Entrainment and structure of negatively buoyant jets

Milton-McGurk, L.; Williamson, N.; Armfield, S.W.; Kirkpatrick, M.P.; Talluru, K. M.

doi:10.1017/jfm.2020.1068

Cited by 16 publications

(81 citation statements)

References 38 publications

(235 reference statements)

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“…By varying the ethanol and salt concentration of the source and ambient fluids, and adjusting the flow rate of the Ismatic MCP-Z gear pump used to drive the flow, source Froude and Reynolds numbers in the ranges 10 Fr o 30 and 2900 Re o 6000 were obtained. A list of the experiments performed in the present study, and those from Milton-McGurk et al (2021), is given in table 1. The source and ambient fluid are prepared the day before a given experiment to ensure that the temperature is constant, and sufficient time is given between individual runs (approximately 30 min) to ensure that there is no motion in the tank.…”

Section: Methodsmentioning

confidence: 99%

“…The experimental set-up and image processing procedures were first benchmarked for a turbulent neutral jet, with additional details given in Milton-McGurk et al (2020. In the following sections we will present data for fountains with 10 were obtained from the previous study, Milton-McGurk et al (2021), while the remaining NBJ and fountain data are from the present investigation.…”

Section: Methodsmentioning

confidence: 99%

“…Dimensionless scalar concentration (0 c 1) and buoyancy (mm s −2 ) are related by a constant such that b = c(ρ o − ρ a )g/ρ a . In Milton-McGurk et al (2021), these profiles were shown to be Gaussian over a range of axial locations (20 z/D 40), or equivalently, local Froude numbers, Fr (1.9 Fr 5.9), in the NBJ, which are given in figures 4(b) and 5(b). When normalised by the centreline quantities, wc and cc , and respective half-widths, r 1/2,w and r 1/2,c , these velocity and scalar profiles in the NBJ collapse onto a single curve.…”

Section: Flow Statistics In Fountains and Nbjsmentioning

confidence: 95%

“…In a study by the present authors, the initial NBJ stage of the flow was investigated experimentally using two-dimensional particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) (Milton-McGurk et al 2021;Talluru et al 2021). It was found that, like neutral jets and plumes, the velocity and buoyancy profiles take Gaussian shapes over a wide range of axial locations (20 z/D 40).…”

Section: Introductionmentioning

confidence: 98%

“…Another important difference between NBJs and neutral and positively buoyant jets/plumes is that the turbulence profiles, such as the Reynolds stress and axial fluctuations, do not scale with the mean flow. Entrainment in NBJs was also investigated in Milton-McGurk et al (2021), and was found to be similar to a neutral jet near the source where the flow is more momentum-dominated. Further along the NBJ, where the flow becomes more buoyancy-dominated, the direction of 'entrainment' is reversed and there is a net radial outflow of fluid from the NBJ to the ambient.…”

Section: Introductionmentioning

confidence: 99%

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Characterising entrainment in fountains and negatively buoyant jets

et al. 2022

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Turbulent fountain flow consists of two distinct stages, the initial ‘negatively buoyant jet’ (NBJ) stage, and the fully developed ‘fountain’ stage. The present study investigates both stages of the flow using particle image velocimetry and planar laser-induced fluorescence, over a range of source Froude numbers, $10\lesssim Fr_o\lesssim 30$ , and Reynolds numbers, $5500\lesssim Re_o\lesssim 7700$ . While the velocity and buoyancy profiles in NBJs take similar Gaussian shapes over a wide range of axial locations, this was not observed in fountains. The changing profile shape is most evident in the outer flow (OF) region, while there is a degree of similarity in the inner flow (IF). Entrainment between IF and OF is shown to depend on the local Richardson number, $Ri$ . The fountains are found to have a negative entrainment coefficient, $\alpha <0$ , for the majority of their height, implying a net radial outflow of fluid from the IF to the OF. An alternative description of entrainment is considered, the ‘decomposed top-hat’ model, where the radial flow is separated into inflow and outflow components that are then estimated using the present experimental data. The inflow component was found to be proportional to the axial IF velocity, which is similar to the classical description of entrainment in pure jets/plumes, while the outflow depends on the local $Ri$ . Entrainment in NBJs may also be described by this framework, which, despite not having an OF, is still subject to an $Ri$ -dependent radial outflow.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Flow Statistics In Fountains and Nbjsmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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