A three-equation model of the turbulent transport of momentum and heat for simulating a circulation structure and dispersion pollutant over the urban heat island in a stably stratified environment under nearly calm conditions is formulated. Turbulent fluxes of momentum - and heat - determined from E-ε-<θ~2> turbulence model. This model minimizes difficulties in simulating the turbulent transport in a stably stratified environment and reduces efforts needed for the numerical implementation of the model. The numerical results demonstrate that the three-equation model is able to predict the structure of turbulent circulation flow induced by the heat island that is in good agreement with the experimental data. The Eulerian models of a dispersion of air pollution are formulated: a high-order closure dispersion model in which the concentration fluxes are calculated from the transport equations (DC-model), and an algebraic model of turbulent fluxes (AC-model) obtained by simplification of DC-model to the algebraic expressions in the weakequilibrium approximation. Both models use mean wind and turbulence quantities from a second-order closure model of the atmospheric boundary layer (the three-parametrical E-ε-<θ~2> turbulence model). Results from dispersion of a passive contaminant from the surface source obtained with help DC and AC models show that the maximum difference of concentration level near to a source does not exceed ten percents. Besides it is shown, that diffusion terms of DC-models excluded at obtaining of AC-model, act to smooth out the gradients of the turbulent fluxes. The concentration field calculated with the DC-model turns out more smooth, than calculated by AC-model. The executed verification specifies validity of use of algebraic AC-model in practice of modeling and simulation of turbulent stratified flows and atmospheric contaminant dispersion, in particular.
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