Large-Eddy Simulation of Flows over Idealized Urban Roughness in Unstable Thermal Stratification
نویسندگان
چکیده
Large-eddy simulation (LES) equipped with the one-equation subgrid-scale (SGS) model is employed to investigate the mean flows and turbulence over idealized two-dimensional (2D) street canyons in various unstable thermal stratifications. The building-height-tostreet-width (aspect) ratio is equalto unity so the flows inside a street canyon are in the skimming flow regime. Periodic boundaries are assigned to the domain inlet and outlet, and the spanwise extent, simulating the infinite horizontally homogenous urban roughness. The buoyancy forceis modeled by Boussinesq approximation. In isothermal conditions, the flow exhibits a logarithmic mean velocity profile (law of the wall) in the region above theurban roughness elements. On the other hand, in thermal stratification with the presence of buoyancy force, the mean velocity profile deviates from its isothermal counterpart. The current LES results show that the deviation depends on the Richardson number, which is a measure of the relative contributions from natural convection and forced convection. In unstable stratification, the conventional law of the wall is modified by multiplying an empirical constant Ato the logarithmic term to account for the contributions from thermal stratification. It is found that, with increasing buoyancy force, the empirical constant A and the aerodynamic roughness length scale z0 decrease while the displacement height dincreases. We therefore hypothesize that the aerodynamic roughness length z0and the displacement height darefunctions of thermal stratification in addition to physical roughness geometry.
منابع مشابه
Mixed Large-Eddy Simulation Model for Turbulent Flows across Tube Bundles Using Parallel Coupled Multiblock NS Solver
In this study, turbulent flow around a tube bundle in non-orthogonal grid is simulated using the Large Eddy Simulation (LES) technique and parallelization of fully coupled Navier – Stokes (NS) equations. To model the small eddies, the Smagorinsky and a mixed model was used. This model represents the effect of dissipation and the grid-scale and subgrid-scale interactions. The fully coupled NS eq...
متن کاملMixed Large-Eddy Simulation Model for Turbulent Flows across Tube Bundles Using Parallel Coupled Multiblock NS Solver
In this study, turbulent flow around a tube bundle in non-orthogonal grid is simulated using the Large Eddy Simulation (LES) technique and parallelization of fully coupled Navier – Stokes (NS) equations. To model the small eddies, the Smagorinsky and a mixed model was used. This model represents the effect of dissipation and the grid-scale and subgrid-scale interactions. The fully coupled NS eq...
متن کاملLarge-eddy simulation of turbulent flow over an array of wall-mounted cubes submerged in an emulated atmospheric boundary-layer
Turbulent flow over an array of wall-mounted cubic obstacles has been numerically investigated using large-eddy simulation. The simulations have been performed using high-performance computations with local cluster systems. The array of cubes are fully submerged in a simulated deep rough-wall atmospheric boundary-layer with high turbulence intensity characteristics of environmental turbulent fl...
متن کاملSelf-Organization of Atmospheric Macroturbulence into Critical States of Weak Nonlinear Eddy–Eddy Interactions
It is generally held that atmospheric macroturbulence can be strongly nonlinear. Yet weakly nonlinear models successfully account for scales and structures of baroclinic eddies in Earth’s atmosphere. Here a theory and simulations with an idealized GCM are presented that suggest weakly nonlinear models are so successful because atmospheric macroturbulence organizes itself into critical states of...
متن کامل