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A POD INVESTIGATION OF THE THREE-DIMENSIONAL WALL JET NEAR FIELD

Lhendup Namgyal
Department of Mechanical Engineering University of New Brunswick Fredericton, New Brunswick, Canada

Joseph W. Hall
Department of Mechanical Engineering University of New Brunswick Fredericton, New Brunswick, Canada

Abstract

A turbulent three-dimensional wall jet was investigated at an exit Reynolds number of 2.5×105 using Stereoscopic Particle Image Velocimetry (PIV) in the near-field region (x/D=5). The Proper Orthogonal Decomposition (POD) was applied to all three components of the velocity field to investigate the underlying coherent structures in the flow Low-dimensional reconstructions of the turbulent velocity field using the first 5 POD modes showed that the streamwise flow contours are significantly distorted from the mean. This was induced by coherent streamwise vortex structures formed in the outer shear-layers of the wall jet, not unlike those found in free jets. The reconstructed instantaneous streamwise vorticity indicates the presence of a persistent vortex pair close to the wall and on either side of the jet centreline that are similar to the mean streamwise vorticity. These regions do not appear to be directly related to the streamwise vortex structures in the outer shear-layers.