Heat and flow dynamics in cities: an experimental comparative study across diverse urban morphologies.

Urban areas are renowned for their intricate atmospheric dynamics, influenced by diverse building configurations. Understanding the implications of urban morphology for flow patterns, ventilation and heat dissipation is crucial for urban climate management. However, comprehending the interplay between thermal-driven buoyancy flow and urban morphology remains a challenge. To address this gap, we measured heat transport and fluid flow around three-dimensional parametric urban models resembling Singapore's urban morphology accounting for buoyancy effects, using simultaneous Particle Image Velocimetry (PIV) and Laser-Induced Fluorescence (LIF) measurements. Our study meticulously documents the development of non-isothermal urban flow, highlighting heat plume generation from the ground, buoyant updraft development and temperature variations along the flow. The variations in urban morphologies have a profound impact on these developmental processes, resulting in substantial differences in heat and flow mechanisms, ventilation efficiency and heat removal performance. For example, significant differences are observed in ventilation rates and their fluctuations, with values reaching up to approximately 10.5 times and 12.2 times, respectively. These findings of the fluid flow and heat spreading above the ground contribute to the broader understanding of urban heat dynamics by demonstrating how localized thermal effects propagate through urban environments, influencing microclimatic conditions.This article is part of the theme issue 'Urban heat spreading above and below ground'.