A SEMIEMPIRCAL MODEL TO CALCULATE THE DIS PERSION OF GROUND-LEVEL RELEASES WITHIN STRUCTURED BUILDING ARRANGEMENTS

As a combination of wind tunnel and calculated data, semiempirical mod els predict the dispersion of ground level releases within built-up ar eas. The following example of such a semiempirical model describes an application for point sources and releases of neutral density. Two par ameters of that model are the so-called radius of homogenization and t he lateral shift of the dispersion plume in the case of an oblique app roach flow to the main orientation of the buildings. Both were determi ned by wind tunnel experiments using a variety of arrangements of buil dings. Comparing the results of the semiempirical model with other win d tunnel results and on-site data, a better forecast of the concentrat ion as with Gaussian Plume Models can be discovered. Normally, GPM do not include influences of the building arrangement on the dispersion l ike for instance the lateral shift of the plume. With the available da ta of the wind tunnel and the semiempirical model one is able to repro duce such effects without a considerable increasing of the arithmetic expenditure in comparison with the unmodified GPM.