Measurements of flow velocity and scalar concentration in turbulent multi-component jets: asymmetry and buoyancy effects

Abstract

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]

Multi-component high aspect ratio turbulent jets issuing from non-planar nozzles

“…9a), the jets emerged from the slot with an initial semi top-hat profile, not shown here. This behaviour was also previously observed in the slot 1 measurements [2,3]. It should be noted that this semi top-hat profile was observed to deviate from the jet streamwise axis (xaxis) in the direction of flow inside the tube and was maintained up to x ∼ 5D eq Air (x-z plane), x=1D eq He (x-z plane), x=1D eq Air (x-z plane), x=3D eq He (x-z plane), x=3D eq Air (x-z plane), x=5D eq He (x-z plane), x=5D eq Air (x-z plane), x=20D eq He (x-z plane), x=20D eq Air (x-z plane), x=40D eq He (x-z plane), x=40D eq Air (x-z plane), Slot 1, x=30D eq He (x-z plane), Slot 1, x=30D eq Air (x-z plane), x=1D eq He (x-z plane), x=1D eq Air (x-z plane), x=3D eq He (x-z plane), x=3D eq Air (x-z plane), x=5D eq He (x-z plane), x=5D eq Air (x-z plane), x=20D eq He (x-z plane), x=20D eq Air (x-z plane), x=40D eq He (x-z plane), x=40D eq Air (x-z plane), Slot 1, x=30D eq He (x-z plane), Slot 1, x=30D eq X X Flow direction within the tube Air (x-z plane), x=1D eq He (x-z plane), x=1D eq Air (x-z plane), x=3D eq He (x-z plane), x=3D eq Air (x-z plane), x=5D eq He (x-z plane), x=5D eq Air (x-z plane), x=20D eq He (x-z plane), x=20D eq Air (x-z plane), x=40D eq He (x-z plane), x=40D eq Air (x-z plane), Slot 1, x=30D eq He (x-z plane), Slot 1, x=30D eq Air (x-z plane), x=1D eq He (x-z plane), x=1D eq Air (x-z plane), x=3D eq He (x-z plane), x=3D eq Air (x-z plane), x=5D eq He (x-z plane), x=5D eq Air (x-z plane), x=20D eq He (x-z plane), x=20D eq Air (x-z plane), x=40D eq He (x-z plane), x=40D eq Air (x-z plane), Slot 1, x=30D eq He (x-z plane), Slot 1, x=30D eq X X Flow direction within the tube distance from the slot.…”

“…It should be noted that the n-coordinate refers to lines which are normal to the centreline, aligned with the opposite direction of flow inside the tube, and coplanar with the x-z plane (see the coordinate system in Fig.1 e-f). The spreading rate in the opposite direction of the flow within the tube, near the potential-core region, was previously found to be higher in the 3D round jets (Slot 1) [2,3] compared to the slot 2 and slot 3 geometries of the current investigation.…”

“…Moreover, upon comparison of the helium slot 1 jets (AR = 1), the vertical orientation was found to have a faster mass fraction decay rate compared to the horizontal case. Such differences in behaviour was not observed for the air slot 1 jets, suggesting that buoyancy has a remarkable affect on the mass fraction decay rates [3]. On the other hand, for helium slot 2 experiments (AR = 10), a faster decay rate was observed for horizontal case compared to vertical orientation.…”

“…Air (x-y plane), x=1D eq He (x-y plane), x=1D eq Air (x-y plane), x=3D eq He (x-y plane), x=3D eq Air (x-y plane), x=5D eq He (x-y plane), x=5D eq Air (x-y plane), x=20D eq He (x-y plane), x=20D eq Air (x-y plane), x=40D eq He (x-y plane), x=40D eq Air (x-y plane), Slot 1, x=30D eq He (x-y plane), Slot 1, x=30D eq Air (x-y plane), x=1D eq He (x-y plane), x=1D eq Air (x-y plane), x=3D eq He (x-y plane), x=3D eq Air (x-y plane), x=5D eq He (x-y plane), x=5D eq Air (x-y plane), x=20D eq He (x-y plane), x=20D eq Air (x-y plane), x=40D eq He (x-y plane), x=40D eq X X Figure 8 were previously found to develop to the self-similar Gaussian distribution much closer to the orifice, beyond x > 5D eq [2,3]. Finally, the curves obtained for both gases were found to be in agreement with each other in the far field region.…”

“…The camera's field of view for all cases corresponded to a 38×28 mm 2 window with an approximate pixel size of 6.5 µm. The images were taken at a frequency of 5 Hz and then pro- of the experimental procedure can be found in [2,3].…”