Investigation of interunit dispersion in 2D street canyons: A scaled outdoor experiment

Abstract

A B S T R A C TInterunit dispersion problems have been studied previously mainly through on-site measurements, wind tunnel tests, and CFD simulations. In this study, a scaled outdoor experiment was conducted to examine the interunit dispersion characteristics in consecutive two-dimensional street canyons. Tracer gas (CO 2 ) was continuously released to simulate the pollutant dispersion routes between the rooms in street canyons. The wind velocity, wind direction, air temperature, and tracer gas concentrations were monitored simultaneously. Two important parameters, the air exchange rate and reentry ratio, were analyzed to reveal the ventilation performance and interunit dispersion of the rooms in the street canyons. Based on the real-time weather conditions, it was found that the ventilation performance of the source room varied according to the room location. The air exchange rate distribution of the leeward-side room was more stable than that of the windward side. The tracer gas was mainly transported in the vortex direction inside the street canyon, and the highest reentry ratio was observed at the room nearest to the source room along the transportation route. In addition, under real weather conditions, the rooms in the street canyon have a high probability of experiencing a high reentry ratio based on the maximum reentry ratio of each room. This study provides authentic airflow and pollutant dispersion information in the street canyons in an urban environment. The dataset of this experiment can be used to validate further numerical simulations.

Impact of Indoor-Outdoor Temperature Difference on Building Ventilation and Pollutant Dispersion within Urban Communities

“…Nevertheless, the cascading effect found in this work is an often-overlooked pathway of exposure. This effect was also found by many other previous research, both with numerical simulations [21,22] and scaled outdoor observations [29]. Furthermore, with cross ventilation, the flow from outdoor to indoor and the flow passing through the whole building could be another exposure pathway between different rooms or even different buildings, as concluded by [20].…”

“…The parameter air change per hour (ACH) is applied to evaluate the effect of the natural ventilation in the room [29]. Equations ( 3) and ( 4) are the definition of ACH.…”

“…Due to the development of research techniques, field observations [23][24][25], scaledmodel experiments [26][27][28][29], wind-tunnel experiments [30][31][32][33], and computational fluid dynamics (CFD) modelling [34][35][36][37][38][39][40][41] are widely used to study the flow and pollutants dispersion in idealized or real urban environments. Comparing to field observations and physical-model experiments [37,42,43], CFD modelling is an efficient tool with lower cost, higher temporal-spatial resolution, controllable boundary conditions and comprehensive investigations for multiple parameters [44][45][46].…”

Inverse identification of source location in a single-sided natural ventilation building

“…Ai et al [10] used CFD simulation to study inter-unit dispersion characteristics of indoor pollutants in multi-story single-sided natural ventilated buildings and analyzed the effects of wind direction and balconies. Recently, Dai et al [11] adopted outdoor scale experiment to explore the contaminant transmission route of natural ventilation buildings in the street canyon.…”

Ventilation in worker dormitories and its impact on the spread of respiratory droplets

“…Street canyons also play a significant role in interunit dispersion. A study found the CO2 tracer gas being main transported in the vortex direction formed by the freestream inside the canyon ( Dai, Mak, Zhang, Cui, & Hang, 2020 ).…”