Effects of Reynolds number on stack plume trajectories simulated with small scale models in a wind tunnel

An analysis of the effect of Reynolds number on plume trajectories simulated at small scale in a wind tunnel is presented. Results demonstrate that the Reynolds number of flow leaving the stack (Re)D could be critical in specific simulations. In the case studied, when (Re)D is around 2196 the exit velocity profile in the cylindrical stack is distorted relative to full scale, or high model (Re)D scenarios (i.e. (Re)D>3000(Re)D>3000), increasing the momentum flux in plume, thus increasing the height of the plume. The overestimation of plume rise leads to underestimation of ground level concentrations; therefore the simulation will not be conservative if used for environmental impact assessment purposes. The analysis shows that the effect of (Re)D is mainly due to the shape of the emission velocity profile and implies that the details of the turbulent structure of the releases are not important. This is likely because the turbulence in the plume is dominated by internally generated turbulence that originates from the initial interaction with the cross-flow. Results indicate that measurements of the exit velocity profile and the use of the Briggs generalised plume rise theory can furnish a reliable estimate of the errors in plume rise induced by (Re)D in specific wind tunnel simulations.