Negatively Buoyant Jets

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

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

Abstract. 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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On the near field behavior of inclined negatively buoyant jets

On the near field behavior of inclined negatively buoyant jets

Abstract. We have performed an experimental campaign in the laboratory on the near field behavior of inclined negatively buoyant jets, issuing from a circular sharp-edged orifice, in order to investigate the symmetry properties of this phenomenon. The velocity measurements were obtained via a non intrusive image analysis technique, namely Feature Tracking Velocimetry. We present here both first and second order statistics, showing that the asymmetry of inclined negatively buoyant jets cannot be considered only a far field feature of this phenomenon, as it arises very close to the release point.
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Laboratory experiments on the interaction between inclined negatively buoyant jets and regular waves

Laboratory experiments on the interaction between inclined negatively buoyant jets and regular waves

The behavior of Inclined Negatively Buoyant Jets (INBJs) released into a wavy environment was analyzed from a statistical point of view, both considering the global phenomenon and its single phases. Analysis on the mean concentration fields allowed determining the deformations that the wave motion causes on INBJs: these, although being forced to oscillate, preserve their identity close to the origin, whilst further from their origin the INBJs are split into two separate branches that, eventually, fuse together before sinking to the bottom. The points of maximum height and the impact point (where the axis returns to the same level of the jet origin) do not rotate around the position they have in a stagnant environment, as it happens in vertical or horizontal simple jets, but always stay below it: the former is more biased by the wave period whilst the latter by the wave amplitude. This decrement increases as the wave period and amplitude increase and it is likely due to the interaction between two causes: one is the split into two branches of the central region of INBJs that, increasing the interchange surface between the jet and the external fluid, speeds up the dissipation of the initial momentum; the other is the rotational movement the waves impose to the central region of INBJs, that tends to slow its rising down. The splitting in two of INBJs under wave motion increases with low densimetric Froude numbers. Moreover, when Froude decreases, the concentration profiles, transversal to the jet axis, have a lower widening and tend to be more symmetrical: this is due to the larger mixing caused by the rotation, imposed by the wave motion on the descending branch of the INBJ, which contributes to spread more uniformly the discharged fluid. Analyses on variance and on the profile of concentration have confirmed that the wave motion increases the interface available for mixing and so allows amplifying the entrainment, extending the path available for mixing and, consequently, increasing the dilution.
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Experimental Studies for the characterization of the mixing processes in negative buoyant jets

Experimental Studies for the characterization of the mixing processes in negative buoyant jets

The behaviour of Negatively Buoyant Jets, released from a sharp-edged orifice, was investigating using an Feature Tracking Velocimetry, an original and efficient image analysis technique Mean velocity fields and second order statistics were used to characterize the behaviour of this phenomenon and to assess its dependence on some jet parameters. Observed lack of axial symmetric behaviour points out that caution must be observed when using integral solutions or applying numerical codes based on the hypothesis of axial symmetry.

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Buoyant jets with two and three dimensional trajectories

Buoyant jets with two and three dimensional trajectories

With the increase in the demand for clean water as well as decreasing costs for the desalination process, desalination plants are becoming an increasingly viable option as a supplementary reliable main water supply for many communities. The effluent from desalination plants has relatively high salinity concentrations. Discharging the effluent into less dense surrounding fluid makes the effluent fall rather than rise. If the ambient motion is relatively small or non-existent the discharge essentially becomes a negatively buoyant jet. Except for the vertical discharge configuration, the negatively buoyant jet has not received a great deal of attention. Past experimental investigators have primarily studied the behaviour of the discharge with a 60° angle, and to a lesser extent the 30° and 45°. The experimental results have focused on the rise height of the flow, the distance from the point of release to the impact point (the point at which the flow returns to the source height), and the dilution at the impact point. Widening the scope of the investigation into the behaviour of the negatively buoyant jets (including a range of discharge angles and determining spread and dilution data along the trajectory of the flow), will increase the knowledge of the mixing characteristics of these flows. This understanding can eventually lead to more effective discharge techniques.
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The stability of buoyant bubbles in the atmospheres of galaxy clusters

The stability of buoyant bubbles in the atmospheres of galaxy clusters

The buoyant rise of hot plasma bubbles inflated by AGN outflows in galaxy clusters can heat the cluster gas and thereby compensate radiative energy losses of this material. Numerical simulations of this effect often show the complete disruption of the bubbles followed by the mixing of the bubble material with the surrounding cluster gas due to fluid instabilities on the bubble surface. This prediction is inconsistent with the observations of apparently coherent bubble structures in clusters. We derive a general description in the linear regime of the growth of instabilities on the surface between two fluids under the influence of a gravitational field, viscosity, surface tension provided by a magnetic field and relative motion of the two fluids with respect to each other. We demonstrate that Kelvin-Helmholtz instabilities are always suppressed, if the fluids are viscous. They are also suppressed in the inviscid case for fluids of very different mass densities. We show that the effects of shear viscosity as well as a magnetic fields in the cluster gas can prevent the growth of Rayleigh-Taylor instabilities on relevant scale lengths. R-T instabilities on pc-scales are suppressed even if the kinematic viscosity of the cluster gas is reduced by two orders of magnitude compared to the value given by Spitzer for a fully ionised, unmagnetised gas. Similarly, magnetic fields exceeding a few µG result in an effective surface tension preventing the disruption of bubbles. For more massive clusters, instabilities on the bubble surface grow faster. This may explain the absence of thermal gas in the north-west bubble observed in the Perseus cluster compared to the apparently more disrupted bubbles in the Virgo cluster.
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Liquid Fuel Combustion in a Cross-Flow of Multiple Opposing Gaseous Fuel Jets

Liquid Fuel Combustion in a Cross-Flow of Multiple Opposing Gaseous Fuel Jets

Abstract :- An Investigation on the effect of cross flow of multiple opposing gaseous fuel jets on liquid fuel burning was performed that could be retrofit into an existing or future manufactured gas turbine engines to provide an energy solution to problem of growing levels of carbon emissions. The combustion chamber was provided with dual fuel burner, and experimentally burn liquid fuel in a cross flow of gaseous fuel. While the air was co-axially introduced in a double swirl flow field, the combustion efficiency and flame length were recorded in conjunction with varying the number of opposing jets. Results verified that the average temperature of the product gases has been generally improved by 21.8 ~ 52.1 % than the original case of diesel oil burning. Local temperature drop, just after entering cross flow gases, decreased with increasing the number of opposing jets as a result of lower mass flux, which in turn affected the shear rates and mixing between hot gases and cold cross flow gaseous fuel. However, overall fuel to air ratio has been increased with same quantity of air, the cross flow interaction made a clearer exhaust than without this cross flow by visual exhaust observation. The analysis of exhaust emissions indicated using cross flow technique generally, has a positive effect in concentration of Carbon Monoxides (CO) by 6.7~ 68.4 % and Nitrogen Monoxide (NO) by 15.7 ~ 63.1 % and percentage of Hydrocarbons (CxHy) in the product gases by 26.6 ~ 46.6 %.
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Photoproduction of Jets

Photoproduction of Jets

The photoproduction of jets at HERA is proving to be a very fruitful process in which to study strong interactions. Aspects of QCD which are being investigated in- clude the partonic structure of both the proton and the photon, the internal structure of jets, and the dynamics of jet production. I will omit jet production in association with prompt photons, charm and rapidity gaps - these reactions are covered in other contributions.

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The Innermost Regions of Relativistic Jets: Wrapping Up the Enigma

The Innermost Regions of Relativistic Jets: Wrapping Up the Enigma

Another scandal exposed at the conference involves disagreement about the geometry of the magnetic field of jets on parsec scales. While apparently coherent ro- tations of polarization vectors have been used as evidence for the helical fields predicted by theorists closer to the black hole, there are reasons to expect a residual helical field, the chaos of turbulence, longitudinal fields stretched out by velocity shear, or either transverse or oblique fields from shock compression. The battle waged at the meet- ing, depicted in Figure 5, pitted helical (proponent: Denise Gabuzda) versus turbulent (which I defended) magnetic geometries. Points favoring helical fields include the need for this geometry to explain the acceleration and colli- mation of jets, combined with the finding that many jets continue to accelerate on parsec scales; the ability to ex- plain rotations of polarization vectors observed in a num- ber of blazars, as well as the kinks and wave-like struc- ture reported by Marshall Cohen in BL Lacertae; and the prediction of Faraday rotation gradients across the jet, which have been measured by Denise Gabuzda, Shane O’Sullivan, Evgeniya Kravchenko, Eoin Murphy, and Mo- hammad Zamaninasab. But I counter that helical fields have a hard time explaining that the degree of linear polar- ization is usually both low and variable, and that the EVPA fluctuates, in bright blazars.
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'The potential of buoyant aircraft for passenger transport'

'The potential of buoyant aircraft for passenger transport'

None of the more ambitious projects from this era came to fruition, although progress was made in enhancing and enlarging smaller craft. The mid-to-late 1990s saw a second revival of interest in buoyant aircraft. A wide variety of proposals were put forward and, although some again failed, others continue at the time of writing. It is, however, undeniable that much remains to be done, and that considerable uncertainty must continue to characterise any review of the future potential of this mode. Table 1 summarises some current or recent projects. It also outlines the notional craft design used for analysis in the field of passenger transport, the characteristics of which have been projected on the basis of a previous study (3). The Zeppelin N 07 is one of the first of the recent attempts to produce a modern airship, and is now in regular sightseeing service. It is likely to prove too small for scheduled transport, but outline plans exist for larger craft, up to 84 passenger seats.
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Structure and Stability of Buoyant Diffusion Flames

Structure and Stability of Buoyant Diffusion Flames

Neutral stability and amplification contours for symmetric buoyant diffusion flame using Boussinesq approximation.. Wave number-Reynolds number diagram with global nondimensionalisation.[r]

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Dynamic Response Analysis of Stiffened Triceratops Under Regular Waves

Dynamic Response Analysis of Stiffened Triceratops Under Regular Waves

Buoyant legs are designed as stiffened cylinders since they have to resist both axial stress and bending moment caused by lateral forces. Stiffeners are welded to the shell, this enhances their lateral resistance. In addition to ring stiffeners, longitudinal stiffeners called as stringer stiffeners are also provided at equal spacing, both externally and internally. The operational advantages of the structural configuration include its reduced deck response and good re- centering capability.

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Jet noise source distribution for coplanar nozzles: experiments and predictions

Jet noise source distribution for coplanar nozzles: experiments and predictions

Changes in the primary and secondary flow velocities at a fixed velocity ratio can also alter the source distribution. It has been shown before that by increasing the efflux velocity the potential core length increases. For instance, the potential core length for an unheated single flow jet can be found from L c = 6.25(1 − 0.16M j ) − 1 D J [3]. This leads to a slightly longer potential core and therefore a larger interaction surface between the secondary shear flow and the ambient medium. This lessens the effect of the downstream high and intermediate frequency sources. Comparison of figures 5 and 6 with figures 8 and 9 reveals that in the higher speed coplanar jets the source region is more compact and the source distribution is more similar to that of an equivalent single flow jet.
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Standard Model measurements with the ATLAS detector

Standard Model measurements with the ATLAS detector

The successful operation of the Large Hadron Collider (LHC) during the past three years allowed to explore particle interaction in a new energy regime. Various Standard Model measurements have been performed in proton-proton collisions at a centre-of-mass energy of √ s = 7 and 8 TeV using the ATLAS detector [1] at the LHC. These allow for precision tests of the electroweak dynamics of the Standard Model, but also challenge next-to-next-to-leading-order predictions. Di ff erences between measurements and Standard Model predictions could prove evidence for new phenomena. Recent Quantum Chromo Dynamics (QCD) results highlight the importance of precision QCD measurements for improving state-of-the-art theoretical tools and searching for new physics. A selection of the latest results of electroweak measurements, W/Z production in association with jets, jet physics and soft QCD is reported. These consist of the measurement of the WW cross section, first evidence of the electroweak production of W ± W ± j j, and electroweak Z j j production. Measurements are in general found to be well described by the Standard Model predictions. Measurements of differential produc- tion cross sections of a Z boson in association with b-jets, the production cross section of the W boson in association with jets as well as the ratio of the production cross sections for W and Z bosons in association with jets are presented. The measurements are compared to next-to-leading-order pertur- bative QCD calculations and to predictions from different Monte Carlo (MC) generators implement- ing leading-order matrix elements supplemented by parton showers. Various inclusive, differential or double differential jet measurements are presented. The dominant experimental uncertainty on these measurements comes from the jet energy scale. Next-to-leading order QCD calculations corrected to account for non-perturbative e ff ects are compared to the measurements. A good agreement between the data and the theoretical predictions based on most of the global parton distribution functions is found over the full kinematic range, covering almost seven orders of magnitude in the measured cross-section values. A measurement of charged-particle distributions sensitive to the properties of
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Heavy Flavour in Jets and Azimuthal Correlations

Heavy Flavour in Jets and Azimuthal Correlations

Over the course of the work done for this project, we focused on two analyses. The goal of both anal- yses is to investigate bottom quark jet effects, but for the first analysis we focused on identifying elec- trons from semi-leptonic decays in the EMCal detector and producing an azimuthal correlation plot with hadrons in the whole detector acceptance. For the second analysis, an extension of the first, we at- tempted to include full jet reconstruction with our identified electrons to compare jets originating from heavy quarks to those originating from light quarks and gluons. In order to do this, a way to discriminate the two jet populations was devised and several variables pertaining to the jets’ qualities were calculated. We use two trigger conditions across both analyses. The first is simply minimum bias conditions which is defined by particle hits in the T0 and V0 detectors, considered the minimum interaction required to signify a collision. Additionally we use any event satisfying an energy threshold in the EMCal to extend our energy range.
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On Faraday waves and jets

On Faraday waves and jets

In the following experiment the camera resolution was again of small width, 512 × 48 pixels while the frame rate was smaller at 125f ps. We chose p = 1.04 which corresponds to 8.400 and 8.303Hz in water and sunflower oil respec- tively. At different sweep rates the amplitude is gradually increased and again decreased. Also, the intervals slightly varied to determine if this was a fac- tor, but we did not find significant influence, as long as all regimes are passed through. As we know the excitation as a function of the camera time when can relate it to the wave height. As mentioned before there is some fluctuation on the forcing signal. A result is plotted in figure 4.17 for the slowest sweep rate of 0.5 · 10 −3 gs −1 for the interval 0.01 ≤ f ≤ 0.30 in water. Most notably are a few jets at the transition from a solid-body to a standing wave state. The results are combined in figures 4.18 and 4.18 where the transitions locations are denoted. The direction of the sweeps is from bottom to top and this is how one should read the plots. For every rate there are three runs for water and two for sunflower oil.
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Stationary relativistic jets

Stationary relativistic jets

Our approach is similar to ‘marching’ - we compute so- lution for a downstream jet cross-section using only the previously found solutions for upstream cross-sections. Strictly speaking, this requires the flow to be super-sonic for unmagnetized jets and super-fast-magnetosonic for magnetized ones (Wilson and Falle ; Dubal and Pan- tano ). However, in our derivations we never had to utilize this condition. This suggests that it is not required when we wish to find only approximate solutions. For ex- ample, one may argue that the fact that information can propagate upstream does not necessarily imply that this always has a strong effect on the flow - the upstream- propagating waves could be rather weak. If so, we may still apply our method to jets where the supersonic con- dition is not fully satisfied, but we always need to check that the conditions ()-() of our approximation hold for obtained solutions.
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Eruptions and jets in the Sun

Eruptions and jets in the Sun

As mentioned already in Section 2.2, we should highlight that our numerical model does not include thermal conduction and radiative losses in the energy equation. This causes the heat to be localised, resulting in a higher temperature at various places, such as in regions of strong current sheets. However, we believe that the overall dynamical behaviour of the system (e.g. the onset of recurrent eruptive jets and their mechanism) will not be affected dramatically, by the inclusion of either heat conduction or radiation. To some extent, our hypothesis has been partially confirmed by Fang et al. (2014), who showed that the inclusion of thermal conduction in the energy equation in similar experiments, leads to the ejection of only a small amount of extra mass (not more than 10%, compared to the non-conductive case) into the corona during the emission of the “blowout” jets. Otherwise, they showed that the temporal/spatial evolution of the jets in the conductive and non-conductive cases is very similar.
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A Comparison between steady jets and synthetic jets at low Reynolds numbers

A Comparison between steady jets and synthetic jets at low Reynolds numbers

The primary advantage of the synthetic jet is its zero-net- mass flux nature, which eliminates the need for plumbing, and, when applied to a base flow (one of the primary uses for synthetic jets is in vectoring a main steady flow) results in unique effects not possible with steady or pulsed suction or blowing. The synthetic jet can easily be integrated into complex geometries, requires relatively low operating power, is simple to design and fabricate, and unlike traditional fans or steady jets, it does not require external ducting.

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CFD Simulation of Impinging Jet Flows and Boiling Heat Transfer

CFD Simulation of Impinging Jet Flows and Boiling Heat Transfer

124 In the current study, numerical simulations were carried out to investigate the behaviour of impinging jets with different flow configurations. Steady and unsteady analyses as well as adiabatic and non-adiabatic cases were analyzed. The study was divided into three parts. In the first part, the effect of nozzle stand- off distance on mean flow parameters was analyzed using RANS simulations. In the second section, an unsteady simulation was performed to obtain the time history of the flow parameters in an impinging jet with large stand-off distance. Finally, a CFD model was developed for the analysis of boiling heat transfer in an impinging jet using OpenFOAM source code. The significant contributions of this research are summarized below.
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