Reduced-scale numerical investigation of airflow around low-medium density neighbourhoods from the perspectives of drag force and ventilation efficiency

• Published in: Urban climate Vol. 58; p. 102158
• Main Authors: Zhang, Mingjie, Li, Jiaying, Palusci, Olga, Gao, Zhi, Ji, Guohua, Zhang, Jianshun, Buccolieri, Riccardo
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2024
• Subjects: Aerodynamic drag; City breathability; Drag area; Drag interpretation; Planar area density; Urban morphology; Aerodynamic drag; Drag area; City breathability; Drag interpretation; Planar area density; Urban morphology
• ISSN: 2212-0955; 2212-0955
• DOI: 10.1016/j.uclim.2024.102158

Relevant drag measurements in wind tunnels contributed to the drag parametrization. This reduced-scale numerical work further examines drag distribution and the relation between drag force and outdoor ventilation efficiency. Neighbourhood-like block arrays with planar area densities (λp) from 0.0625 to 0.25 and five distinct form types are investigated, extending a prior drag experiment solely on cube regular arrays. The approaching flow reshaped by these arrays exhibits flow adjustment and drag evolution. Drag distribution analysis demonstrates varied shelter effects and different shapes of sectional drag profiles. Arrays featuring larger λp and staggered layout generally exhibit higher normalized bulk drag force (Fbulk∗), but lower normalized frontal area-averaged drag (FAf,ave∗). Further, Fbulk∗ and FAf,ave∗ demonstrate strong negative correlations with normalized spatially averaged velocity, showing the potential to reflect the ventilation efficiency within neighbourhoods. Drag area density and drag-to-frontal area ratio are assessed as alternatives to interpret the drag, and it reveals half of the physical frontal area for medium arrays can serve as approximately estimated drag area. It is noted that the qualitative evaluation provides insights into the drag distribution and drag interpretation, while the quantitative correlation is limited to the examined morphological scenarios. •The shelter effect and sectional drag profile vary with neighbourhood forms.•Distinct negative regression models between FAf,ave∗, λp and H/W are presented.•Fbulk∗ and FAf,ave∗, strongly correlated with Uave/UH, can serve as wind indices.•Drag area density and drag-to-frontal area ratio are adopted for drag interpretation.