Influence of atmospheric stability on air ventilation and thermal stress in a compact urban site by large eddy simulation

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Original languageEnglish
Article number109049
Journal / PublicationBuilding and Environment
Online published4 Apr 2022
Publication statusPublished - 15 May 2022


The assumption of neutral atmosphere in conventional evaluation of air ventilation and thermal stress in a compact urban area with weak wind environment may lead to errors. To assess this effect, this paper presents air ventilation and thermal stress assessment in a real subtropical urban area in Hong Kong by large eddy simulation considering stable, neutral, and unstable stratification. The air ventilation and thermal stress are measured by wind velocity ratio and Universal Thermal Climate Index, respectively. The atmospheric stabilities are quantified by vertical profiles of equivalent potential temperature based on daily radiosonde records in recent five years. The simulated results show that the conventional isothermal assumption underestimates the air ventilation capacity and overestimates the heat stress in the urban area in terms of reduced wind speeds and increased areas of strong heat stress at pedestrian-level height, respectively. The influence of urban morphology on air ventilation and thermal stress is investigated based on two urban geometry indices, namely ground coverage ratio and frontal area ratio. It is found that the ground coverage ratio is more relevant to the urban ventilation and thermal stress, but the correlations are weakened under unstable condition. On the other hand, the influence of the frontal area ratio is little. The findings of this study aim to provide a reference to the amendment of the current air ventilation assessment methodology which neglects the influence of atmospheric stability.

Research Area(s)

  • Air ventilation, Atmospheric stability, Large eddy simulation, Thermal stress, Urban area