Abstract
Large-Eddy Simulation (LES) numerical experiments of neutrally-stratified turbulent flow over an urban-type surface and passive scalar transport by this flow are performed. A simple parameterization of the turbulent length scale containing only one empirical constant is proposed. Multilayer Reynolds-Averaged Navier-Stokes (RANS) model of turbulent flow and turbulent scalar diffusion is constructed. The results of the RANS model are compared with the LES experiments. It is shown that the proposed approach allows predicting the average flow velocity and the scalar concentration inside and above the urban canopy.
Highlights
Increasing performance of supercomputers makes it possible to make detailed weather forecasts, in which the horizontal scale of large metropolitan areas is resolved explicitly on grids of General Circulation Models (GCMs)
The plots are arranged by columns, each representing different geometry configurations of urban canopy
The Large-Eddy Simulation (LES) was used as a benchmark for evaluation of multilayer local one-dimensional Reynolds-Averaged Navier-Stokes (RANS) models of urban canopy
Summary
Increasing performance of supercomputers makes it possible to make detailed weather forecasts, in which the horizontal scale of large metropolitan areas is resolved explicitly on grids of General Circulation Models (GCMs). It is necessary to develop multilayer one-dimensional turbulence models that take into account the dynamic and thermal effects of buildings and vegetation on turbulence in the form of vertically distributed forcing and incorporate special turbulent closures for them In such models, the surface layer is considered as a porous medium, which creates volumetric resistance to the mean wind and is capable of generating turbulent kinetic energy in the flow around buildings. Researchers resort to some combined way of organizing measurements, placing large arrays of simple in shape large objects (e.g., cubes of a 1.5 m size) in the open air, rather than in the laboratory setup (see, experiment COSMO (Comprehensive Outdoor Scale Model) http://www.ide.titech.ac.jp/ kandalab/COSMO/COSMO.html [13]) This approach provided reliable data for developing parameterizations of the dynamic and thermal interaction of turbulence with urban-type surfaces (see, e.g., [12]).
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