The effect of placing a grid over the outlet of the three-dimensional turbulent wall jet

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.