DNS and RANS Simulation of Dispersion Downstream of an Obstacle

摘要

Dispersion in the wake of an obstacle is studied as a step towards the analysis of bio-agent release in urban environments. Available experimental measurements are used to compare in details numerical predictions obtained using Reynolds-Averaged Navier-Stokes (RANS) techniques and Direct Numerical Simulations (DNS). In particular, turbulent scalar fluxes are compared to assess the quality of simple closure based on eddy diffusivity assumptions. The results obtained using different RANS closures show considerable spread in the results, with satisfactory agreement obtained by one model which predicts very low levels of turbulence in the obstacle wake. On the other hand, DNS is fairly accurate but very sensitive to adopted inflow conditions. Finally, in terms of the turbulent fluxes the RANS models qualitatively represent the vertical flux but fail to predict the streamwise components while DNS predictions, at least for the highest Reynolds number considered, represent both components with a fairly good level of accuracy.