Urban ventilation assessment with improved vertical wind profile in high-density cities-Investigations in nighttime extreme heat

He, Yueyang, Yuan, Chao, Ren, Chao, Wang, Weiwen, Shi, Yuan ORCID: 0000-0003-4011-8735 and Ng, Edward
(2022) Urban ventilation assessment with improved vertical wind profile in high-density cities-Investigations in nighttime extreme heat. BUILDING AND ENVIRONMENT, 216. p. 109018.

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Climate change and heatwaves challenge urban dwellers’ thermal comfort and health. In Hong Kong, more frequent and intensive extreme heat has been observed recently. This study uses Light Detection and Ranging (LiDAR) to observe vertical wind profiles and calibrate numerical simulation methods for urban ventilation assessment in nighttime extreme heat (i.e. hot nights (HNs)) at a high-density site. A cross-comparison is conducted to the characteristics between the observed HN-averaged wind profiles and commonly-used 24-h-period-averaged wind profiles in summer. The observation reveals a weaker wind environment in HNs than 24-h-periods, and the weakest condition is found in HNs during prolonged extreme heat where the impacts of weakened advection surpass enhanced thermal buoyancy. Furthermore, CFD simulations are conducted to evaluate the deviations on urban ventilation assessment caused by the lack of consideration of nighttime extreme heat when setting inlet wind profiles and site thermal conditions. In the simulation results, the 24-h-period-averaged wind profiles cause significant deviations on pedestrian-level wind speed and velocity ratio (empirical model (>45%); LiDAR observation (>20%)). Considerable deviations are found when unstable thermal stratification is ignored (>20%). Consistent deviations on vertical turbulent flow structures induced by the inexplicit coupling between thermal buoyancy and advection are found. The findings call for urgent attention to the wind conditions in HNs since they are most needed for releasing heat stress and urban overheating. It is recommended to include explicit buoyancy effects in both measurement and modeling works to optimize urban ventilation assessment for tackling extremely high-temperature and weak-wind conditions.

Item Type: Article
Uncontrolled Keywords: Heatwave, Vertical wind speed profile, Urban ventilation, High-density city, Doppler LiDAR, CFD
Divisions: Faculty of Science and Engineering > School of Environmental Sciences
Depositing User: Symplectic Admin
Date Deposited: 26 Jul 2022 09:21
Last Modified: 25 Mar 2023 02:30
DOI: 10.1016/j.buildenv.2022.109018
Related URLs:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3159234