Experiments and numerical simulations were conducted to investigate the dispersion of turbulent jets issuing from realistic pipe geometries. The effect of jet densities and Reynolds numbers on vertical buoyant jets were investigated, as they emerged from the side wall of a circular pipe, through a round orifice. Particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) techniques were employed simultaneously to provide time-averaged flow velocity and concentrations fields. Large eddy simulation (LES) was applied to provide further detail with regards to the three-dimensionality of air, helium, and hydrogen jets. These realistic jets were always asymmetric and found to deflect about the vertical axis. This deflection was influenced by buoyancy, where heavier gases deflected more than lighter gases. Significant turbulent mixing was also observed in the near field. The realistic jets, therefore, experienced faster velocity decay, and asymmetric jet spreading compared to round jets. These findings indicate that conventional round jet assumptions are, to some extent, inadequate to predict gas concentration, entrainment rates and, consequently, the extent of the flammability envelope of realistic gas leaks.

Buoyancy effects and nozzle geometry can have a significant impact on turbulent jet dispersion. This work was motivated by applications involving hydrogen. Using helium as an experimental proxy, buoyant horizontal jets issuing from a round orifice on the side wall of a circular tube were analysed experimentally using particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) techniques simultaneously to provide instantaneous and time-averaged flow fields of velocity and concentration. Effects of buoyancy and asymmetry on the resulting flow structure were studied over a range of Reynolds numbers and gas densities. Significant differences were found between the centreline trajectory, spreading rate, and velocity decay of conventional horizontal round axisymmetric jets issuing through flat plates and the pipeline leak-representative jets considered in the present study. The realistic pipeline jets were always asymmetric and found to deflect about the jet axis in the near field. In the far field, it was found that the realistic pipeline leak geometry causes buoyancy effects to dominate much sooner than expected compared to horizontal round jets issuing through flat plates. † Email address for correspondence: majids@uvic.ca arXiv:1811.05580v1 [physics.flu-dyn]

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The original work of Kang et al (2004 Meas. Sci. Technol. 15 1104–12) presents a scheme for correcting optical distortion caused by the curved surface of a droplet, and illustrates its application in PIV measurements of the velocity field inside evaporating liquid droplets. In this work we re-derive the correction algorithm and show that several terms in the original algorithm proposed by Kang et al are erroneous. This was not evident in the original work because the erroneous terms are negligible for droplets with approximately hemispherical shapes. However, for the more general situation of droplets that have shapes closer to that of a sphere, with heights much larger than their contact-line radii, these errors become quite significant. The corrected algorithm is presented and its application illustrated in comparison with that of Kang et al.

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