Vertical Buoyant Jet Research Articles

Development of a Temperature Distribution Measurement System for Transmission Oil for Transportation Equipment

In this study, an optical sensor using thermo-sensitive phosphor and its measurement system for visualizing and measuring the temperature distribution in an arbitrary cross-section of transmission oil using one type of phosphor, whose peak wavelength changes with temperature, is proposed. Because the intensity of the excitation light is gradually attenuated by the scattering of the laser light owing to microscopic impurities in the oil, we attempted to reduce the scattering effect by increasing the excitation light wavelength. Therefore, Pyrromethene 597 was selected as the optical sensor using thermo-sensitive phosphor, and a DPSS (Diode Pumped Solid State) laser with a wavelength of 532 nm was used as the excitation light. Using this measurement system, we measured the temperature distribution of a vertical buoyant jet of transmission oil and validated the measurement method. In addition, it was shown that this measurement system could be applied to the measurement of the temperature distribution in transmission oil with cavitation foaming.

Mean Flow and Mixing Properties of a Vertical Round Turbulent Buoyant Jet in a Weak Crosscurrent

Mean Flow and Mixing Properties of a Vertical Round Turbulent Buoyant Jet in a Weak Crosscurrent

Using an Adaptive Neuro-Fuzzy Inference System to Predict Dilution Characteristics of Vertical Buoyant Jets Subjected to Lateral Confinement

In order to predict the dilution characteristics of vertical buoyant jets constrained by lateral obstructions, we propose a new method based on a commonly used machine learning algorithm: the adaptive neuro-fuzzy inference system (ANFIS). By using experimental data to train and test the ANFIS model, this study shows that it had better performance than commonly used empirical equations for laterally confined jets and another artificial intelligence technique—genetic programming. The RMSE values of the ANFIS-based model were lower, and the R2 values were higher, compared with those of the empirical equation and genetic programming models. The reduction in RMSE achieved by using ANFIS to replace the empirical equations or genetic programming algorithm exceeded 20%. This research confirms that the ANFIS technique has real potential in the development of effective and accurate models that can be used to estimate the dilution characteristics of a vertical buoyant jet subjected to lateral confinement, providing a new avenue for the prediction of dilution characteristics using artificial intelligence techniques, which can also be utilized for other effluent mixing problems in marine systems.

Multi-spatio-temporal scales PIV in a turbulent buoyant jet discharging in a linearly stratified environment

Time-resolved particle image velocimetry is implemented with a camera array and several laser sheets; this results in a multi-spatio-temporal scale system that is modular and flexible. The setup is optimized to capture global flow features, while locally resolving in space and time near the Kolmogorov scale. The apparatus relies extensively on machine vision CMOS cameras; they are inexpensive and stream to computer hard drive with virtually continuous time-resolved records (up to one hour for the current system). This leads to statistically converged data and also helps in minimizing down time between experimental runs. Details of the implementation and design of experiment are reported.The system instruments a vertical buoyant jet discharging in a linearly stratified environment. Refractive index matched aqueous solutions enable precise optical deployment. The density difference is 3% and the fluids have similar dynamic viscosity. The jet Reynolds number is 2.00×104 and is above the mixing transition. Such flows are typically challenging to instrument and few velocity field data are available to date. Velocity statistics are reported as well as first insights gained from the campaign.

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

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.

Three-Dimensional Numerical Study of Multiple Vertical Buoyant Jets in Stationary Ambient Water

AbstractIn this paper, the mixing and dilution characteristics of vertical buoyant jets discharged from multiport diffusers are studied numerically. The performances of four different turbulence cl...

Evolutionary prediction of multiple vertical buoyant jets in stationary ambient water

Evolutionary prediction of multiple vertical buoyant jets in stationary ambient water

Discharge estimation of submarine springs in the Dead Sea based on velocity or density measurements in proximity to the water surface

AbstractThe Dead Sea is a closed lake, the water level of which is lowering at an alarming rate of about 1 m/year. Factors difficult to determine in its water balance are evaporation and groundwater inflow, some of which emanate as submarine groundwater discharge. A vertical buoyant jet generated by the difference in densities between the groundwater and the Dead Sea brine forms at submarine spring outlets. To characterize this flow field and to determine its volumetric discharge, a system was developed to measure the velocity and density of the ascending submarine groundwater across the center of the stream along several horizontal sections and equidistant depths while divers sampled the spring. This was also undertaken on an artificial submarine spring with a known discharge to determine the quality of the measurements and the accuracy of the method. The underwater widening of the flow is linear and independent of the volumetric spring discharge. The temperature of the Dead Sea brine at lower layers primarily determines the temperature of the surface of the upwelling, produced above the jet flow, as the origin of the main mass of water in the submarine jet flow is Dead Sea brine. Based on the measurements, a model is presented to evaluate the distribution of velocity and solute density in the flow field of an emanating buoyant jet. This model allows the calculation of the volumetric submarine discharge, merely requiring either the maximum flow velocity or the minimal density at a given depth.

Formation of compound droplets during fragmentation of turbulent buoyant oil jet in water

Fragmentation of a vertical buoyant silicone oil jet injected into sugar water is elucidated by refractive index matching and planar laser-induced fluorescence. Compound droplets containing multiple water droplets, some with smaller oil droplets, form regularly at jet Reynolds numbers of $Re=1358$ and 2122 and persist for at least up to 30 nozzle diameters. In contrast, they rarely appear at $Re=594$. The origin of some of the encapsulated water droplets can be traced back to the entrained water ligaments during the initial roll-up of Kelvin–Helmholtz vortices. Analysis using random forest-based procedures shows that the fraction of compound droplets does not vary significantly with $Re$, but increases rapidly with droplet diameter, reaching 78 % for 2 mm droplets. Consequently, the size distributions of compound droplets have peaks that increase in magnitude and shift to a lower diameter with increasing $Re$. On average, the interior pockets raise the oil–water interfacial area by 15 %, increasing with diameter and axial location. Also, while the oil droplets are deformed by the jet’s shear field, the interior interfaces remain nearly spherical, consistent with prior studies of the deformation of isolated compound droplets for relevant capillary numbers and viscosity ratio.

Boundary Effects of Vertical Buoyant Jets in a Stagnant Fluid in a Crossflow

This study includes an experimental study of a buoyant jet in an open channel. For this reason experiments to measure the mean axial velocity at the centreline of a buoyant jet which is discharged vertically upwards from a source, into a denser fluid (water) contained in an open channel a) without flow and b) into flowing environment, were performed. The presence of a buoyant jet is studied experimentally using 2D Particle Image Velocimetrer (PIV). For the flow visualization of the buoyant jet, the water, was dyed with either rhodamin (red color) or fluorescein (green color), aiming to the best appearance of the buoyant jet field. The velocity fields of the buoyant jet were determined with the analysis of a lot of pairs of photographs in each experiment. These fields were used to quantify the behaviour of the buoyant jet in the surrounding fluid (salt water) with several densities and flow depths. Also were used to quantify the different behaviour of the buoyant jet into flowing environment in comparison to the behaviour of the buoyant jet without flow. Results show that the depth and density of salt water can affect the flow dynamics. Flow velocity is reduced with the increase of the depth of salt water, due to the proximity to the free surface, while an increase in the salt density increase the buoyant forces and hence the velocity rate. Also the presence of salt water can affect the flow dynamics of the buoyant jet in different way into flowing environment in comparison to the buoyant jet without flow.

Multigene Genetic-Programming-Based Models for Initial Dilution of Laterally Confined Vertical Buoyant Jets

A new approach based on the multigene genetic-programming (MGGP) technique is proposed to predict initial dilution of vertical buoyant jets subjected to lateral confinement. The models are trained and tested using experimental data, and the good matches demonstrate the generalization and predictive capabilities of the evolved MGGP-based models. The best Pareto-optimal MGGP-based model is also compared with the model evolved using a single-gene genetic-programming (SGGP) algorithm and an existing regression-based empirical equation. The comparisons reveal the superiority of the MGGP-based model. This study confirms that the MGGP technique is promising in evolving an explicit, accurate, and compact model, and the developed models can be employed to estimate effectively and efficiently the dilution properties of a laterally confined vertical buoyant jet.

Flow patterns of vertical plane thermal buoyant jet in shallow water

A heated plane water jet impinging vertically onto free water surface has been numerically studied based on large eddy simulation method coupled with the volume of fluid approach. The Boussinesq approximation is adopted to simulate the effect of buoyancy. Results showed that there exist two flow patterns for the plane thermal buoyant jet, which are the stable impinging flow pattern and the flapping impinging flow pattern. Distinct temperature stratification can be found in the stable impinging flow pattern, while it disappears in the flapping impinging flow pattern.

Numerical Simulation of Vertical Buoyant Wall Jet Discharged into a Linearly Stratified Environment

AbstractResults are presented from a numerical simulation to investigate the vertical buoyant wall jet discharged into a linearly stratified environment. A tracer transport model considering densit...

Experimental and numerical investigation of turbulent jets issuing through a realistic pipeline geometry: Asymmetry effects for air, helium, and hydrogen

Experiments and numerical simulations were conducted to investigate the dispersion of turbulent jets issuing from realistic pipe geometries. The effect of jet densities and Reynolds numbers on vertical buoyant jets were investigated, as they emerged from the side wall of a circular pipe, through a round orifice. Particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) techniques were employed simultaneously to provide time-averaged flow velocity and concentrations fields. Large eddy simulation (LES) was applied to provide further detail with regards to the three-dimensionality of air, helium, and hydrogen jets. These jets were always asymmetric and found to deflect about the vertical axis. The deflection was influenced by buoyancy, where heavier gases deflected more than lighter gases. Significant turbulent mixing was also observed in the near field. The jets from realistic pipe geometries experienced faster velocity decay and asymmetric jet spreading compared to round jets. These findings indicate that conventional round jet assumptions are, to some extent, inadequate to predict gas concentration, entrainment rates and, consequently, the extent of the flammability envelope of realistic gas leaks.

Large eddy simulation of a vertical buoyant jet in a vegetated channel

Predicting the flow and dilution of a buoyant jet in vegetated regions is widely applied in ecology and engineering practices. Large eddy simulation is used to study a vertical buoyant jet that was injected into a cross-flow with emergent rigid vegetation. This simulation successfully reproduces the jet behaviour and the spatio-temporal evolution of vortex structures of turbulent jet with vegetation. The time-averaged velocity and temperature field are compared with the experimental results. The similarities and differences between the tests with and without vegetation are also studied. The existence of vegetation diminishes the channel velocity, thereby significantly increasing the jet penetration height and dilution. Spectral analysis is used to investigate the lengths of the vortices corresponding to the dominant frequency at different locations in the flow field.

Numerical Modeling of Vertical Buoyant Jets Subjected to Lateral Confinement

AbstractThe near-field flow and mixing properties of vertical buoyant jets subjected to lateral confinement are studied numerically for different cases, including different confinement indexes and ...

Experimental and numerical study on density stratification erosion phenomena with a vertical buoyant jet in a small vessel

The Japan Atomic Energy Agency (JAEA) has started the ROSA-SA project to investigate thermal hydraulic phenomena in a reactor containment vessel during a severe accident. The hydrogen distribution in the vessel is one of significant safety issues in discussing a potential of hydrogen combustion in the containment. Density stratification and its break-up are important phenomena affecting the hydrogen distribution. This paper focuses on a density stratification erosion and break-up mechanism with a vertical buoyant jet promoting the turbulent helium transport. Small scale experiment and computational fluid dynamics (CFD) analyses were carried out for investigating this phenomena. In the experiment, a rectangular vessel made with acrylic plates with a width of 1.5m, a length of 1.5m and a height of 1.8m was used for visualizing flow field with particle image velocimetry (PIV) system. The quadrupole mass spectrometer (QMS) system with a multiport rotating valve was applied for measuring gaseous concentration at 20 elevation points. In CFD analysis with OpenFOAM, two typical well-used turbulence models were used: low-Reynolds number type k–ɛ model and SST k–ω model, with a turbulence model modification to consider the buoyant effect in the stratification. As a result, the stratification erosion in the CFD analyses with the modified turbulence model agreed well with the experimental data, indicating importance of the turbulence damping by the buoyant effect.

RANS analyses on erosion behavior of density stratification consisted of helium–air mixture gas by a low momentum vertical buoyant jet in the PANDA test facility, the third international benchmark exercise (IBE-3)

Density stratification in the reactor containment vessel is an important phenomenon on an issue of hydrogen safety. The Japan Atomic Energy Agency (JAEA) has started the ROSA-SA project on containment thermal hydraulics. As a part of the activity, we participated in the third international CFD benchmark exercise (IBE-3) focused on density stratification erosion by a vertical buoyant jet in containment vessel. This paper shows our approach for the IBE-3, focusing on the turbulence transport phenomena in eroding the density stratification and introducing modified turbulence models for improvement of the CFD analyses. For this analysis, we modified the CFD code OpenFOAM by using two turbulence models; the Kato and Launder modification to estimate turbulent kinetic energy production around a stagnation point, and the Katsuki model to consider turbulence damping in density stratification. As a result, the modified code predicted well the experimental data. The importance of turbulence transport modeling is also discussed using the calculation results.

Axisymmetric Underflows from Impinging Buoyant Jets of Dense Cohesive Particle-Laden Fluids

AbstractUnderflows generated from the impingement of descending dense cohesive particle-laden buoyant jets on a horizontal bottom of a water body were investigated theoretically and experimentally. Laboratory experiments were conducted by discharging fluid mud (suspension of cohesive clay particles in water) at a constant volume flow rate from a submerged vertical pipe into a body of water. The experiments involved a wide range of initial parameters (e.g., height of the discharge pipe from the bottom, flow rate, and concentration of the fluid mud at the time of discharge). The discharged fluid mud descended as vertical buoyant jets and flowed away as axisymmetric underflows after impinging on the bottom. The underflows exhibited two well-documented propagation phases: (1) a radial momentum-driven wall jet phase near the impingement region, and (2) an inertial gravity current phase after the completion of the wall jet phase. Experiments revealed that, depending on the initial discharge parameters, underflo...

Experimental investigation on behavior of multiple vertical buoyant jets discharged into a stagnant ambient

The behavior of merging buoyant jets discharged from uni-directional diffuser has been examined considering the interaction of individual axi-symmetric jets. Some series of experiments have been performed to define the range of merging transition based on the variations of local flow properties. The properties for the large eddies on the boundaries; passing frequency, vortex spacing, and Strouhal number, are also measured to investigate the evolution of individual jets to a merged flow. The results of this study show that the local flow properties change from those of axi-symmetric to merged flow over a merging transition where b/ps = 0.3 to 1.2. The flapping motion is observed as the individual jets get merged with neighboring ones. After the merging transition (b/ps = 0.3 to 1.2), the flows show a typical behavior of plane flows with a constant value of Strouhal number.