Development of a building wake/stack height numerical modeling capability

We are developing state-of-the-art numerical tools which can be used to provide reliable estimates of potential emissions at various LLNL sites. In particular we have focused our efforts in generating models which can simulate the wind flow and dispersion of airborne pollutants around surface-mounted structures such as buildings or building complexes. To achieve this goal, we have adopted two different but complementary approaches in the modeling of this complex problem. The first approach employs a Reynolds-averaged set of equations whose solution results in a description of the mean flow and concentration pattern. In the second approach, we are developing a more advanced model based on the large eddy simulation (LES) concept. In this report, we describe the progress in the development of the two approaches. We begin by discussing the calculational procedure which has been chosen for the Reynolds-averaged model, namely: prediction of the mean flow via a turbulent flow model, and; employment of the calculated flow field to drive a particle-in-cell transport and diffusion model (ADPIC). The performance of this model is benchmarked against experimental data obtained for flow over a backward-facing step. The backward-facing step problem can be viewed as a simplification of a rectangular-shaped surface mounted obstacle. We next include a brief description of the LES method, the continuum and discretized LES equations, the numerical methodology, and some preliminary flow calculations. As with the Reynolds-averaged model, the backward- facing step is used to benchmark the LES model development. The results are in agreement with the calculations of other researchers. We conclude by discussing several improvements which will be considered as we continue the development of both the Reynolds-averaged and the LES models. 40 refs., 15 figs., 1 tab