Numerical modelling of flow and dispersion around Cinder Cone Butte

A finite-volume code (SWIFT) has been developed at the University of Surrey to compute flow and dispersion in stably-stratified flow over topography. An advanced pressure-correction algorithm is used to solve the incompressible flow equations on a terrain-following curvilinear grid. Turbulent transport is represented by a two-equation eddy-viscosity model using a length-scale-limiting strategy suitable for atmospheric boundary-layer applications. A detailed simulation is undertaken of one particular case-study hour in the Cinder Cone Butte dispersion experiment and concentrations compared with field and laboratory data. Flow-field calculations are consistent with strongly-stratified flow forced to move in horizontal planes around the base of the hill, although the calculated “dividing-streamline height” is an overestimate of the depth of this layer. Plumes from upwind sources exhibit a strong sensitivity to wind direction, in good agreement with towing-tank simulations. A number of assumptions widely used in regulatory dispersion models are found to be invalid.