Flow and dispersion over topography: A comparison between numerical and laboratory data for two-dimensional flows

Computations of the flow and dispersion over two-dimensional hills of various slope and submerged in a neutrally stable boundary layer are described. The results are compared with those of corresponding laboratory experiments undertaken by the U.S. Environmental Protection Agency (Khurshudyan et al., 1981, Report EPA-600/4-81-067). It is shown that a suitably modified k-v turbulence model generally produces reasonable agreement for the mean flow behaviour, but somewhat lower values for the turbulent kinetic energy and the lateral plume spread. This latter deficiency can be offset by normalising ground-level concentration values by the maximum value obtained in the absence of the hill. The resulting “terrain amplification factors” are in good agreement with the laboratory data. For a hill slope large enough to generate steady separation, the impact of the recirculating flow on concentration levels is also well predicted although, for somewhat lower slopes when separation is intermittent, results are less satisfactory.