Scaling of building affected plume rise and dispersion in water channels and wind tunnels—Revisit of an old problem

The high cost and site-specific results of field experiments have made water channels and wind tunnels important tools for the investigation of urban air quality. However, the applicability of laboratory studies depends on the correct scaling of the dominant physical properties. Simulation of the urban dispersion problems in laboratory facilities requires correct scaling of mean flow, plume rise, and turbulence governed plume spread. In this paper, a method for scaling the urban dispersion parameters in water channels and wind tunnels is presented. This method has been previously proposed and studied for the plume rise from isolated stacks; however, it has not been evaluated for cases of plume rise affected by surrounding buildings. Water channel experiments show that plume rise associated with relatively low-level buoyant sources in urban areas is highly affected by the complex flows induced by surrounding buildings, an effect which current plume rise models are not able to accurately reproduce. Based on these experiments, a new method for calculating the plume rise in urban areas, which accounts for the effect of surrounding buildings, is developed. The similarity of flow and plume rise, by matching the densimetric Froude number and relaxing initial density condition at the source, enables correct scaling of the concentration measurements from the laboratory to the field through the non-dimensional Gaussian dispersion model. This technique allows us to investigate the dispersion of buoyant emissions from low-level sources in urban areas through water channel or wind tunnel simulations. The sensitivity of this scaling technique under specific urban conditions is investigated.