Environmental Engineering Reference
In-Depth Information
outside the y-bounds of the barrier that edge effects became more of a factor. In
summary, the barrier proved to be long enough that several sampler locations
on each crosswind sampling line in the direct downwind influence of the
barrier did not show edge effects. The next step is to knit the concentration
fields together to produce a result that would be expected from an infinitely
long barrier. Our EPA colleagues demonstrated this technique in the wind
tunnel study report.
Peter Builtjes:
The effect found of the barrier is larger than I recall from CFD
calculations. What is your experience with that?
Answer:
The decreases in tracer concentration we measured behind the barrier
were in the upper range of decreases reported in previous field studies, which
was typically 50-60%. In some of our individual experiments we observed
decreases greater than that although this was often associated with clear edge
effects. We commonly observed decreases of 50-60% even when there was
little evidence of any significant edge effects. The EPA wind tunnel results
were also similar to our results. Therefore, it seems reasonable to conclude that
the tracer concentrations from our field study are accurate.
Clemens Mensink:
Some CFD models do show an increase of concentrations in
the vertical direction behind the barrier. Do you have any information on the
concentration distribution in the vertical direction?
Answer:
We desired to investigate the tracer concentration distribution in the
vertical direction, but were limited by funding constraints to only ground-level
concentrations, i.e., 1.5 m AGL.