DOI: 10.1615/TSFP7
DYNAMICS OF THE LARGE-SCALE STRUCTURES OVER A STREET CANYON IN AN URBAN-TYPE BOUNDARY LAYER
SINOPSIS
Wind tunnel PIV experiments were performed in order to investigate the dynamics of the large-scale structures over a street canyon model which consists of two parallel obstacles placed perpendicular to the main flow. The oncoming flow was an urban-type boundary layer developing over roughness elements the height of which was more than ten percent of the boundary layer depth. Attention was concentrated on the dynamics of the shear layer emanating from the top of the upstream obstacle and the occurrence of unsteady penetration and ejection of fluid from the canyon. The investigation of the structure of the shear layer region was performed via the analysis of two-point spatial correlations and the use of Proper Orthogonal Decomposition and conditional averaging techniques. It was found that the shear layer separating from the upstream obstacle was animated by a coherent flapping motion and generated large-scale vortical structures. These structures were alternatively injected into the canyon or shed off the obstacle downstream in the outer flow. Unsteady fluid exchanges between the canyon cavity and the outer flow were found to be mainly driven by the shear layer separating from the upstream obstacle.