 + 1½ times” rule for building-downwash prevention)
• Resulted in several Agency guidelines and regulations, including the guideline for performing Good Engineering Practice stack height analyses
• Provided the basis for the downwash algorithms in the ISCST and AERMOD models and the flow distortion algorithms in other applied models such as QUIC.
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Wind-tunnel study of plume downwash in complex terrain -- buoyant stack emissions from the Waste Technologies Industries municipal incinerator in East Liverpool, OH.
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Russian Hill Study: Streamline Patterns Derived from Wind-Tunnel Measurements over Three Idealized Hills with Maximum Slopes of 26o, 16o and 10o.
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Other Studies in Wind Tunnel
• Stack-tip downwash• Emissions from open-pit coal mines• Area sources• Roadways• Dense-gas studies• These studies have all resulted in improved algorithms in the Agency’s arsenal of applied dispersion models
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Tow Direction
Neutral Layer (fresh water)
Stratified Layer (w/ saltwater)
Static Density Gradient
Dye Plumes
Sampling Rake
∆zi
zi
Typical Setup in Towing Tank
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Plumes Released Above and Below the Dividing-Streamline Height
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Wind direction sensitivity of concentration pattern over Cinder Cone Butte in stable stratification in the towing tank.
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Wave Patterns & Ground-based Rotor
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Elevated Rotor
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Complex Terrain
• Wind-tunnel and towing-tank studies provided a strong foundation for the development and evaluation of the next generation of regulatory complex terrain models
• The concepts of the dividing streamline and stable plume impaction were demonstrated and refined
• Deflection of the height of the mixing layer by terrain
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Convection Tank
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Convection Tank
Fluorescent Dyes
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PLAN VIEW OF CONVECTION TANK WITH LASER SHEET LIGHTING
VIDEO CAMERA
LASER TABLE
SOURCE
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Laser-sheet Lighting System
Scanner mirror
Parabolic
Mirror
Argon-ion Laser Beam
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22 24 26 28 30 32 34 360
4
8
12
16
20
24
28
Temperature, oC
z, c
m
Before surface heating
6.8 min
14.8 min
Typical temperature profiles obtained during plume experiment. Timesare between commencement of heating and midpoints of traverses.
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Laser-illuminated buoyant plume in the convection tank
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and downwind distancesfor various plume buoyanciesPseudo-color images - mean concentration cross sections
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Puff Release Mechanism
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Average Concentration of Medium-Buoyancy Puff Release
t = 0.1 to 4 t*
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Dispersion in CBL
• Many features of original tank upgraded• Big advantage: ability to duplicate conditions• Buoyant plumes & puffs
• Penetrate into inversion• Gravity spreading in inversion layer• Eventually mixed down to the ground• Extreme "spottiness" in instantaneous views