Numerical simulation of scalar dispersion downstream of a square obstacle, Part II: Direct numerical simulations

A direct numerical simulation of scalar dispersion from a line source downstream of a square obstacle is performed using unstructured finite-volume schemes. The final goal of the analysis is an initial validation of the finite-volume technique for high-fidelity simulations of scalar dispersion in complex geometries, with a particular focus to the prediction of turbulent scalar fluxes. The scalar transport is approximated to a passive mechanism and the flow Schmidt number is limited to 10 in order to relax the computational cost dictated by the dissipative range of scalar fluctuations. The results clearly show that the scalar dispersion process is largely affected by the type of inflow condition adopted in the analysis, owing to the influence on the onset of transition in the wake behind the obstacle. However, the results also suggest that the numerical technique is able to give reliable predictions of mean scalar concentration and turbulent scalar fluxes when the inflow condition is properly specified