MUST

The Mock Urban Setting Test experiment is a near urban scale tracer dispersion experiment. In urban areas dominates a turbulent flow, affected by the building geometry. Because of that MUST uses turbulent inflow generation and dynamic Smagorinsky model.
The Research of gas dispersion in urban environment is, especially for pollutant gases by traffic etc., important for assessments of possible health damage.
There are difficulties in measuring and understanding occurred structures and there impact on pollutant gas dispersion. Large eddy simulation models help finding fundamental knowledge. The All Scale Atmospheric Model ASAM is used to simulate tracer gas dispersion events in urban area with building resolving resolution. The comparison with experimental data is used to evaluate the LES model.

Fig.7: Tracer gas plume with linear opacity of concentration values.

ASAM simulation results show flow structures like increased wind speed due to channelling affects in a narrow street canyon or wake flow regions with recirculation like we expect in urban areas. The good agreement between simulation (green color) and field experimental (blue color) data of wind speed (Fig. 7a at centre tower CT) and concentration time series (Fig. 7b at two different measurement locations) and mean vertical profile concentration (Fig. 7c at CT and south west tower SWT) are shown inside Fig. 7, where the tracer gas plume is pictured. The focus lie on extrema – wind gust and peak concentration values. In fact at both variables, the magnitudes of peaks and their frequency of occurrence are comparable to field measurements.

In the following Video you can see the distribution of a tracer gas inside a block of houses. Beside the spatial distribution it’s also shown the vertical distribution of the tracer.