Qualitative and Quantitative Investigation of Multiple Large Eddy Simulation Aspects for Pollutant Dispersion in Street Canyons Using OpenFOAM

Abstract

Air pollution is probably the single largest environment risk to health and urban streets are the localized, relevant hotspots. Numerous studies reviewed the state-of-the-art models, proposed best-practice guidelines and explored, using various software, how different approaches (e.g., Reynolds-averaged Navier–Stokes (RANS), large eddy simulations (LES)) inter-compare. Open source tools are continuously attracting interest but lack of similar, extensive and comprehensive investigations. At the same time, their configuration varies significantly among the related studies leading to non-reproducible results. Therefore, the typical quasi-2D street canyon geometry was selected to employ the well-known open-source software OpenFOAM and to investigate and validate the main parameters affecting LES transient simulation of a pollutant dispersion. In brief, domain height slightly affected street level concentration but source height had a major impact. All sub-grid scale models predicted the velocity profiles adequately, but the k-equation SGS model best-resolved pollutant dispersion. Finally, an easily reproducible LES configuration is proposed that provided a satisfactory compromise between computational demands and accuracy.

Implicit Definition of Flow Patterns in Street Canyons—Recirculation Zone—Using Exploratory Quantitative and Qualitative Methods

“…On the other hand, it is problematic for the comparison with the three available experimental data sets. This was also pointed in our previous work [64] and occurs for x/W = 0.50, while the comparisons are excellent for x/W = 0.25 and 0.75 (not presented here). Nevertheless, all the tested SGS models and even the denser mesh (180 cells per height, instead of 120) did not solve the problem, but all the other validation metrics (i.e., LES_IQ v , FAC2, NMSE) were within the acceptable limits [64,69,70].…”

“…Finally, the standard deviation of the vertical velocity σ W /U ref is in good agreement with the numerical and experimental data in Figure 2d. From these comparisons and previous [64], the agreement between the current LES and the experimental and numerical data is judged as satisfactory. The comparison for the standard deviation of the horizontal velocity σU/Uref in Figure 2c is also excellent between U5AR100 and the experimental work from [66] for the whole range of z/H, while is good for the height of the building with the high resolution LES by Kikumoto and Ooka [68].…”

“…Finally, the standard deviation of the vertical velocity σW/Uref is in good agreement with the numerical and experimental data in Figure 2d. From these comparisons and previous [64], the agreement between the current LES and the experimental and numerical data is judged as satisfactory.…”

“…The workflow to arrive to this LES set-up was presented and discussed in our previous paper [64]. In this paper, comparisons are presented for the unity street canyon U5AR100 for the middle of the canyon with x/W = 0.…”

Effects of Ground Heating on Ventilation and Pollutant Transport in Three-Dimensional Urban Street Canyons with Unit Aspect Ratio

“…With the increasing use of CFD techniques, it is crucial to assess the performance of turbulence models adopted to estimate ventilation and pollutant dispersion in urban areas. Evaluations of turbulence models and physical parameters influencing CFD simulations have been conducted by Chatzimichailidis et al [13] for 2D street-canyon flows, by Tominaga and Stathopoulos [14] for three-dimensional (3D) street-canyon flows, by Dai et al [15] through flow and dispersion inside building arrays, and by Yoshie et al [16] through a simulation of flow and dispersion around a high-rise building under a weakly unstable condition. Chew et al [17] evaluated the performance of RANS and LES models in the simulations of reduced-scale and full-scale 2D street-canyon flows with windward wall heating.…”