Abstracts - KTH Mechanics

Validation of urban dispersion simulations by comparison of
simulations and measurements obtained around 2D and 3D
building arrays in a wind tunnel
O. Parmhed ∗ , and G. Patnaik †
The recent evolution in computer power has made it possible to perform Large
Eddy Simulations (LES) for complex gemotries like e.g. submarine hydrodynamics 1 .
Among the present uses is the simulation of urban dispersion of airborne hazardous
materials. Such material may be accidentally released in e.g. accidents with transport
of industrial chemicals or deliberately released by e.g. terrorists. As an example,
Figure 1(a) shows the simulated concentration of some pollutant five minutes after
an instantaneous release (bomb) in the Stocholm Old Town.
Although important, validation of such simulations is difficult. In this study we
compare simulations to observations of the flow around building arrays in a windtunnel.
As opposed to the case of the single building, there have been relatively fewer
measurement campaigns of the flow around groups of buildings. For this reason, and
to provide a data set suitable for the validation of Computational Fluid Dynamics
(CFD) codes, Brown et al 2 conducted experiments of 2D and 3D building arrays in
the U.S. Environmental Protection Agency’s (USEPA) Fluid Modeling Facility wind
tunnel. The building arrays consist of 7 or 7x11 rectangular blocks. Figure 1(b) shows
the setup for the 3D case.
Here we present results from CFD simulations using LES. The simulations have
been performed with various models for subgrid turbulence and with and without wall
models. Two different CFD codes have been used, FOAM and Fast3D. We present
here comparisons with both these codes and the measurements from the wind tunnel,
Figure 1(c). In general, satisfactory results are obtained.
∗ FOI, Swedish defence research agency, Grindsjön Research Centre, SE - 147 25 Tumba, Sweden
† NRL, Navy Research Laboratory, Washington, DC 20375-5344, USA
1 Grinstein and Fureby, Comp. Sci. Eng. 6, 37 (2004)
2 Brown et al., Int. Soc. Environ. Hydraulics, Tempe, AZ, 6 (2001)
(a) (b) (c)
Figure 1: Simulated dispersion in the Stockholm old town (a). Along flow velocity in
windtunnel validation simulation (b). Comparison of profiles (c).
181