Isothermal free jets in high-temperature surroundings

Two types of isothermal free jets, named positively and negatively buoyant, have been studied numerically to discern the effect of surrounding temperatures on their flow dynamics. Turbulence closure in those jets was achieved by standard k - ε model. The governing equations were solved using Implicit θ-Scheme and Tridiagonal Matrix Algorithm. Calculations were made for the jets having constant temperature at 20 °C and by varying surrounding temperatures from 20°C to 1000°C. It is clear that negatively buoyant jets but not the positively buoyant jets are nearly invariant to the change in surrounding temperatures compared to non-buoyant jet. Change in fluid dynamical behaviour of positively buoyant jets due to surrounding temperature change seems promising as it may offer the advantages of fuel jets in high-temperature air combustion.

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An Investigation on the Effects of Different Stratifications on Negatively Buoyant Jets

EPJ Web of Conferences ◽

10.1051/epjconf/201818002025 ◽

2018 ◽

Vol 180 ◽

pp. 02025 ◽

Cited By ~ 1

Author(s):

Simone Ferrari ◽

Maria Grazia Badas ◽

Giorgio Querzoli

Keyword(s):

Lower Boundary ◽

Marine Species ◽

Laboratory Model ◽

Buoyant Jet ◽

Buoyant Jets ◽

Sea Bottom ◽

Desalination Plants ◽

Negatively Buoyant Jet ◽

Negatively Buoyant ◽

Negatively Buoyant Jets

Negatively buoyant jets develop when fluids are released upwards into a lighter fluid or, vice versa, downwards into a heavier fluid. There are many engineering applications, such as the discharge, via submerged outfalls, of brine from desalination plants into the sea. Some concerns are raised about the potential negative environmental impacts of this discharge. The increase in salinity is the major cause for environmental impact, as it is very harmful to many marine species. The diffusers for brine discharge are typically inclined upwards, to increase the path before the brine reaches the sea bottom, as it tends to fall downwards driven by negative buoyancy. The negatively buoyant jet that develops conserves axisymmetry only when released vertically, so that it is not possible to use the well-known equations for axisymmetric jets. The main target of this paper is to investigate on a laboratory model the effects of different stratifications on the features of negatively buoyant jets. This has been done via a LIF (Light Induced Fluorescence) technique, testing various release angles on the horizontal and densimetric Froude numbers. Except for the initial stage, a different widening rate for the upper boundary and the lower boundary has been highlighted.

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Vertical Round Buoyant Jets and Fountains in a Linearly, Density-Stratified Fluid

Fluids ◽

10.3390/fluids5040232 ◽

2020 ◽

Vol 5 (4) ◽

pp. 232

Author(s):

Panos N. Papanicolaou ◽

George C. Stamoulis

Keyword(s):

Steady State ◽

Laboratory Experiments ◽

Coefficient Function ◽

Buoyant Jets ◽

Asymptotic Values ◽

Entrainment Coefficient ◽

Source Level ◽

The Mean ◽

Negatively Buoyant ◽

Negatively Buoyant Jets

Turbulent round buoyant jets and fountains issuing vertically into a linearly density-stratified calm ambient have been investigated in a series of laboratory experiments. The terminal (steady-state) height of rise and the mean elevation of subsequent horizontal spreading have been measured in positively buoyant jets (at source level), including pure momentum jets and plumes, as well in momentum-driven negatively buoyant jets (fountains). The results from experiments confirmed the asymptotic analysis that was based on dimensional arguments. The normalized terminal height and spreading elevation with respect to the elevation of injection of momentum-driven (positively) buoyant jets and fountains attained the same asymptotic values. The numerical results from the solution of entrainment equations, using an improved entrainment coefficient function, confirmed the results related to buoyancy dominant flows (plumes), while their predictions in momentum-driven flows were quite low if compared to measurements.

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