Cesar Aguirre

Large-eddy simulation and Lagrangian stochastic modeling of passive scalar dispersion in a turbulent boundary layer

A large-eddy simulation (LES) with the dynamic Smagorinsky–Germano subgrid scale (SGS) model is used to study the passive scalar dispersion in a turbulent boundary layer. Instead of resolving the passive scalar transport equation, fluid particles containing scalar are tracked in a Lagrangian way. The Lagrangian velocity of each fluid particle is considered to have a large-scale part (directly computed by the LES) and a small-scale part. The movement of fluid elements containing scalar at a subgrid level is given by a three-dimensional Langevin model. The stochastic model is written in terms of SGS statistics at a mesh level. The results of the LES are compared with the wind-tunnel experiments of Fackrell and Robins (1982, Journal of Fluid Mechanics, 117, 1–26) and with the LES results of Sykes and Henn (1992, Atmospheric Environment A, 26, 3127–3144), who used a completely Eulerian approach with a non-dynamic SGS model. Our simulations predict the quantitative features of the experiments of Fackrell and Robins (1982, Journal Fluid Mechanics, 117, 1–26). Moreover, by using the Lagrangian approach, scalar fluxes are computed with no additional modeling assumptions and show good agreement with the experimental data. A classic mean-gradient model of the scalar flux is calculated from the computed results. The agreement between the directly computed fluxes and the classic mean-gradient model calculation is remarkable.

Computational Tools for the Simulation of Atmospheric Pollution Transport During a Severe Wind Event in Argentina

This chapter details the theoretical aspects of numerical methods for the simulation of atmospheric phenomena, such as severe thunderstorms and turbulent transport of the dangerous gases and solid particles into the atmospheric boundary layer. Numerical methods are included in computational algorithms to solve large turbulent scales using large eddy simulation (LES) techniques to obtain acceptable results of turbulent flows. However, microphysics processes involving evaporation, condensation and precipita‐ tion water using LES techniques are parameterized. These atmospheric processes are simulated using the advanced regional prediction systems (ARPS) code. On the contrary, atmospheric transport of pollutants is simulated using ARPS code coupled with a Lagrangian stochastic one-particle method. The theoretical details of this coupling are presented. Later, we show some laboratory experiments of plume dispersion emitted from gaseous sources, and the results of the computational simulation tool are compared after obtaining good agreement of the gas concentra‐ tions on the stream-wise vertical plane and over the ground. Finally, we present a simulation of a pollution event of copper solid particles at San Miguel de Tucumán city, Argentina. The geographical distributions of copper particle concentrations are in good agreement with the measurements carried out experimentally.