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Natural ventilation assessment in typical open and semi-open urban environments under various wind directions

Hang, Jian, Luo, Zhiwen ORCID:, Sandberg, Mats and Gong, Jian 2013. Natural ventilation assessment in typical open and semi-open urban environments under various wind directions. Building and Environment 70 , pp. 318-333. 10.1016/j.buildenv.2013.09.002

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Semi-open street roofs protect pedestrians from intense sunshine and rains. Their effects on natural ventilation of urban canopy layers (UCL) are less understood. This paper investigates two idealized urban models consisting of 4(2 × 2) or 16(4 × 4) buildings under a neutral atmospheric condition with parallel (0°) or non-parallel (15°, 30°, 45°) approaching wind. The aspect ratio (building height (H)/street width (W)) is 1 and building width is B = 3H. Computational fluid dynamic (CFD) simulations were first validated by experimental data, confirming that standard k–ε model predicted airflow velocity better than RNG k–ε model, realizable k–ε model and Reynolds stress model. Three ventilation indices were numerically analyzed for ventilation assessment, including flow rates across street roofs and openings to show the mechanisms of air exchange, age of air to display how long external air reaches a place after entering UCL, and purging flow rate to quantify the net UCL ventilation capacity induced by mean flows and turbulence. Five semi-open roof types are studied: Walls being hung above street roofs (coverage ratio λa = 100%) at z = 1.5H, 1.2H, 1.1H (‘Hung1.5H’, ‘Hung1.2H’, ‘Hung1.1H’ types); Walls partly covering street roofs (λa = 80%) at z = H (‘Partly-covered’ type); Walls fully covering street roofs (λa = 100%) at z = H (‘Fully-covered’ type). They basically obtain worse UCL ventilation than open street roof type due to the decreased roof ventilation. ‘Hung1.1H’, ‘Hung1.2H’, ‘Hung1.5H’ types are better designs than ‘Fully-covered’ and ‘Partly-covered’ types. Greater urban size contains larger UCL volume and requires longer time to ventilate. The methodologies and ventilation indices are confirmed effective to quantify UCL ventilation.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Architecture
Publisher: Elsevier
ISSN: 0360-1323
Date of Acceptance: 5 September 2013
Last Modified: 10 Nov 2022 11:45

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