Analysis of concentration fluctuations in gas dispersion around high-rise building for different incident wind directions

Abstract

This article presents experimental results that illustrate the unsteady characteristics of gas dispersion around a complex-shaped high-rise building for different incident wind directions. A series of wind tunnel experiments were conducted using a 1:30 scale model that represented the real structures under study. The objective of this paper is to study the behaviour of concentration fluctuations through transient analysis. Tracer gas was continuously released from a point source located at different positions, and a time series of fluctuating concentrations were recorded at a large number of points using fast flame ionization detectors. The experimental data were analysed to provide a comprehensive data set including variances and associated statistical quantities. Both the unsteady characteristics of the system and their potential practical impact are presented and discussed. Under crowd living conditions, the air pollutant exhausted from one household could probably re-enter into the neighbouring households, traveling with ambient airflow. Such pollutant dispersion process is defined as air cross-contamination in this study. The results indicate that the wind-induced cross-contamination around the studied type of high-rise building should not be overlooked, and the fluctuating concentrations should be paid attention to particularly during the evaluation of a potential contamination risk. This study can help deepen our understanding of the mechanisms of air cross-contamination, and will be useful for implementing optimization strategies to improve the built environments in metropolitan cities such as Hong Kong.

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

“…Similar dispersion characteristics can also be observed in other related studies ( Table 2) when more complicated HRR building models were investigated with a cross (#) floorplan shape [31][32][33][34]36,39] and an H-like floorplan shape [35], as shown in Fig. 7.…”

“…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.…”

“…Some risk assessment studies regarding the concerned airborne transmission have successfully used the Wells-Riley model to estimate the infection risk, by employing numerical simulations [29] and wind tunnel tests [33,34]. Although the combination of engineering and epidemiological studies is quite encouraging, the assessment need further investigation because many characteristics of indoor infectious droplets are still in question [43].…”

“…A series of wind tunnel experiments by Liu et al [31] and Wang et al [32] on scaled HRR models with a cross (#) floorplan have revealed that the wind-dominated inter-flat dispersion may occur along both horizontal and vertical directions. Then, Liu et al further designed detailed experiments to investigate such dispersion mechanism regarding mean concentrations with residents' behavior of window opening [33] and concentration fluctuations [34]. 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].…”

“…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.…”