Large eddy simulation of wind-induced interunit dispersion around multistory buildings

Abstract

Previous studies regarding interunit dispersion used Reynolds-averaged Navier-Stokes (RANS) models and thus obtained only mean dispersion routes and re-entry ratios. Given that the envelope flow around a building is highly fluctuating, mean values could be insufficient to describe interunit dispersion. This study investigates the wind-induced interunit dispersion around multistory buildings using the large eddy simulation (LES) method. This is the first time interunit dispersion has been investigated transiently using a LES model. The quality of the selected LES model is seriously assured through both experimental validation and sensitivity analyses. Two aspects are paid special attention: (i) comparison of dispersion routes with those provided by previous RANS simulations and (ii) comparison of timescales with those of natural ventilation and the survival times of pathogens. The LES results reveal larger dispersion scopes than the RANS results. Such larger scopes could be caused by the fluctuating and stochastic nature of envelope flows, which, however, is canceled out by the inherent Reynolds-averaged treatment of RANS models. The timescales of interunit dispersion are comparable with those of natural ventilation. They are much shorter than the survival time of most pathogens under ordinary physical environments, indicating that interunit dispersion is a valid route for disease transmission.

The airborne transmission of infection between flats in high-rise residential buildings: A review

“…However, existing studies have not provided a general secure threshold for the re-entry ratio to quantitatively evaluate the infectious risk for a specific flat by this kind of cross-contamination. This is due to the diverse pathogen types and different physical conditions of susceptible people [40]. Although previous researchers [42,86] have studied the possibility of causing disease by pathogens, the results are shown to be strongly case-dependent.…”

“…Passive tracer gases, such as carbon dioxide (CO 2 ), sulfur hexafluoride (SF 6 ), propane (C 3 H 8 ) and haze-fog (HF), have been successfully and widely used in experimental and numerical studies of the inter-flat transmission and dispersion [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. The reason lies in the similarity of their aerodynamic behaviors to those various gaseous pollutants and fine aerosols.…”

“…Considering the uncontrollable atmospheric conditions during on-site measurements and the scale problems of wind tunnel tests [70,71], Ai et al performed numerical simulations to study the wind-dominated inter-flat dispersion in a multi-storey slab-like building in terms of mean process using the optimized RNG model with the two-layer near-wall model [37,38], and transient process using LES model [40]. Besides, Ai et al [37,38,40] further investigated the effects of balcony on the dispersion behavior, which is out of the scope of this paper.…”

“…7(a). Moreover, simulation results by Ai and Mak [40] using LES on a slab-like building pointed out that: 1) the incursion of pollutants into a specific flat is intermittent, 2) secondary dispersions are observed, and 3) a flat with a very low mean re-entry ratio could occasionally experience extremely high re-entry ratios. These findings further extend the dispersion scope and highlight the dispersion uncertainty for inter-flat cross-contamination, which were unfortunately ruled out by the inherent time-averaged treatment of previous RANS models [27][28][29][30]37,38].…”

“…Previous on-site measurements [25,26] and numerical simulations [27][28][29][30] on buoyancy-dominated inter-flat transmission well explained and quantified the upward vertical transport of gaseous pollutants. Later, a series of wind tunnel tests [31][32][33][34] and numerical simulations [35][36][37][38][39][40] was carefully performed to study the inter-flat airborne transmission and dispersion dominated by wind effect. In addition, a few studies [26,29,39] provided some preliminary work on the dispersion mechanism driven by combined buoyancy and wind effect.…”