Presentation on theme: "Laboratory Modeling of Atmospheric Dispersion at the Fluid Modeling Facility of the U.S. Environmental Protection Agency by William H. Snyder MiniTech."— Presentation transcript:
Laboratory Modeling of Atmospheric Dispersion at the Fluid Modeling Facility of the U.S. Environmental Protection Agency by William H. Snyder MiniTech Presentation 15 March 2006
Meteorological Wind Tunnel Test section: 3.7m wide, 2.1m high, 18.3 m long Free-stream speeds: 0.5 to 10 m/s.
Water Channel / Towing Tank Test section: 2.4m wide, 1.2m deep, 25m long Towing speeds: 1 to 50 cm/s.
Block roughness Honeycomb Side view Spires cut off Perspective View – Spires & Block Roughness Boundary-layer Generation Scheme
Mean Velocity Profiles
Conc Wind-tunnel demonstration of the influence of building width and height on the plume distribution in the wake.
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
Video-image, pseudo-color representation of concentration in building wakes. Instantaneous concentrations on left and long-term averages on right.
Cubical Building Array
Two-Dimensional Building Array
WORLD TRADE CENTER SITE FLOW N 1:600 SCALE MODEL OF LOWER MANHATTAN
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.
Wind-tunnel study of plume downwash in complex terrain -- buoyant stack emissions from the Waste Technologies Industries municipal incinerator in East Liverpool, OH.
Russian Hill Study: Streamline Patterns Derived from Wind-Tunnel Measurements over Three Idealized Hills with Maximum Slopes of 26 o, 16 o and 10 o.
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 Agencys arsenal of applied dispersion models
Tow Direction Neutral Layer (fresh water) Stratified Layer (w/ saltwater) Static Density Gradien t Dye Plumes Sampling Rake zizi zizi Typical Setup in Towing Tank
Plumes Released Above and Below the Dividing-Streamline Height
Wind direction sensitivity of concentration pattern over Cinder Cone Butte in stable stratification in the towing tank.
Wave Patterns & Ground-based Rotor
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
PLAN VIEW OF CONVECTION TANK WITH LASER SHEET LIGHTING VIDEO CAMERA LASER TABLE SOURCE
Temperature, o C z, cm Before surface heating 6.8 min 14.8 min Typical temperature profiles obtained during plume experiment. Times are between commencement of heating and midpoints of traverses.
Laser-illuminated buoyant plume in the convection tank
and downwind distances for various plume buoyancies Pseudo-color images - mean concentration cross sections
Puff Release Mechanism
Average Concentration of Medium-Buoyancy Puff Release t = 0.1 to 4 t*
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