Three-Dimensional Numerical Simulation of Plume Downwash with a k–ϵ Turbulence Model

Abstract

Plume downwash at a large oil-gathering facility in the Prudhoe Bay, Alaska oil-field reservation was simulated in a series of numerical experiments. The purpose of this study was to investigate the potential of the numerical model as a means of assessing the impact of pollutants emitted from buoyant sources influenced by complex aerodynamic wakes. The model is a three-dimensional, Cartesian coordinate, finite difference code that solves the nonhydrostatic, time-averaged equations for the conservation of momentum and energy. The code uses a modified form of the standard first-order, two-equation (k??) engineering turbulence closure model. Wind tunnel and field investigations of dispersion at this arctic industrial complex indicate that dispersion is significantly influenced by building-generated airflow disturbances. We have used the numerical model to simulate directly the mean features of the flow field and dispersion from a buoyant source at an industrial site. The flow features varied depending on the size, number, and orientation of the buildings. A recirculation cavity was present in all model simulations and varied from 0.8 HB to 2 HB (building height). This agrees closely with results of wind tunnel studies. The model simulates a velocity defect of 0.6, a factor of 3.4 increase (relative to the approach flow) in turbulent kinetic energy (k), a factor of 5 increase in dissipation of k(?), and a 45% increase in turbulent viscosity at a downwind distance of 2 HB from the building. At a downwind distance of 5 HB, the plume rise of the simulated thermal plume decreased by 70% compared to the no-building case while the vertical and horizontal widths of the plume increased by 45% and 30%, respectively. These results generally reproduce the plume downwash and dispersion observed in wind tunnel and field investigations.