Wednesday, 22 May 2002
Near surface atmospheric plume dispersion through a compact cylinder array
Detailed experiments of near-field plume dispersion through a uniform
array of cylindrical barrels were conducted on the salt flats of
Utah's Western Desert. A 5 x 9 rectangular array of 45 barrels,
height H=0.91 m and diameter d=0.57 m, was constructed with a barrel
spacing of 1.8 m, center to center. Propylene tracer gas was released
through a 25.4 mm diameter pipe, both upstream and within the barrel
array. The dissemination rate was fixed at 15 slm using a mass flow
controller. The tracer source was located at both ground level and 1H.
At each of the two source heights, four different barrel configurations
were arranged near the source. In the first and second configurations,
the source was located directly upwind of a single barrel and two barrels
placed side by side, respectively. In the third configuration the source
was surrounded by four barrels. In the final configuration the source
was located directly upwind of a three barrel pyramid. Instantaneous
concentration measurements were simultaneously acquired within the array
from 40 photoionization detectors arranged in three, 50 degree arcs.
Turbulence data in the roughness sub layer and near the source were also
measured using 3-6, three dimensional sonic anemometers. Overall,
13.5 hours of data were collected spanning 4 days.
Atmospheric stability during the experiments ranged between
-0.8 < z < 0.4, where z denotes the Monin-Obukhov stability
parameter as calculated from a sonic anemometer located at a height
of 3.2 m. Results include statistical profiles, distributions, and
intermittency factors of the concentration within the array as a
function of source configuration and atmospheric stability. Results
from the study will benefit both the physical understanding of near-field
plume behavior in the presence of surface mounted obstacles as well as
the development of Lagrangian stochastic models used to predict dispersion
in urban environments.
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