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USE OF PROPER ORTHOGONAL DECOMPOSITION TO INVESTIGATE THE TURBULENT WAKE OF A SURFACE-MOUNTED FINITE SQUARE PRISM

Rajat Chakravarty
Department of Mechanical Engineering, University of Saskatchewan, Saskatoon, SK, S7N 5A9, Canada

Nader Moazamigoodarzi
Department of Mechanical Engineering University of Saskatchewan 57 Campus Drive, Saskatoon, Saskatchewan, S7N 5A2, Canada

Donald J. Bergstrom
Department of Mechanical Engineering, University of Saskatchewan, Saskatoon, SK, S7N 5A9, Canada

David Sumner
Department of Mechanical Engineering University of Saskatchewan 57 Campus Drive, Saskatoon, Saskatchewan, S7N 5A2, Canada

Abstract

This study aims to investigate the characteristics of the instantaneous velocity field in select vertical planes located in the turbulent wake of a surface-mounted finite square prism. The instantaneous velocity field is obtained from a Large Eddy Simulation (LES); state-of-the-art post-processing methodologies namely the Proper Orthogonal Decomposition (POD) and the swirling strength criterion are used to analyse the flow structure. The study specifically considers the flow over a square prism of aspect ratio AR = 3 (AR = H/D where H is the height and D is the prism width) mounted on a ground plane and located within a thin laminar boundary layer. The Reynolds number based on the freestream velocity and cylinder width is Re = 500, and the angle of incidence is zero. POD is used to extract the dominant flow features, especially those related to vortex shedding, while the swirling strength criterion is used to visualise the smallscale turbulent structures. A principal conclusion of the study is that strong periodicity is observed in a transverse plane located 3.5D downstream of the prism, whereas the vertical mid-plane revealed a more complicated periodic structure. No compelling evidence of half-loop structures was obtained based on the analysis of the flow for a single periodic cycle. On the other hand, strong streamwise vortex structures were observed in the transverse plane in the upper region of the wake, somewhat reminiscent of but not the same as tip vortices.