Large-Eddy Simulations of Stability-Varying Atmospheric Boundary Layer Flow over Isolated Buildings

Abstract

This study explores the response of flow around isolated cuboid buildings to variations in the incoming turbulence arising from changes in atmospheric boundary layer (ABL) stability using a building-resolving large-eddy simulation (LES) technique with explicit representation of building effects through an immersed body force method. An extensive suite of LES for a neutral ABL with different model resolution and advection scheme configurations reveals that at least 6, 12, and 24 grid points per building side are required in order to resolve building-induced vortex shedding, mean-flow features, and turbulence statistics, respectively, with an advection scheme of a minimum of third-order. Using model resolutions that meet this requirement, 21 building-resolving simulations are performed under varying atmospheric stability conditions, from weakly stable to convective ABLs, and for different building sizes (H), resulting in LABL/H ≈ 0.1 – 10, where LABL is the integral length scale of the incoming ABL turbulence. The building-induced flow features observed in the canonical neutral ABL simulation, e.g., the upstream horseshoe vortex and the downstream arch vortex, gradually weaken with increasing surface-driven convective instability due to the enhancement of background turbulent mixing. As a result, two local turbulence kinetic energy peaks on the lateral side of the building in non-convective cases are merged into a single peak in strong convective cases. By considering the ABL turbulence scale and building size altogether, it is shown that the building impact decreases with increasing LABL/H, as coherent turbulent structures in the ABL become more dominant over a building-induced flow response for LABL/H > 1.

Efficient Graphics Processing Unit Modeling of Street‐Scale Weather Effects in Support of Aerial Operations in the Urban Environment

“…The IBFM implemented within FastEddy has been validated using a dense network of field observations from the Joint Urban 2003 field experiment, demonstrating a predictive skill for urban flow, turbulence and dispersion on par with other LES models and in good agreement with observations (Muñoz-Esparza et al, 2020). In a recent study that employed the urban capabilities of FastEddy, the specific problem of grid resolution requirements for flow over buildings was addressed (Shin et al, 2021). As shown in Figure 2, 10-12 grid points per building side are required to capture the most relevant turbulence energy content, while vortex shedding features are captured with approximately six grid points (similar to the effective resolution of the advection scheme).…”

“…The stability of the ABL plays a critical role on the street-scale wind and TKE distributions. A recent study based on idealized LES experiments of flow over isolated buildings by Shin et al (2021) has shown that stable stratification effects lead to stronger flow modifications by the building, due to insufficient background mixing as compared to urban flows in the presence of convective ABLs. Beyond that, here we observe yet another interesting feature related to stability effects.…”