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Article

Turbulent structure of a simplified urban fluid flow studied through stereoscopic particle image velocimetry

Authors: Monnier, B., Goudarzi, S. A. , Vinuesa, R., Wark, C.
Document Type: Article
Pubstate: Published
Journal: Boundary-Layer Meteorol.
Volume: 166   239-268
Year: 2018

Abstract

Stereoscopic particle image velocimetry (SPIV) was used to provide a three-dimensional characterization of the flow around a simplified urban model defined by a 5 by 7 array of blocks, forming 4 parallel streets, perpendicular to the incoming wind direction corresponding to a 0 degree incidence angle. Channeling of the flow through the array under consideration was observed, and its effect increased as the incoming wind direction, or angle of incidence (AOI), was changed from 0 to 15, 30 and up to 45 degrees. The flow between blocks can be divided into two regions: a region of low turbulent kinetic energy (TKE) levels close to the leeward side of the upstream block, and a high-TKE area close to the downstream block. The center of the arch vortex is located in the low-TKE area, and two regions of large streamwise velocity fluctuation bound the vortex in the spanwise direction. Moreover, a region of large spanwise velocity fluctuation on the downstream block is found between the vortex legs. Our results indicate that the reorientation of the arch vortex at increasing AOIs is produced by the displacement of the different TKE regions and their interaction with the shear layers on the sides and on the top of the upstream and downstream blocks, respectively. There is also a close connection between the turbulent structure between the blocks and the wind gusts. The correlations among gust components were also studied, and it was found that in the near-wall region of the street the correlations between the streamwise and spanwise gusts Ruv were dominant for all four AOI cases. At higher wall-normal positions in the array, the Ruw correlation decreased with AOI, whereas the Ruv coefficient increased, and at AOI = 45 degrees all three correlations exhibited relatively high values of around 0.4.