An Investigation on the Effects of Different Stratifications on 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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Isothermal free jets in high-temperature surroundings

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/0954406211401488 ◽

2011 ◽

Vol 225 (8) ◽

pp. 1913-1918 ◽

Cited By ~ 1

Author(s):

M A Azim

Keyword(s):

High Temperature ◽

Dynamical Behaviour ◽

Flow Dynamics ◽

Governing Equations ◽

Buoyant Jet ◽

Buoyant Jets ◽

Free Jets ◽

Tridiagonal Matrix Algorithm ◽

Negatively Buoyant ◽

Negatively Buoyant Jets

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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Simulation of temperature influence on flow pattern and residence time in a detention tank

Hydrology Research ◽

10.2166/nh.2006.0005 ◽

2006 ◽

Vol 37 (1) ◽

pp. 53-68 ◽

Cited By ~ 3

Author(s):

Åsa Adamsson ◽

Lars Bergdahl

Keyword(s):

Flow Pattern ◽

Residence Time ◽

Scale Model ◽

Buoyant Jet ◽

Buoyant Jets ◽

Densimetric Froude Number ◽

Detention Tank ◽

Negatively Buoyant Jet ◽

Neutrally Buoyant ◽

Negatively Buoyant

Three-dimensional simulations were used to model how a temperature difference between the incoming water and tank water influences the flow pattern and residence time in a detention tank. Buoyant, neutrally buoyant and negatively buoyant incoming jets were simulated. The simulations were compared with measurements for neutrally buoyant jets in a large-scale model of a detention tank (13 × 9×1 m). The results show that a negatively buoyant jet gives slightly less effective volume, defined as the time when 50% of added tracer has passed the outlet divided by the nominal residence time, than a neutrally buoyant jet. The flow pattern for a negatively buoyant jet at low densimetric Froude numbers consists of a current that travels along the bottom towards the outlet and a counter current at the surface towards the inlet, while the neutrally buoyant jet excites a surface jet with two large eddies on each side of the jet. This implies that the short-circuiting will decrease when a negatively buoyant jet at low densimetric Froude number occurs in the tank. The difference between the flow pattern excited by a buoyant jet and a neutrally buoyant jet is small.

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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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