MB2 Urban Environment 1

The predictive capabilities of a building-resolving prognostic numerical simulation model (urbanSTREAM) for small-scale (microscale) atmospheric flows in an urban environment will be evaluated based on detailed comparisons between the predictions and measurements of various flow quantities obtained in the Joint Urban 2003 (JU2003) field experiment in Oklahoma City. The prognostic model for the wind field in a cityscape is obtained by solving the unsteady Reynolds-averaged Navier-Stokes (URANS) and partially-resolved Navier-Stokes (PRNS) equations. For URANS, a two-equation k-s turbulence closure model is used. However, in contrast to conventional large-eddy simulation (LES), which is based on spatial filtering of the NS equation, PRNS solves the time-filtered NS equation. The latter approach provides a unified framework for the numerical simulation of turbulent flows, and includes URANS, LES and direct numerical simulation (DNS) as special cases, depending on how the cut-off frequency of the filter is chosen. A two-equation k-s PRNS is adopted here, with the eddy viscosity being multiplied by a resolution control parameter function which is dependent on the cut-off wave number (or, equivalently, the cut-off frequency) of the filter.