| Summary: | 碩士 === 淡江大學 === 水資源及環境工程所 === 83 === The flow field and diffusion phenomena over complex terrain is
affected by topography. A series of experiments were conduced
to measure the flow field and diffusion variations near
a two-dimensional triangular ridge at the
Atmospheric Environmental Wind Tunnel in Tamkang
University. The methane (CH4) was used as the tracer in these
experiments and released from a stack which was located
upwind of the ridge. The main purpose is to investigate
the effects of a ridge on the diffusion and transport
under different actual stack heights. In order to discuss
the differences between disturbed and undisturbed
conditions, the experiment without ridge was also measured
for comparing. In this experimental study, a 1:1000 scale
mountain was used. On this scale the wind tunnel boundary
layer represents a 600m deep atmospheric boundary layer.
The estimated model surface roughness length (0.286mm)
represents 28.6 cm in the real field, which corresponds
to that typical flow over vegetated area. The velocity and
turbulence data were obtained with constant-temperature hot-
film anemometer with a x-array end-flow type hot-film probe.
The neutral buoyant methane tracer gas was released through a
copper tube with 5mm inside diameter. The concentration 65
were measured by a Hydrocarbon Analyzer, which is a flame
ionization detector (FID). The resulting velocity fields as
well as concentration fields are shown that they are highly
depended on the slope of the ridge. The fluctuating velocity
is increased proportional to the slope of the ridge. When the
source is located upwind of the ridge, the resulted ground-
level concentration will be lower because of the higher
level turbulence intensity and the upward streamline.
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