Local and urban scale modeling - Air Pollution Modeling and Its Application - page 11

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3. Questions and Answers
Steven Hanna: Do you think that the model could be improved by including a
parameterization scheme to increase the turbulence in the urban canopy and to
account for mesoscale meandering?
Answer: Including a urban-canopy parameterization might help, since at least in
the simulations presented for this case the calculated turbulence was lower than
the measured one. However, a specific parameterization has to go together both
with the turbulence closure and the boundary conditions around the obstacles,
thus it is not a trivial task to pursue. The mesoscale meandering definitely
cannot be simulated with the present setup of the model: we are considering a
single grid domain of 265 × 320 m 2 with a single input wind profile, thus the
mesoscale forcing is not solved. It should be remembered that the purpose of
the present study was to test if RAMS model is able, at all, to simulate the flow
at these scales and in the presence of obstacles. The next steps might be
focused in the direction pointed out in the question.
Bernard Fisher: The comment is often made that finescale features of buildings
have an important effect on flow and dispersion. Would the speaker like to
comment (especially in relation to the COST 732 study)?
Answer: This point was only partly a focus of the COST 732 Action, and it was
addressed by some participants using CFD (Computational Fluid Dynamics)
models. Since the evaluation of the importance of these effects was not con-
ducted in a fully systematic way, it is difficult to draw a generic conclusion. In
cases with a very complex geometry like in the Oklahoma City case, certain
finescale features of the buildings (e.g. garage openings) were found to have a
non negligible effect on the flow and dispersion. Again, this was a specific
example.