Dispersion around an L-Shape building: comparisons between wind tunnel data and the RUSTIC/MESO models

ITT Industries, Advanced Engineering and Sciences has developed two models to predict air flow and dispersion in urban environments. The first model (RUSTIC) is a fast running urban air flow code that rapidly converges to a numerical solution to a modified set of the compressible Navier-Stokes equations. The model also includes a k-ù turbulence model and atmospheric stability. The second model (MESO) is a mesoscale Lagrangian particle transport and diffusion code that can predict concentrations of a released chemical or biological agent.

As a preliminary validation of the models, concentrations predicted by MESO are compared to experimental data from a wind tunnel test (Cowan, Castro and Robbins 1995). A brief overview of the wind tunnel test is as follows. First, a 1:200 full scale model of an L-shaped building is placed in a wind tunnel and the building is oriented at both 0° and 45° to the impinging wind. Then a neutrally buoyant tracer gas is emitted from a door in the building, and concentrations of this gas are measured at a lateral cross section downwind from the building.

RUSTIC/MESO is setup with the initial conditions of the wind tunnel experiment, and the steady-state concentrations predicted by the models are compared to the wind tunnel data at this lateral cross section. At most heights, a favorable comparison is seen for both concentration magnitudes and lateral distribution of the gas; validating the models in this idealized scenario.