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

Fluids ◽  
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.

On the entrainment coefficient in negatively buoyant jets

2008 ◽  
Vol 614 ◽  
pp. 447-470 ◽  
Author(s):  
PANOS N. PAPANICOLAOU ◽  
ILIAS G. PAPAKONSTANTIS ◽  
GEORGE C. CHRISTODOULOU
Keyword(s):  
Self Similarity ◽  
Distribution Models ◽  
Cross Sectional ◽  
Buoyant Jets ◽  
Wide Range ◽  
Model Predictions ◽  
Entrainment Coefficient ◽  
Negative Buoyancy ◽  
Negatively Buoyant ◽  
Negatively Buoyant Jets

Integral models proposed to simulate positively buoyant jets are used to model jets with negative or reversing buoyancy issuing into a calm, homogeneous or density-stratified environment. On the basis of the self-similarity assumption, ‘top hat’ and Gaussian cross-sectional distributions are employed for concentration and velocity. The entrainment coefficient is considered to vary with the local Richardson number, between the asymptotic values for simple jets and plumes, estimated from earlier experiments in positively buoyant jets. Top-hat and Gaussian distribution models are employed in a wide range of experimental data on negatively buoyant jets, issuing vertically or at an angle into a calm homogeneous ambient, and on jets with reversing buoyancy, discharging into a calm, density-stratified fluid. It is found that geometrical characteristics such as the terminal (steady state) height of rise, the spreading elevation in stratified ambient and the distance to the point of impingement are considerably underestimated, resulting in lower dilution rates at the point of impingement, especially when the Gaussian formulation is applied. Reduction of the entrainment coefficient in the jet-like flow regime improves model predictions, indicating that the negative buoyancy reduces the entrainment in momentum-driven, negatively buoyant jets.

scholarly journals Positively and Negatively Round Turbulent Buoyant Jets into Homogeneous Calm Ambient

Proceedings ◽  
2018 ◽  
Vol 2 (11) ◽  
pp. 572 ◽  
Author(s):  
Anastasia Fragkou ◽  
Panos Papanicolaou
Keyword(s):  
Mathematical Model ◽  
Differential Equations ◽  
Richardson Number ◽  
Nonlinear Differential Equations ◽  
Ambient Fluid ◽  
Buoyant Jets ◽  
First Order ◽  
Entrainment Coefficient ◽  
Negatively Buoyant ◽  
Negatively Buoyant Jets

A mathematical model has been employed to determine the characteristics of Boussinesq round buoyant jets which are injected horizontally or at an angle to horizontal, into a homogeneous, calm ambient. The solution of a system of three conservation first order nonlinear differential equations was obtained with a 4th Runge-Kutta scheme, using an entrainment coefficient which is related to the local Richardson number of the flow. Two types of positively and negatively buoyant jets were investigated (i) those where the buoyancy is a function of salinity henceforth called saline jets, and (ii) those where the buoyancy is a function of the temperature difference between jet and ambient fluid, henceforth called thermal jets.

scholarly journals Vertical Plane Buoyant Jets and Fountains in a Uniform Stagnant Ambient Revisited

2021 ◽  
Author(s):  
Panagiotis Minos ◽  
Panos N. Papanicolaou
Keyword(s):  
Laboratory Experiments ◽  
Flow Direction ◽  
Equations Of Motion ◽  
Vertical Plane ◽  
Closed Form Solution ◽  
Form Solution ◽  
Coefficient Function ◽  
Buoyant Jet ◽  
Buoyant Jets ◽  
Entrainment Coefficient

Abstract Planar, vertical buoyant jets are of particular interest, both for research and practical purposes for being related to the disposal of the effluent from wastewater treatment plants or saline, a by-product from desalination plants into a body of stagnant fluid. Analytical, closed form solution is derived for plane buoyant jets based on a buoyant jet width parameter proposed by List and Imberger (1973), and compares to earlier laboratory experiments satisfactorily. The derived entrainment coefficient as a function of the local Richardson number of the flow, takes two asymptotic values for jet-like and plume-like flows, while in fountains it takes values lower than that in jets. Laboratory experiments were performed to measure the penetration height of vertical plane fountains with initial Froude number in the range 20 to 130 using shadowgraph and Planar Laser Induced Fluorescence (PLIF) techniques. Interest was focused on the maximum and terminal, steady-state penetration height before the flow direction reversed. The flow was found to be in a state of unstable equilibrium, as it deviated from the vertical axis, swinging on either side. The equations of motion have been solved numerically using the derived entrainment coefficient function, and the results are congruent to earlier and present experiment for vertical fountains.

scholarly journals Flow behaviour of negatively buoyant jets in immiscible ambient fluid

2011 ◽  
Vol 52 (1) ◽  
pp. 261-271 ◽  
Author(s):  
A. Geyer ◽  
J. C. Phillips ◽  
M. Mier-Torrecilla ◽  
S. R. Idelsohn ◽  
E. Oñate
Keyword(s):  
Flow Behaviour ◽  
Ambient Fluid ◽  
Buoyant Jets ◽  
Negatively Buoyant ◽  
Negatively Buoyant Jets

scholarly journals On the Effect of Regular Waves on Inclined Negatively Buoyant Jets

Water ◽  
2018 ◽  
Vol 10 (6) ◽  
pp. 726 ◽  
Author(s):  
Simone Ferrari ◽  
Maria Badas ◽  
Giorgio Querzoli
Keyword(s):  
Regular Waves ◽  
Buoyant Jets ◽  
Negatively Buoyant ◽  
Negatively Buoyant Jets

Isothermal free jets in high-temperature surroundings

2011 ◽  
Vol 225 (8) ◽  
pp. 1913-1918 ◽  
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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