Hot spots and flow structures around an isolated cuboid building subjected to surface warming: Large eddy simulations

Urban warming is evident in numerous cities. On especially hot days, building surfaces heat up, resulting in buoyancy-driven flows adjacent to these surfaces. As the intensity of these thermal effects escalates, the resulting airflow patterns exhibit increasing complexity, thereby facilitating the development of dynamic flow structures. The dynamics of flow structures are primarily influenced by the interaction between incoming wind and buoyancy-driven flows. This study used large eddy simulations to analyze airflow around an isolated cubic building with various heated surfaces, validated by wind tunnel tests. Under low wind speeds conditions, ranging from 0.5 to 2.0 m s⁻¹, the surface temperatures of the scaled building were kept between 20 and 95 °C. As the Richardson number (Ri) varied from 0 to 4.00, the flow, initially dominated by forced convection, gradually transitioned to mixed convection. At low wind speeds and high Ri values, thermal effects significantly altered the lengths of reattachment and recirculation regions, reducing them by up to 48.3% in certain cases. At pedestrian levels, thermally induced airflows often generated localized hot spots, especially around building corners and walls. This study emphasizes the pivotal role of buoyancy-driven flows in shaping building environments and how thermal effects influence airflow dynamics and the local microclimate. These findings offer key insights for developing climate change mitigation strategies and optimizing urban planning to improve sustainability.