Effects of LES sub‐grid flow structure on particle deposition in a plane channel with a ribbed wall

Abstract

AbstractTransport and deposition of aerosol particles in a plane channel with a ribbed wall are studied in order to investigate the effects of the turbulent flow structure on particle deposition. In this paper, kinematic simulation (KS) has been adapted to be a sub‐grid model for particles, in conjunction with large eddy simulation (LES) in real space with boundaries. KS is a Lagrangian model of turbulent dispersion that takes into account the effects of spatio‐temporal flow structure on particle dispersion. It is a unified Lagrangian model of one‐, two‐ and indeed multi‐particle turbulent dispersion and can easily be used as a Lagrangian sub‐grid model for LES codes, thus enabling complex geometry to be taken into account. To study the effect of small‐scale flow structures on particle deposition in the ribbed channel flow, we use a validated LES code to simulate the flow field, and KS to model the sub‐grid flow structures. Thus, the large scales are resolved by the simulation and the small scales are modelled using various sub‐grid models. As none of the existing sub‐grid models is known to have taken into account the effects of small‐scale turbulent flow structures on particle deposition, it is important to use KS's ability to remodel the sub‐grid velocity field and thereby incorporate its effect on particle deposition. The parameters of our simulations for LES are the Reynolds number, width of the channel, height of the rib and sub‐gridmodel parameters. For KS, the parameters are the energy dissipation rate obtained from LES, the energy spectra, ratio of the largest and smallest sub‐grid scales and the total number of modes for the sub‐grid velocity field. The turbulent flow features thus obtained are compared with published experimental data in a ribbed channel. Our results suggest that while the small‐scale (sub‐grid) turbulent flow structures have negligible effects on particles with large relaxation times (compared with the Kolmogorov dissipation time scale), deposition of the particles with small relaxation times in the ribbed channel can be affected by these sub‐grids. Copyright © 2008 John Wiley & Sons, Ltd.