Modelling considerations for examining the mean and unsteady flow in a simple urban-type street canyon

摘要

Different approaches to wind tunnel modelling of the flow in a single urban street canyon are discussed, with the emphasis on achieving approach flow conditions that most closely represent the full-scale case whilst maintaining a simple geometry for studying the mean and turbulent dynamics that ventilate pollutants from the street. Wind tunnel measurements using particle image velocimetry within a square section canyon of lateral length/height from 1 to 20, immersed in an array of cubic roughness elements of the same height, are compared with those from studies with different upstream roughness. It is shown that the canyon mean flow is dependant upon the nature of the flow separation from the roof of the upstream canyon building which, in turn, is related to the approaching flow conditions. Unless care is taken when modelling these conditions it is unlikely that the resulting canyon shear layer dynamics will be represented correctly.