Abstract
Urban street canyon flows play a central role in microclimate control, from street canyon to neighbourhood and city scale, which affect pollutant dispersion, thermal comfort of residents and building energy consumption for various indoor and outdoor flow conditioning systems. Extensive studies have been devoted to this field, from theoretical modelling to experimental measurements and numerical simulations. While some important characteristics of street canyon flows, such as the presence of a primary standing vortex and the mechanism for its establishment, have been well revealed, a holistic understanding consolidating theoretical, experimental and numerical research has not been achieved. This review is therefore aimed to holistically articulate these approaches and research outcomes in the field. Some critical points overlooked in the literature are identified and commented on. These are: distinguishing gradient and bulk Richardson numbers; identifying dominant similarity characteristic numbers for scaling down models; predicting the condition in which thermal effects come into play; modelling the convective heat transfer in non-equilibrium mixed convection conditions using wall functions; and exploring the influence of neutral and non-neutral urban boundary layers on street canyon flows and associated passive scalar dispersion. The review is concluded with an outlook to most challenging research questions towards understanding of microclimate of full-scale realistic street canyons.
Highlights
Half of the global population are living in cities and the number is projected to increase to 70% in 2050 [1]
When it comes to solar-radiation induced thermal effects on flow dynamics and dispersion of pollutant within a street canyon, the above review has implied that laboratory studies, computational simulations and field measurements have led to different perspectives whether thermal effects are important
We have reviewed advances of studies on street canyon flows, from theoretical modelling to experimental studies and recent numerical simulations
Summary
Half of the global population are living in cities and the number is projected to increase to 70% in 2050 [1]. Among the complex physical mechanisms contributing to the urban heat island effect, street canyon flow is one of the most relevant in local thermal comfort [36,37,38], airborne pollutant dispersion [39,40,41,42,43] and ventilation around buildings [44,45,46,47,48] Studies of such flows started since the 1960s and have been one of the most important research topics in the context of urban microclimate. These studies encompass thermal conditions [27,37,38,39,44,50,51,52,53,54,55,56,57,58], geometrical vari ations [40,42,59,60,61,62,63,64,65] and characteristics of local wind [66,67,68]
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