The effects of unresolved scalar fluctuations during homogeneous nucleation

The effects of the subgrid-scale (SGS) scalar interactions on nanoparticle nucleation are investigated via a priori analysis of direct numerical simulation data. The formation of dibutyl-phthalate (DBP) particles via homogeneous nucleation is simulated in a planar wake. Classical nucleation theory is used to model particle nucleation and the Navier-Stokes equations are coupled with the scalar transport equations to provide the fluid, thermal, and chemical fields. The data shows that particle nucleation is initially confined to the thin interfacial region or shear layers, where molecular diffusion is dominant. As the flow becomes turbulent nucleation increases significantly and the rate of particle formation increases by several orders of magnitude. To assess the effect of SGS scalar interactions on DBP particle nucleation, the temperature and massfractions are filtered and the resulting quantities are used to compute the nucleating particle field. Two filter widths are used to obtain varying levels of SGS interactions. Particle size distributions are computed to examine the particle fields produced. This work shows that the SGS interactions' effect on nucleation has two distinct trends. In the proximal region of the wake, the unresolved interactions act to decrease particle formation. However, as the flow transitions or becomes turbulent the effect of the SGS interactions act to increase particle formation.