Subgrid particle resolution for the turbulent transport of a passive scalar

The transport of passive scalar in turbulent flows remains a challenging and important problem for several reasons. First, the passive scalar spectra exhibit various behaviors depending on the molecular Schmidt number value (see [3]). The passive scalar spectrum with a high Schmidt number exhibits thus a k−1 scaling between the Kolmogorov scale and the Batchelor scale [1]. This suggests that it is more demanding in terms of spatial resolution than the momentum. Moreover, capturing accurately advected scalar quantities is of crucial important in reacting flows, as concentrations controls reaction rates [5]. In Large Eddy Simulations, classical subgrid-scale models, which only focus on dissipation related to the transfer of energy to small scales, are not sufficient to predict adequately the effect of non-resolved small scales of the advected concentrations on the large scales involved in the reactions. Another field where passive scalar requires special care is the case of free surface multiphase flows when interfaces and surface tensions are captured by a level set method. The idea of using a different resolution for the scalar ad the momentum is therefore natural. This paper investigates the use of a subgrid particle methods to predict accurately small scales while keeping the computational cost at a reasonable level.