Horizontal Buoyant Jet Research Articles

Horizontal buoyant jets into viscoplastic ambient fluids

This study investigates the horizontal injection of a heavy Newtonian fluid into a lighter viscoplastic ambient fluid, in a large reservoir. The flow dynamics is experimentally captured via camera imaging, laser-induced fluorescence, and particle image velocimetry techniques. The flow parameters include various density differences, injection velocities, and ambient fluid viscoplastic properties. Our analysis identifies two key dimensionless numbers, the Froude number (Fr) and the effective viscosity ratio (m), which includes the rheology of the viscoplastic fluid. Our study also examines the effects of these dimensionless numbers on critical jet characteristics, such as bifurcation length, transition length, deviation length, and jet trajectory, and provides correlations using Fr and m, to predict these characteristic lengths. A regime classification based on the bifurcation phenomenon is also presented in the Fr−m plane.

Experimental study, dimensional analysis and an integral model for horizontal buoyant turbulent jet fires under opposing wind

This work demonstrates a comprehensive model for horizontal turbulent jet flame geometries under opposing wind, for which few data or models can be found in the literature. This situation can be a practical scenario of offshore drilling platform with a horizontal flare under opposing wind. The opposing wind pushes the jet flame back, which eventually turns around and upwards, pointing finally downstream in the windward direction. The flame geometries are characterized by four parameters including horizontal length and vertical height from nozzle exit to the location of farthest point that flame envelope could reach before the flame turns around as well as horizontal length and vertical height from nozzle exit to the location of flame tip. Experiments are carried out for horizontal jets discharged from circular nozzles having diameters of 3, 5, 7 and 9 mm and employing propane as fuel with opposing wind speeds from 0.35 to 1.08 m/s. The locations of flame tip and the flame farthest point decrease with increasing opposing wind for a constant heat release rate. Dimensional analysis is derived from a physical model considering the momentum of fuel jet, flame buoyancy due to the flame temperature rise, opposing wind momentum and normalized flow rate at stoichiometric conditions at flame tip. The normalized flame geometry parameters based on the proposed model are well represented by two characteristic length scales derived by accounting for the interaction between excess jet-wind momentum and flame buoyancy as well as that between opposing wind momentum and flame buoyancy. In addition, the normalized mass flow rate at stoichiometric conditions determines the total length of flame trajectory. Moreover, an integral model is deduced by an air entrainment model and top hat profiles for the mass and momentum conservations to predict well the flame geometries of horizontal jet fires under opposing wind.

Projected flame length and flame extension length of horizontal buoyant jet flames

Abstract Jet fires are a type of dangerous fire caused by the sudden release of flammable materials. In this work, propane was used as fuel and released through a 7.15mm and 9.8 mm circular nozzle with the exit velocities were set ranging between 27 and 65 m/s. The data of this study are compared against theoretical measurement and prediction using previously suggested correlation for projected flame length and flame extension length. It was determined, the projected flame length gives a good prediction by using theoretical measurement while for the prediction of flame extension length, an elliptical shape assumption was suitable to be used after impinging point for a horizontal buoyant jet fire.

Hydrodynamics of horizontal heated buoyant jet in linearly stratified fluids

Horizontal buoyant jets in stratified fluids are investigated by employing a computational fluid dynamic model validated by experimental data. The characteristics of time mean flow, turbulence, and entrainment are quantified. We observed that turbulence parameters such as the turbulent kinetic energy, the turbulence dissipation rate, and turbulent viscosity attained their maximum values in the horizontal region. Here, the entrainment coefficient also reaches the maximum due to the instantaneous instability of the flow. The ascent region consists of the acceleration and deceleration stages due to the stratified ambience reversing the sign of buoyancy flux. In the acceleration ascent region, the entrainment coefficient stabilizes around 0.05. In the deceleration stage, the transition of the flow regime from plume- to jet-like regulates the entrainment. At the end of the ascent region, the jet reaches the maximum rise height (Hmax), which can be well predicted by a semiempirical function at a given Richardson number, buoyancy frequency, and Reynolds number. An enhancement of turbulent parameters is observed near the Hmax and could be attributed to overshooting and shearing between the up- and downflow. Analysis of density and velocity profiles shows the heavy fluids on the lower side of the jet core vertically separating from the center fluids, which drifted the velocity profile from a Gauss to a fat-tailed distribution and broke the self-similarity.

Main geometrical features of horizontal buoyant jet fire and associated radiative fraction

AbstractHigh momentum release of jet fire can be very intense, and the released heat can be very high, depending on the source capacity. One of the key parameters in characterizing the jet fire is the radiative fraction. The previous study has correlated the radiative fraction to the source using a Froude number basis. Nevertheless, the flame mechanism and associated geometrical features gave significant effects on the global radiative heat flux to some extent. Therefore, the characterization of the main geometrical features, particularly on jet flame structures at higher momentum release conditions and its correlation with the radiative fraction, are valuable to be investigated. In this work, propane was used as fuel and released through a 9.8 mm circular nozzle with the exit velocities were set ranging between 27 and 65 m/s. It was found that the liftoff length estimation from this work is in a good agreement with the jet fire release under sub‐atmospheric pressure in a vertical orientation. Furthermore, the flame projected length and height were characterized by momentum‐driven length (L m) and buoyancy‐driven height (L b) by the dimensionless characteristics length (Ʌ). The experimental observations indicate that as the Ʌ ≥ 0.0001, the radiative fraction shows a decreasing trend.

A mathematical approach to submerged horizontal buoyant jet trajectory and a criterion for jet flow patterns

This paper focused on the trajectory and flow patterns of submerged horizontal gas jet in stagnant ambient liquid. A rigorous mathematical model for the jet trajectory was developed based on geometric analysis, mass conservation, and momentum. Additional, multiple N2-Water experiments employing binary image processing were designed and performed. The experimental procedures and mathematical derivations are presented here in details. To assess the ability of the mathematical model to predict the jet trajectory, extensive experimental results were extracted for comparison with the mathematical results. The mathematical results were found to be in good agreement with the experimental results. Furthermore, a dimensionless jet spreading angle model was proposed and fitted to the experiment results. A flow pattern transition criterion based on the penetration depth of the buoyant jet in the water was also discussed, distinguishing the gas buoyant jet form bubbly or transitional flow patterns.

Modelling and experimental investigation of horizontal buoyant gas jets injected into stagnant uniform ambient liquid

In this article, an experimental and theoretical study on the buoyant non-condensable gas jet that is injected horizontally into a high-density liquid ambient at different initial conditions is performed. Direct and instantaneous global measurements of the interface were performed using a high-speed photography. The position and motion of the entire gas jet were captured by a high-velocity camera and the images were processed, averaged and analyzed to extract the jet parameters and interface position. In the mathematical model, the rate of entrainment is assumed to be a function of the jet centerline velocity, the ratio of the mean jet and the ambient densities, while the entrainment coefficient depends on the local Froude number at the jet region. An interfacial shear stress acting at the interface between the jet flow and the water ambient in the opposed direction to the main jet momentum flux is considered. The results showed that the model is able to accurately predict the jet parameters: trajectory, spread, jet angles and penetration lengths as well as the jet regimes. An overall good agreement was obtained between the simulation and experimental results over a large range of Froude numbers and jet diameters. The developed model has proven to be an adequate tool to predict the different jet parameters.

Flow patterns and mixing characteristics of horizontal buoyant jets at low and moderate Reynolds numbers

Laminar horizontal buoyant jets have been found to exhibit peculiar behavior of unstable nature, e.g., bifurcation in the form of a vertical secondary plume deriving from the primary jet, due to the unstable stratification on one half of circumferential interface between the jet and the ambient fluid. However, whether and how this exceptional unstable jet behavior persists into the transitional regime with moderate Reynolds numbers (500<Re<2000) remains an open question. In this study, we explored the flow pattern and stability, i.e., the tendency to bifurcate, of horizontal buoyant jets with different densimetric Froude number (Fr) extending from low to moderate Reynolds numbers in the laboratory. The non-intrusive laser imaging technique of Planar Laser Induced Fluorescence (PLIF) was employed for the flow visualization and measurements. Three distinct flow patterns characterized with unstable small-scale structures, namely, ‘primary jet with vertical secondary plume’, ‘primary jet with pseudo secondary jet’ and ‘quasi-turbulent horizontal buoyant jet’, were identified in the Re–Fr parameter space determined from the visualization results. The substantive bifurcation reported earlier in the literature based on shadowgraph imaging was however not observed within the presumptive space in the present experiments. Quantitative concentration measurements using PLIF were further analyzed to study the jet mixing and spreading characteristics in the laminar and transitional regimes, including the decay of maximum concentration along the jet centerline, the cross-sectional concentration distribution at different downstream locations, as well as the concentration spread. Remarkably, the concentration decay/spreading rates exhibited a first-decreasing-then-increasing/first-increasing-then-decreasing behavior respectively with Re within the test range, reconciling the contradictory trends reported in the literature and suggesting the existence of a Re threshold below which the viscous force will prevail and suppress the potentially enhanced mixing and entrainment of low Re jet due to its less uniformity and coherence. Beyond the threshold, strong correlation of the concentration decay and spreading coefficients with Fr also confirmed that the jet mixing and spreading are dependent on the buoyancy-generated turbulence. Overall, the experimental results provided new insight on the flow patterns and mixing characteristics of horizontal buoyant jets in the laminar and transitional regimes.

Modeling sediment deposition from marine outfall jets

ABSTRACTThis paper presents a two-dimensional model to study the sediment deposition from marine outfall jets. The introduced unidirectional coupling (fluid–sediment) is an appropriate choice in the case of low-concentrated particle-laden jets such as municipal wastewater discharge, where the concentration of particles is small enough and does not affect the hydrodynamic development of the jet in the nearfield. The sedimentation model takes advantage of the preferential concentration phenomenon. The deposition criterion states that the deposition of sediments begins when the vertical component of the entrainment velocity becomes smaller than the settling velocity. Once the deposition process begins, it is controlled by the settling velocity, entrainment velocity, volume flux, and sediment concentration. The deposition along the jet trajectory is expressed by an ordinary differential equation coupled with the liquid phase equations. Experiments of Lane-Serff and Moran [Sedimentation from Buoyant jets. J Hyd Eng. 2005;131(3):166–174], Cuthbertson and Davies [Deposition from particle-laden, round, turbulent, horizontal, buoyant jets in stationary and coflowing receiving fluids. J Hydr Eng. 2008;134(4):390–402], and Lee [Mixing of horizontal sediment laden jets [dissertation]. Hong Kong: University of Hong Kong; 2010], chosen from bibliography, are used to validate the model. These experiments cover the cases of horizontal and inclined buoyant jets in stationary ambient, horizontal buoyant jets in co-flow current and nonbuoyant horizontal jets in stationary ambient. Good agreement between the experiments and the obtained simulations is revealed.

Large eddy simulation of turbulent horizontal buoyant jets

Large eddy simulations (LESs) of turbulent horizontal buoyant jets are carried out using a high-order numerical method and Sigma subgrid-scale (SGS) eddy-viscosity model, for a number of different Reynolds (Re) and Richardson (Ri) numbers. Simulations at previous experimental flow conditions (Re = 3200, 24, 000 and Ri = 0, 0.01) are carried out first, and the results are found to be qualitatively and quantitatively similar to the experimental results, thus validating the numerical methodology. The effect of varying Ri (values 2×10−4, 0.001, 0.005, and 0.01) and Re (3200 and 24, 000) is studied next. The presence of stable stratification on one side and unstable stratification on the other side of the jet centreline leads to an asymmetric development of horizontal buoyant jets. It is found that this asymmetry, the total radial spread and the vertical deflection are significantly affected by Ri, while Re affects only the radial asymmetry. The need for developing improved integral models, accounting for this asymmetry, is pointed out. Turbulent production and dissipation rates are investigated, and are found to be symmetric in the horizontal plane, but asymmetric in the mid-vertical plane. A previously proposed model, for correlation between the vertical component of the fluctuating scalar flux vector and the vertical cross-correlation component of the Reynolds tensor, is modified based on the current LES results. Instantaneous scalar and velocity fields are analysed to reveal the structure of horizontal buoyant jets. Similar to the developed turbulent jet, the flow close to the nozzle too is found to be markedly different in the stable and unstable stratification regions. Persistent coherent vortex rings are found in the stable stratification region, while intermittent breakdown of vortex rings into small-scale structures is observed in the unstable stratification region. Similarities and differences between the flow structures in the horizontal buoyant jet configuration and those in the jet in crossflow configuration are discussed. Finally, a dynamic mode decomposition analysis is carried out, which indicates that the flow in the unstable stratification region is more energetic and prone to instabilities, as compared to the flow in the stable stratification region.

An effect of a horizontal buoyant jet on the temperature distribution inside a hot water storage tank

The hot water storage tank (for stratified thermal storage) with a heat pump draws a lot of attention nowadays due to its high performance. In Japan, reheating of the bath is commonly used, and as this mode, the jet injects horizontally at the middle of the tank, so the temperature distribution of the tank changes complexly with time. Hence a model is needed to simulate this phenomenon, precisely. Additionally, in the process of designing a hot water storage system, it is necessary to simulate temperature distribution quickly, since a test run itself is a time consuming process.In this study, visualization experiments were performed using tracer particles and thermo-sensitive liquid crystals. Experiments were also carried out to find the unsteady temperature distribution in a tank when the positively or negatively buoyant jet was injected horizontally in the middle of the tank whose size is limited and has an influence from the opposite wall.If the momentum effect of the buoyant jet is stronger than that of buoyancy, the buoyant jet impinge against the opposite wall of the tank, and a vortex was observed near the opposite wall. Empirical formulas were proposed to predict the height of the vortex “Zb” under various conditions, such as the momentum and the buoyancy of the buoyant jet, and the Prandtl number of the tank water. Furthermore, the 3D-CFD was carried out to supplement the 3D behavior of the inner tank fluid.A one dimensional model, “uniformly distributed injection model”, for simulating temperature distribution was proposed. The performance of the model was verified by comparing the results with the unsteady temperature distribution obtained experimentally. The model was also compared with the measurements obtained using a commercially available hot water storage system. Both results showed good agreements. Hence adequacy of the model was clarified.

Viscous propagation of two-dimensional non-Newtonian gravity currents

This paper presents the results of a detailed experimental and theoretical investigation on the viscous propagation of non-Newtonian gravity currents. Laboratory gravity currents are generated in a horizontal rectangular tank by releasing a constant flux of high-concentration fluid mud suspensions that exhibit profound non-Newtonian (shear thinning) behavior. Experimental observations on the propagation of fluid mud gravity currents revealed that viscous propagation of these currents was typically preceded by two phases as expected: an initial momentum-driven horizontal buoyant wall jet and a buoyancy-driven inertial phase. The experimental transition times, t**, and positions, x**, at which fluid mud gravity currents transition into viscous propagation phase were determined. The experimental data that correspond to the viscous propagation of fluid mud gravity currents (i.e. experimental time, t ⩾ t**, and front position, xN ⩾ x**) were used to evaluate the predictive capabilities of two well-known mathematical modeling approaches: the lubrication theory approximation and the box-model approaches. Regarding the lubrication theory approximation, a recently developed self-similarity solution for viscous propagation of power-law gravity currents that has not been experimentally evaluated was used. Regarding the box-model approach, a viscous box-model solution for two-dimensional (2D) non-Newtonian gravity currents was developed. The evaluation of these models using experimental data revealed that both models were in good agreement with the experimental observations, despite several simplifying assumptions embedded in each. Given its more advanced mathematical development, the lubrication theory approximation model provides a more complete description of a gravity current (i.e. shape and velocity variation along the gravity current) than the box model at the expense of a relatively simple computational effort.

CFD 모델을 이용한 수중방류 온배수의 근역 동수역학 해석

온배수의 수중 방류 시 강한 방류 모멘텀 플럭스와 부력 플럭스에 의해 수중제트 인근에는 부력제트가 지배적인 근역이 형성되며, 이러한 근역을 해석하는 도구로써 비정수압 RANS 방정식을 적용한 전산유체역학(CFD) 모델을 이용하여 근역에 대한 적용성을 검토해 보았다. 과거 연구된 바 있는 원형 부력제트 수리실험과 유사한 조건으로 모델을 구성하고 정류시의 수평 부력 제트 경우와 가로흐름시 수직 부력 제트 경우에 대해 수치 실험을 수행하였다. CFD 수치실험의 결과는 수리실험 및 해석해 모델(CorJET)의 결과와 무차원화한 중심 궤적 및 희석율에 대해 비교 검증하였는데, 실제 수리실험의 결과와 잘 일치하는 것으로 나타났다. CFD 모델은 현재 근역 해석해 모델과 광역 준3차원 해수유동 모델이 가지고 있는 한계를 모두 보완할 수 있어 수중방류 온배수 영향해석에 적합한 모델이며, 본 연구를 통해 근역해석의 적합성을 확인하였으므로 향후 계산효율이 확보된다면 수중방류 온배수의 이동 및 확산 해석 도구로써 널리 활용될 것으로 기대된다. The buoyancy and initial momentum fluxes make near-field dominated by buoyant jet when thermal discharge releases underwater. In order to estimate prediction capabilities of those near-field phenomena, non-hydrostatic RANS applied CFD(Computational Fluid Dynamic) model was used. Condition of model was composed based on past laboratory experiments. Numerical simulations carried out for the horizontal buoyant jet in the stagnant flow and vertical buoyant jet into crossflow. The results of simulation are compared with the terms of trajectory and dilution rate of laboratory experiments and analytic model(CorJET) results. CFD model showed a good agreement with them. CFD model can be appropriate for assessment of submerged thermal discharge effect because CFD model can resolve the limitations of near-field analytic model and far-field quasi 3D hydrodynamic model. The accuracy and capability of the CFD model is reviewed in this study. If the computational efficiency get improved, CFD model can be widely applied for simulation of transport and diffusion of submerged thermal discharge.

Early development of the veil-shaped secondary flow in horizontal buoyant jets

Under specific conditions, a secondary flow can develop from a laminar horizontal buoyant jet released through a round nozzle. This secondary flow is a veil-shaped plane plume, which detaches from the main jet. The conditions for its apparition have been empirically determined and are available in the open literature. This paper aims to give theoretical basis to these conditions and to show some novel experimental observations and measurements on horizontal buoyant jets with secondary plume. One of the main results is the identification of the persistence of transversal velocity components in the release section of horizontal buoyant jets.

Non‐Boussinesq Integral Model for Horizontal Turbulent Buoyant Round Jets

Horizontal buoyant jet is a fundamental flow regime for hydrogen safety analysis in power industry. The purpose of this study is to develop a fast non‐Boussinesq engineering model the horizontal buoyant round jets. Verification of this integral model is established with available experimental data and comparisons over a large range of density variations with the CFD codes GASFLOW. The model has proved to be an efficient engineering tool for predicting horizontal strongly buoyant round jets.

Experimental investigation of wastewater discharges from a Rosette-type riser using PIV

The under-pressure-induced-ambient flow velocity and the bending phenomenon of the horizontal buoyant jets on a Rosette-type riser with four ports were observed by conducting the hydraulic experiments over a certain range considering the initial moment um and initial buoyancy. The measurement accuracy associated with the PIV system was verified. The velocity of the ambient flows into the inner side of the surrounding buoyant jets increased initially, and then decreased with the increase of the densimetric Froude number. The trajectories for low densimetric Froude numbers tended to rise up without strong bending whereas high densimetric Froude numbers resulted in more strongly bending trajectory and then led to the release of the bending trajectory with the increase of the densimetric Froude number. The low bending height resulted from the strongly bending buoyant jet. The experimental results revealed that the trajectories bend to the inner side with the increase of the ambient flow velocity.

정체수역으로 방류된 수평병합부력제트의 진동운동에 대한 실험적 연구

정체수역으로 방류된 수평병합부력제트의 진동운동에 대한 실험적 연구

Merging characteristics of buoyant discharges from Rosette-type diffusers in shallow water

The mixing characteristics of the Rosette-type diffuser consisting of four horizontal ports in each riser have been investigated by collecting extensive experimental data at a wide range of discharge and still water conditions in relatively shallow water. The merging height diagram, based on the numerical integration and iteration of few equations derived empirically and geometrically for merging in a riser and between risers, shows that the merging height increases with increasing riser spacing between risers. The experimental results for the surface minimum dilution at still ambient conditions show the underestimation of line plume soluti on to the measured values especially in shallow water and show the gradual decrease of surface minimum dilution at the merging of buoyant jets increases from the sequence of the dilution for a single horizontal buoyant jet, two-ports, and a four-port Rosette-type diffuser.

Numerical Simulation of Advected Thermal Using Gaussian-Vortex Model

The Gaussian-vortex integral model is applied to laboratory data on an advected thermal and field experimental data for a single submerged sewage outfall. The Gaussian-vortex integral model is distinguished from other conventional jet integral models that do not consider vortex-pair formation effects on the behavior of a buoyant jet in the buoyancy- and ambient-dominated regions. The experimental data relative to an advected thermal, measured by a laser-induced fluorescence technique were used for verifications of the numerical model. With the incorporation of vortex-pair formation effects, the simulated results on the bulk characteristics of an advected thermal were in good agreement with the laboratory data, and for applications the simulated surface minimum dilutions also show fairly good agreement with field experimental data. Finally, the numerical model is applied to a horizontal buoyant jet in cross-flow to demonstrate the capability of the numerical model for the buoyant jet that has 3D characteri...

Numerical Simulation of a Horizontal Buoyant Jet Discharged from a Multiple Pipe

The diffusion behavior of a horizontal buoyant jet discharged from a multiple pipe was investigated both experimentaly and numerically. Velocity and temperature of the jet were measured with FLV, thermocouples and propeller velocimeters, changing the number of pipe and the height of an outlet and the distance between the pipes. In each cases, a three-dimensional turbulence closure model (k-εmodel) was applied to simulate the behavior of the jets. The performance of the three-dimensional model was evaluated by the comparison of the numerical results with the experimental measurements.