The effects of turbulence on nanoparticle growth in turbulent reacting jets

Abstract

The effects of turbulence on nanoparticle growth in turbulent reacting flows are studied via a priori analysis of direct numerical simulation data. The formation and growth of titanium dioxide nanoparticles in incompressible planar jets are simulated via gas-phase hydrolysis of titanium tetrachloride. The particle field is captured by utilizing a nodal approach which accounts for nucleation, condensation, and Brownian coagulation. Simulations are performed at a single Reynolds number and two different precursor concentration levels. Instantaneous, filtered, and averaged data are presented to convey the nature of turbulent or unresolved contributions to the growth of nanoparticles. The effects of turbulence on particle dynamics, in the context of both Reynolds-averaged Navier–Stokes simulation and large-eddy simulation, are assessed by comparing the exact, turbulent, and subgrid-scale growth rates. The results show that large particles are produced in the regions away from the jet core, and an increase in the precursor concentration level increases the particle mean diameter. Particles grow faster when the precursor concentration is increased. It is further observed that the growth rate of the particles is higher inside the eddies and it increases as the jet grows. Additionally, the results show that the unresolved small-scale fluctuations can both augment and inhibit particle growth. However the predominant effect is to reduce particle growth. This tendency is increased (in magnitude) as the precursor concentration level is increased.