| Deteriorating ambient air quality causes increasing concern to control authorities, human inhabitants and environmentalists. Air pollution, mostly from traffic emissions, is difficult to disperse and may accumulate within narrow street canyons among tall buildings, resulting in high pollutant concentrations. Reducing health risks from the accidental or deliberate release of Chemical, Biological, or Radioactive (CBR) agents and pollutants from industrial leaks, spills, and fire motivates this work. For these reasons it has become important to predict the flow field in urban topography. As a part of this work a large eddy simulation (LES) model has been developed. The model has been validated for various laminar and turbulent test cases.;Understanding the relationship between turbulent flow characteristics and surface geometry is very important for extenuating urban atmospheric problems such as air pollution, the heat island effect and other transport urban phenomenon. High resolution, LES of neutral flow through an array of cubes has been conducted with periodic boundary conditions in lateral and longitudinal directions. The LES model is then used to investigate the physical mechanisms that lead to the low turbulent stresses that have been reported in the lower half of the urban canopy layer.;A fast-running pressure solver has been developed that works within the Quick Urban & Industrial Complex (QUIC) Dispersion Modeling System. A pressure solver is necessary because the QUIC wind model is diagnostic and thus does not solve the full momentum equation nor produce pressure fields. The pressure solver utilizes the 3D mean wind fields produced by the QUIC wind model and rapidly computes a corresponding pressure field around and on the faces of the buildings.;Several fast-response dispersion models have been developed to account for the effects of a single building or group of buildings. In general, these models do not explicitly compute the velocity field around the buildings but are parametrically derived. Due to these issues, there is need to go back to computational fluid dynamics (CFD) to develop a fast CFD based model for urban areas that can give reasonably accurate results (velocity, turbulence and pressure fields) in minutes and has a fair balance between runtime and accuracy. As a part of the QUIC, a fast CFD based model has been developed: QUIC-CFD, which satisfies the above needs. |
