The effect of placing a grid over the outlet of the three-dimensional turbulent wall jet
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Date
2013
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University of New Brunswick
Abstract
The three-dimensional turbulent wall jet has a lateral half-width that is 5 to 8 times
greater than its vertical half-height. This has been previously attributed to strong
turbulence generated secondary flow caused by the passage of coherent vortex-ring
structures formed at the nozzle exit. In order to assess whether the large lateral growth
of the jet is tied to these structures, a grid was placed at the nozzle exit to disrupt the
shear-layer that produces the vortex rings at the outlet. Here, the jet was formed using a
0.038m round contoured nozzle with an exit Reynolds number of 108,000. The grid has
a mesh wire size of 0.2mm with an opening of 1mm giving it a solidity ratio of 0.4.
Measurements of the jet with and without the grid were taken using hot-wire
anemometry and stereoscopic Particle Image Velocimetry (PIV). The results indicate
that the grid delays the lateral growth of the jet and increases its vertical growth. By
x/0=40 though, these differences were minimal. The presence of the grid also decreased
the mass entrainment and mixing associated with the jet at each downstream location
investigated.