Research on the vortical and turbulent structures in the lobed jet flow using laser induced fluorescence and particle image velocimetry techniques

Abstract

The changes in vortical and turbulent structure in the near field (X/D < 3.0) of jet mixing flow caused by a lobed nozzle were investigated experimentally in the present study. The techniques of planar laser induced fluorescence and particle image velocimetry were used to accomplish flow visualization and velocity field measurements. The experimental results showed that, compared with a circular jet flow, lobed jet mixing flow was found to have a shorter laminar region, a smaller scale of the spanwise Kelvin-Helmholtz vortices, earlier appearance of small scale turbulent structures and a larger region of intensive mixing in the near field of the jet mixing flow. The central line velocity decay of the lobed jet mixing flow was also found to be much faster than that in a conventional circular jet. All these indicated that the lobed nozzle provides better mixing performance than does a conventional circular nozzle.

Impinging cross-shaped submerged jet on a flat plate: a comparison of plane and hemispherical orifice nozzles

“…The mean streamwise profile of the convergent nozzle is flat (Fig.4 a) while for the Cross-Shaped nozzles, a two-step distribution characterized the major plane (Fig.4 a). The same behaviour was also observed by Nastase et al [52] in a free jet from a cross-shaped orifice and by Hu et al [53] in a six-lobed nozzle jet. This is because in the lobed jets, the major plane has two shear layers: the inner shear layer between the jet central core and the lobes, and the outer shear layer between the jet flow and its ambience.…”

“…A wide region of intensive mixing characterized by high turbulence intensity (around 30% of W0) could be observed with jets from the CO/P and CO/H nozzles. Nearly identical turbulence profiles were measured by Hu et al [53] in their six-lobed jet.…”

Jet impingement heat transfer from lobed nozzles

“…This behaviour was also reported by previous researchers in 3D lobed geometries. Hu et al [43] reported that the potential core region at the centre of their three-dimensional six-lobe jet flow was much smaller and shorter than that in the circular jet flow. However, as Nastase and Meslem [41] mentioned, it should be underlined that the performance of the lobed jet is not limited to its potential core region.…”

On the Lagrangian features of circular and semicircular jets via 3D Particle Tracking Velocimetry

“…Point measurements with hotwire anemometry have been extensively used to study, for example, the effect of nozzle shape on the mixing along the jet axis [8], characteristics of jet impingement cooling [9], the influence long slot nozzle geometry on a plane jet [10], and turbulence characteristics of jets from a triangular orifice [11]. Particle image velocimetry (PIV) has been used to investigate synthetic jets issuing from different non-circular nozzle shape at high Reynolds numbers [2], subcooled boiling in bubble-top jet flows [12,13], and lobed jets [14], among others. Tomographic PIV has also been used in planar jet flows to characterize 3D vortex structures [15].…”