Abstract
This study investigates airflow and turbulence within varying roof configurations in urban boundary layers by using the parallelized large-eddy simulation model (PALM). Key findings reveal stark contrasts in airflow between stepped and flat roof arrangements, with the former presenting dual counter-rotating vortices and enhanced vertical motion in one street, while the latter exhibited a primary vortex and several secondary vortices. Additionally, normalized turbulence kinetic energy (TKE) was markedly lower in flat roof configurations, with stepped roofs fostering more significant turbulence and small-scale turbulent motion. This variability intensified with decreasing step height and quantity. Vertical profiles further disclosed considerable velocity disturbances and larger Reynolds numbers in one street of stepped roofs, affirming the roof’s influence on turbulence generation and transport. Dispersive stress also displayed differing characteristics in various canyons. Turbulent momentum transport through eddies significantly differs between the windward and leeward streets of flat and stepped roofs. Further exploration into density stratification effects and scalar transport in stepped roofs would enhance practical implications.
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