Numerical analysis of pollutant dispersion around elongated buildings: An embedded large eddy simulation approach

Abstract

High fidelity, scale-resolving numerical simulations of flow and pollutant dispersion around several elongated isolated buildings are presented in this paper. The embedded large eddy simulation (ELES) is used to model flow and concentration fields for six test cases with various source-building geometries. Specifically, the influence of building aspect ratio, wind direction, and source location is examined with these cases. Results obtained from the present ELES model are evaluated using available wind tunnel measurements, including those of streamwise and spanwise velocities, turbulent kinetic energy, and streamwise, lateral, and spanwise pollutant concentrations. Comparisons indicate that the ELES provides realistic representations of the flow and concentration fields observed in wind tunnel experiments, and captures several complex phenomena including the lateral shift and enhanced descent of the plume for rotated/elongated buildings. Furthermore, the ELES provides a means to study the advective and turbulent concentration fluxes, plume shapes, and geometry of vortical structures that is used to examine turbulent transport of pollutants around buildings. We investigate the enhancement of vertical and lateral plume spread as the building aspect ratio is increased. In addition, through the study of advective and turbulent concentration fluxes, we shed light on the physics behind higher ground-level concentrations observed for rotated buildings.

Enhancements to AERMOD's building downwash algorithms based on wind-tunnel and Embedded-LES modeling

“…Effectively, with a decrease in enhanced turbulence intensity, the rate of growth of σ z is lower in the eddy diffusivity region than it is in PDF region. This trend matches wind tunnel data from Perry et al (2016) and LES data from Foroutan et al (2018) that show enhanced turbulence intensity throughout the wake but higher values within the cavity, particularly at the outer cavity boundary (results not shown here).…”

“…The results of the numerical simulations compared favorably to the wind tunnel simulations (see Foroutan et al(2018) for a more complete description of the numerical simulations and their comparison to the wind tunnel results).…”

“…A recent extensive wind tunnel study (Perry et al, 2016) and associated large eddy simulation modeling (Foroutan et al, 2018) of building downwash around a range of rectangular buildings have provided the basis for a clearer understanding of the dominant features of pollutant dispersion in these complex and turbulent flow situations. This has allowed for a fresh examination of the performance of the AERMOD dispersion model and the development of improvements to AERMOD's building downwash algorithms.…”

“…Embedded Large Eddy Simulations (ELES) were performed for six of the cases from Perry et al (2016) to provide greater detail in the spatial and temporal variations in the velocity, turbulence, and concentrations fields (Foroutan et al, 2018). Denoting the cases with their aspect ratio, wind direction, stack height, and stack location, the six cases simulated were: 1: 1: 2 − 0° − 1.5H− 0, 1: 1: 2 − 45° − 1.5H − 0, 1: 1: 8 − 0° − 1.5H − 0, 1: 1: 8 − 45° − 1.5H −0, 1: 1: 2 − 0° − 1.5H − +, 1: 1: 2 − 0° − 1.2H − 0.…”

“…This paper is the third in a series reporting on an ongoing project to improve the performance of the building downwash algorithm. Two studies -a wind tunnel study (Perry et al, 2016) and complementary large eddy simulation (LES) study (Foroutan et al, 2018) -provide the basis for improvements to AERMOD. This paper reports on four specific changes: 1) improvement to the transition of plume material moving from the cavity into the far wake regions; 2) specification of an effective velocity that is more appropriate for diffusion estimates within the building wake; 3) modifications to the expressions for wake turbulence that more accurately reflect the original formulations of Weil (1996) upon which the wake model is based; and 4) a simple modification to the building preprocessor program for oblique wind angles.…”