Turbulence structure of neutral and negatively buoyant jets

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

doi:10.1017/jfm.2020.921

Cited by 15 publications

(8 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, in a turbulent fountain, where the buoyancy opposes the momentum, there is the dampening of turbulence in the flow as observed in our previous study (Talluru et al. 2021). For instance, in the seven experimental cases presented in this study, is highest for ; however, the turbulence intensity is maximum for , where the dampening effect of buoyancy is relatively reduced compared with .…”

Section: Discussionsupporting

confidence: 66%

“…(2020) and the results have been validated in Talluru et al. (2021) and Milton-McGurk et al. (2021).…”

Section: Methodsmentioning

confidence: 59%

“…A combination of particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) measurement techniques was used to obtain simultaneous velocity and concentration measurements in the symmetric plane of the fountain top. Full details of the experimental procedures are given in Milton-McGurk et al (2020) and the results have been validated in Talluru et al (2021) andMilton-McGurk et al (2021). Hence, the details are briefly discussed here.…”

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Entrainment and dilution in a fountain top

2022

Self Cite

View full text Add to dashboard Cite

Experiments are carried out on a turbulent fountain to investigate the entrainment of ambient fluid and the dilution of scalar concentration in the fountain top (also referred to as the ‘cap’). The source Froude number ( $Fr_o$ ), defined based on the density difference between the source and the ambient fluids, is varied between 10 and 30, while the Reynolds number ( $Re_o$ ) is set to a minimum of 3000 to ensure a fully turbulent flow at the source. High-fidelity velocity and concentration measurements are obtained using particle image velocimetry and planar laser induced fluorescence techniques, respectively. The mean concentration field indicates that the cap is approximately hemispherical and its base is characterised by the local Froude number $Fr_z \approx 1.5$ . It is observed that the ratio of the entrained ( $Q_{top}$ ) volume flux in the fountain top and the volume flux supplied ( $Q_{in}$ ) at the base of the cap varies between 1.5 and 3.5 at different $Fr_o$ , exceeding the values of $Q_{top}/Q_{in} (= 0.5\text {--}0.8)$ for a fountain developing across a density interface (Lin & Linden, J. Fluid Mech., vol. 542, 2005, pp. 25–52). The present experimental results for $Q_{top}/Q_{in}$ are in excellent agreement with published numerical simulations of turbulent fountains at similar $Fr_o$ . Lastly, a robust metric to estimate the dilution of scalar in the fountain top has been proposed. The results clearly indicate that dilution is not equal to the entrainment ratio; however, the self-similarity of non-dimensional dilution profiles at different $Fr_o$ suggests that the phenomenological model for entrainment in the fountain top put forth by Debugne & Hunt (J. Fluid Mech., vol. 796, 2016, pp. 195–210), can also be effectively used to model the dilution of scalar concentration in the cap. Further, it is found that the variation of the dilution ratio is closely linked to the local Reynolds number ( $Re_z$ ) at the base of the cap. This is verified using an analytical model that describes the dependency of $Re_z$ on the local and source parameters – $Fr_z$ , $Re_o$ and $Fr_o$ .

show abstract

Section: Discussionsupporting

confidence: 66%

“…(2020) and the results have been validated in Talluru et al. (2021) and Milton-McGurk et al. (2021).…”

Section: Methodsmentioning

confidence: 59%

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Entrainment and dilution in a fountain top

2022

Self Cite

View full text Add to dashboard Cite

show abstract

“…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%

Characterising entrainment in fountains and negatively buoyant jets

et al. 2022

Self Cite

View full text Add to dashboard Cite

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.

show abstract

“…13 More recently, PIV and planar laser induced fluorescence (PLIF) have been used to simultaneously measure the velocity and scalar concentration fields 22 and to give a first description of the turbulent structure. 23 However, additional experimental datasets and interpretations are needed to understand (i) the complex interaction between the upflow and the counterflow and (ii) the phenomena related to the momentum and mass exchanges.…”

Section: Introductionmentioning

confidence: 99%

Velocity and density measurements in forced fountains with negative buoyancy

2021

View full text Add to dashboard Cite

In fluid mechanics, fountains take place when a source fluid is driven by its own momentum into a surrounding ambient fluid, and it is counterbalanced by buoyancy. These phenomena are largely encountered in nature and human activities. Despite the numerous studies on the subject, few experimental data are available about the internal structure of turbulent fountains. Here, we present a set of laboratory experiments with the aim to (i) get direct velocity and density measurements of fountains in a controlled environment and (ii) obtain insights about the basic physics of the phenomenon. The results concern the characteristics of the mean and turbulent flow: we report the analysis of the turbulent kinetic energy, the velocity skewness, and the Reynolds stresses, including a quadrant analysis of the fluctuating velocities. For some tests, the correlation between density and vertical velocity is investigated for both mean and fluctuating values. We have quantified the momentum transport, which is mainly out-downward at the nozzle axis with peaks at the mean rise height, where also maximum levels of the buoyancy and mass fluxes are present. The ability of acoustic Doppler current profilers to identify the rise height of the fountain and to measure the velocity field is also discussed.

show abstract

Turbulence structure of neutral and negatively buoyant jets

Abstract: Abstract

Cited by 15 publications

References 39 publications

Entrainment and dilution in a fountain top

Entrainment and dilution in a fountain top

Characterising entrainment in fountains and negatively buoyant jets

Velocity and density measurements in forced fountains with negative buoyancy

Contact Info

Product

Resources

About