Horizontal Jet Research Articles

The Study of Flame Length for the Horizontal Jet Flame of Carbon Dioxide and Propane Mixed Gas

Inert gases, such as carbon dioxide (CO₂), are often presented in fuel gases and influence their combustion characteristics significantly. This paper investigates the horizontal length of buoyant turbulent jet flame under different boundary conditions, including different nozzle diameters, heat release rates, and CO₂ volume fractions. According to the experiments, it is found that the horizontal length of jet flame increases with the heat release rate under the same nozzle diameter. Additionally, the flame length initially increases with CO₂ concentration but then decreases. Based on an analysis of the buoyancy and momentum flux of the turbulent jet flame, a new correlation has been developed, which relates the horizontal flame length to the heat release rate and CO₂ volume fraction. This correlation can be served as a valuable reference for fire prevention and control in gas leakage fire scenarios.

Thermal-induced buoyant water jet discharge under shallow coastal water conditions

A novel discharge dispersion model is developed to simulate the complex three-dimensional flow behaviour of thermal-induced buoyant water jets under current-wave coexisting conditions. The model solved the governing fluid flow and energy equations for two immiscible and incompressible phases (water and air) which were weakly coupled by applying the Boberbeck-Boussinesq approximation. Different turbulence models, such as k−ε multiphase, k-ω SST, k-ω SST-multiphase, k-ω SST-stable, and realizable k−ε were applied. Extensive verification of the model's performance is conducted by comparing the developed model results against a diverse range of analytical and experimental data. First, a series of simulations are carried out to evaluate the performance of the model in reproducing the results of the wave hydrodynamic and interactions with the submerged trapezoid bar. This is followed by numerically replicating the experimental results of a vertical non-buoyant submerged jet under current-only and current-wave environments. Finally, the potency of the coupled hydro-thermal algorithm is assessed by validating against different thermal-induced buoyant submerged jet experimental tests. For this purpose, numerical prediction of the developed model is tested against physical experiments for a series of tests for thermal-induced buoyant submerged horizontal jets in stationary water and inclined thermal-induced buoyant water jet under the influence of current-wave environments. Results showed that the k-ω SST-multiphase provides the best agreement with the laboratory measured data in terms of flow, temperature distribution field, plume trajectory and dilution. The findings confirmed that the developed model can be used as a reliable tool in precisely modelling characteristic of thermal-induced buoyant water jet in shallow coastal waters.

Trajectory and spreading of falling circular dense jets in shallow stagnant ambient water

This study investigates the trajectory and spreading of a horizontal circular dense jet flow discharged above the water surface, the flow of which falls into shallow stagnant ambient water. For this purpose, 27 experiments were performed using three diameters, flow rates, and falling heights to investigate jet trajectory. In addition, nine experiments with constant falling height were conducted to study jet spreading. The densimetric Froude number of the jet flow at the nozzle outlet and water surface of the present study ranged from 0.72 to 4.22 and 36.96 to 86.10, respectively. The data pertaining to this study were extracted and analyzed through image processing. The results of the experiments showed that by increasing both the momentum and falling height, the trajectory of the jet flow reached a farther distance from the discharge nozzle. The spreading of the outer boundaries of the dense circular falling jet flow tended to extend downstream of the impact point and had an elliptical motion on the bed. The relationship between radial distance from the impingement point to the outer boundary of flow and time was determined to have a power of 0.67 for flow along the flume and 0.59 for flow along the flume's width.

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.

Large eddy simulation of round jets with mild temperature difference

Understanding the behaviour of hot jets is crucial for various engineering and environmental applications. The present work studies the influence of heat transfer on the dynamics of horizontal round hot jets through Large Eddy Simulations (LES). Our focus lies on trajectory development, large-scale coherent structures, and turbulent kinetic budget analysis in the near-field and intermediate-field regions. LES of two horizontal round hot jets with Reynolds numbers (3934 and 5100) and corresponding Froude numbers (32.98 and 17.07) were carried out using buoyantPimpleFoam solver in OpenFOAM, and the simulation on an isothermal jet was also performed as a baseline for comparison. The results reveal that the jet core temperature decays faster in the streamwise direction but more slowly in the radial direction, indicating a wider temperature spread than velocity, and the maximum difference between the temperature and velocity spread is about 0.5D. Moreover, the energy associated with the large-scale coherent structure decreases with increasing initial jet temperature. The energy of the first two modes of snapshot Proper Orthogonal Decomposition (POD) and extended POD dropped by 12% and 14%, respectively. The coherent motion with the greatest correlation between the temperature and velocity fluctuations is identified as four pairs of Q1 and Q3 events, which are Reynolds shear stress dominant events. Furthermore, compared with the isothermal jet, the turbulent kinetic energy budgets of the hot jets indicate that the diffusion and generation terms are both reduced by approximately 50%, suggesting a transfer of more kinetic energy into potential energy rather than turbulence. The finding highlights the potential of heightened temperatures to mitigate instabilities associated with large-scale motions in hot jets. This study fills the gap on a comprehensive analysis of heat transfer effects on jet dynamics, and quantitative insights into the large-scale coherent structures are provided, contributing to a better understanding of hot jet behaviour.

Experimental study on the flame trajectory evolution of horizontal jet fires under reduced pressures

Jet fire including process pipeline/tank leakage, oil exploitation industry of tail gas treatment flare or other industrial combustors as a common phenomenon can be found at high altitude areas. This work characterizes the flame trajectory evolution of horizontal jet fires under reduced pressures, which is rarely studied. The experimental results show that the horizontal flame projection distance increases monotonously, but the vertical flame length first increases and afterward decreases with the increase of heat release rate and the decrease of ambient pressure. Meanwhile, flame trajectory length increases significantly and then slowly with increasing heat release rate, but first increases to a maximum value and afterward declines with decreasing ambient pressure. Meanwhile, the turning point of vertical flame length appears earlier than that of flame trajectory length with increasing heat release rate (or jet velocity at source) and decreasing ambient pressure. Then, a mathematical model based on the flame arc hypothesis and a dimensionless model were proposed to describe the flame trajectory length, the momentum-buoyancy length scale Lm=(M0/g′)1/3 was used to normalize the flame trajectory length. The measured flame trajectory length in terms of the nozzle diameter, heat release rate, and ambient pressure was satisfactorily correlated by the proposed models.

Water Injection for Cloud Cavitation Suppression: Analysis of the Effects of Injection Parameters

This study investigates cloud cavitation suppression around a model-scale NACA66 hydrofoil using active water injection and explores the effect of multiple injection parameters. Numerical simulations and a mixed-level orthogonal test method are employed to systematically analyze the impact of jet angle αjet, jet location Ljet, and jet velocity Ujet on cavitation suppression efficiency and hydrofoil energy performance. The study reveals that jet location has the greatest influence on cavitation suppression, while jet angle has the greatest influence on hydrofoil energy performance. The optimal parameter combination (Ljet = 0.30C, αjet = +60 degrees, Ujet = 3.25 m/s) effectively balances energy performance and cavitation suppression, reducing cavitation volume by 49.34% and improving lift–drag ratio by 8.55%. The study found that the jet’s introduction not only enhances vapor condensation and reduces the intensity of the vapor–liquid exchange process but also disrupts the internal structure of cavitation clouds and elevates pressure on the hydrofoil suction surface, thereby effectively suppressing cavitation. Further analysis shows that positive-going horizontal jet components enhance the lift–drag ratio, while negative-going components have a detrimental effect. Jet arrangements near the trailing edge negatively impact both cavitation suppression and energy performance. These findings provide a valuable reference for selecting optimal injection parameters to achieve a balance between cavitation suppression and energy performance in hydrodynamic systems.

The influence of air distribution ratio on the fluctuation characteristics and stability of horizontal jet diesel non-premixed flame under extreme sub-atmospheric pressures

The burning problem in the plateau environment attracts more and more people’s attention, and the plateau adaptability and flame stability of burner are the focus of recent research. The main purpose of this paper is to reveal the horizontal jet spray flame fluctuation characteristics and stability change rule under extremely low pressure (0.05 MPa) at a high altitude (about 5500 m) inhabited by human beings. Flame morphology and temperature properties were investigated in a low-pressure chamber with different secondary air ratios (23–53 %). It is found that the normalization of the flame trajectory equation is not affected by the ratio of secondary air. The temperature in the flame recirculation zone can be increased by 110 K as the proportion of secondary air increases to 45 %, but the maximum temperature is still lower than 1500 K. A continuous flame image processing method was implemented to define and analyze the flame fluctuation region. The results show that the dimensionless fluctuation parameter γ can predict the flame stability in advance than β. When the secondary air ratio is 40 %, the flame has the largest upward fluctuation; and when it exceeds 45 %, the flame stability becomes worse. This work is the first to obtain the results of the study on flame morphology and stability of horizontal jet spray flame distribution ratio under extremely low atmospheric pressure, which provides a theoretical scientific basis for the design of plateau burner, flame control, and flame stability improvement.

Pre-Support Method for Horizontal Overlapping Jet Grouting Columns for Very-Large Cross-Section Tunnels in Dry Silty Sand Strata: A Case Study

The Shangbai Tunnel on the Daxi Passenger Dedicated Line passes through unsaturated dry silty sand strata which is prone to sand leakage and gushing after disturbance, posing a significant threat to the safety and progress of construction work. Using the Shangbai Tunnel project as a case study, we conduct laboratory experiments to determine the physical and mechanical properties of dry silty sand layers and analyze the limitations of advanced large pipe shed pre-support and small pipe grouting pre-support structures. The objective is to evaluate the feasibility and reveal the mechanism of horizontal rotary jet grouting for column formation and pre-support. The physical and mechanical properties of the consolidated body of the overlapping columns are evaluated. Three pre-reinforcement schemes using overlapping columns for tunnels crossing different subsurface profiles are proposed. Experiments are conducted to assess the physical and mechanical properties of the overlapping columns, and on-site monitoring and analysis of the tunnel arch settlement and stress changes are performed. The results indicate that the proposed method for creating overlapping columns ensures the stability of the working face, controls arch settlement, and is cost-effective. Our study summarizes the findings from the data and information for the construction of similar projects.

TempFlow Insight: AI-Powered Thermal Analysis of Horizontal Jet Cooling System on Vertical Target

This paper delves into the TempFlow Insight project, which employs advanced artificial intelligence (AI) algorithms to analyze temperature distribution in a horizontal jet cooling system on a vertical target. The integration of AI algorithms represents a significant advancement in thermal analysis, aiming to optimize cooling mechanisms and enhance energy efficiency.

Stagnation point heat transfer under a free-surface jet

Laminar free-surface jet impingement is a crucial configuration for heat transfer processes. Focusing on the link between stagnation-point heat transfer and near-axis radial acceleration, its dependence on jet width and profile is studied. Thus, heat transfer depends on: fluid properties, flow rate, nozzle length, nozzle-to-plate spacing, surface tension and gravity (Pr, Re, L/d, H/d, We & Fr, accordingly). As existing theory is limited to specific cases, a new general description is developed from analogy to submerged jets. Validated by two-phase flow simulations, this description captures key jet dynamics evolution (centerline velocity, profile curvature). It reveals significant property changes during jet flight due to relaxation (L dependence) and contraction (Re/Fr dependence). Unlike submerged jets, contraction raises arrival Reynolds number, leading to additional dependencies Nu ∝ L and Nu ∝ H/Fr, and further deviations at low-We and -Re. The theory successfully predicts heat transfer across diverse conditions and converges to negligible gravity (horizontal jet) as expected.

Visual observations of steam–air submerged horizontal jets at low mass flux

Steam jet condensation at low mass flux is important especially in start-up, shutdown or accident conditions of various applications. Visual experiments of steam–air submerged jets through horizontal pipe were conducted in the ranges of mass flux 0–––20 kg/m2s, air mass fraction 0–––0.02, and water temperature 20 − 80℃. In pure steam jets, three condensation regimes of no bubbling, intermittent bubbling, and continuous bubbling were identified in steam jets. In no bubbling regime, rolling up and billows of plane shear flow were observed. In intermittent bubbling regime, large bubble was generated, detached and collapsed intermittently, accompanied by fluid oscillations. The bubble forming frequency increased with the rise of water temperature. Condensation heat transfer coefficients tends to decrease as the steam mass flux increases. In continuous bubbling, fluid oscillation no longer occurred. The bubble forming frequency decreased with the rise of water temperature. Condensation heat transfer coefficients increase as the steam mass flux increases. In the cases with shallow submerged depth, air-entrained vortex, surface water jets, and splash were observed after bubble condensation. In steam–air jets, condensation became stable and small bubbles increased. The condensation regime transitioned from intermittent bubbling to continuous bubbling earlier.

Tracking the Nearfield Evolution of an Initially Shallow, Neutrally Buoyant Plane Jet Over a Sloping Bottom Boundary

AbstractUnderstanding coastal plane jets which occur when a body of water discharges into an ocean or a lake through a channel or outlet is important, since they play a significant role in sediment, nutrient, and pollutant exchange. This study investigates the nearfield of initially shallow, neutrally buoyant plane jets, bounded by a free surface and a sloping bottom (Sloping Bottom Jet; SBJ) that issue into a laterally unconfined quiescent ambient both experimentally and numerically, and compares them with a plane jet flowing over a horizontal bottom (Horizontal Bottom Jet; HBJ). Results revealed that, different from the HBJ, the width and centerline velocity of SBJ decrease near the mouth. The SBJ width gradually increases after that as the transverse longitudinal velocity profile progressively transforms from a “top‐hat” into a Gaussian distribution. Once the Gaussian distribution is established, both jets diverge and centerline velocity decreases. Shear layers are generated on the sides of both jets with Kelvin Helmholtz‐type Coherent Structures (KHCS) developing inside. KHCS produce periodic velocity fluctuations with a Strouhal number of ∼0.079 and contribute significantly to momentum exchange and turbulent kinetic energy production. Since the thickness of the SBJ increases longitudinally, the vertical extent of KHCS also increases. When the two shear layers meet and merge at the centerline, they cause a flapping motion of the jet. This location is closer to the jet mouth for SBJs than for the HBJ. These findings demonstrate that a sloping bottom modifies the flow field from quasi‐2D for the HBJ to strongly 3D for SBJs.

Numerical investigation of force over the horizontal jet tab of various sector angle fixed to the convergent-divergent nozzle exit

Abstract In this study, a CFD computational model has been established to properly simulate complex correctly expanded supersonic flow generated by a three-dimensional C–D nozzle for the purpose of Thrust Vector Control (TVC) simulations. Jet tabs affixed to the perimeter of the nozzle exit are used to achieve thrust vectoring. This study focuses on the estimation of the force on the tabs due to the jet issued from the C–D nozzle using Ansys 19.2 three-dimensional density based solver, implicit formulation with SST K–ω turbulence model. The force is calculated for different tab configurations based on tab sector angles of 60°, 90°& 120° for the designed Mach number and X/D ratio of 0.7. The nozzles with Mach 1.6, Mach 1.8 and Mach 2.0 designed using SolidWorks are compared. It has been observed that with an increase in sector angle, tab force increased by an average of 70 % for sector angle of 60° to 90° and 36 % for sector angle of 90° to 120°.

Experimental study of turbulent flow in lower plenum with flow skirt of reactor pressure vessel of pressurized water reactor

The turbulent flow in lower plenum of reactor pressure vessel (RPV) of pressurized water reactor (PWR) is an important phenomenon for design of flow mixing device. A high-precision matched index of refraction (MIR) technique is requisite for time-resolved particle image velocimetry (TR-PIV) measurements in RPV with complicated internals. In this study, turbulent flow in a scaled-down RPV model was measured by TR-PIV under different Reynolds numbers (Re) and asymmetrical flow rate with aid of the high-precision MIR technique of sodium iodide (NaI) solution and acrylic. The time-averaged flow structures include flow separation at the corner of lower support plate, fluid bifurcation around the lower edge of flow skirt, flow turning upward below the vortex suppression plate, horizontal jets at holes of flow skirt, vertical jets at holes of vortex suppression plate, improving turbulent mixing and Reynolds stresses in the lower plenum. The coherent structures were studied by proper orthogonal decomposition (POD) analysis. The flow skirt and vortex suppression plate break down large vortices through them. With Re increasing, Reynolds stresses decrease fast, and the energy fractions of low-order modes transfer into high-order modes, because turbulent vortices break up. In the case of asymmetrical flow rate, the time-averaged velocity and Reynolds stress decrease slightly, and the cumulative energy fraction decreases at flow skirt and vortex suppression plate.

Numerical investigation of the underwater explosion of a cylindrical explosive with the Eulerian finite-element method

The shock wave and bubble dynamics of an underwater explosion are significant in various fields. When the charge is non-spherical, the detonation process will remarkably affect the shock wave formation and the subsequent bubble motion. In this work, the underwater explosion of a cylindrical explosive is investigated numerically with the Eulerian finite-element method combined with the programed burn model treating the detonation process. The present model is validated by comparing the simulated results with the experimental ones. Then, several cases with different slenderness of the explosive charge in various buoyancy environments are simulated and analyzed. The results demonstrate a notable variation of the shock wave in different directions. The shock wave will reach the highest pressure peak and shortest pulse width at a certain angle determined by the ratio between the speeds of the detonation wave and the shock wave. Furthermore, the non-spherical initial expansion of the bubble casts a significant influence on the subsequent bubble evolution. Three typical jet morphologies are identified with different combinations of buoyancy parameter and oblateness ratios of the bubble, featured by a slightly oblique upward jet penetrating the bubble, a laminar jet that failed to penetrate the bubble continuously, and a pair of opposite horizontal jets penetrating the bubble. Meanwhile, the horizontal jets that happen under a weak buoyancy environment will reduce the upward migration.

Experimental study on flame geometric of horizontal jet fire inpinging a facing wall and side wall

This work focuses on investigating the characteristics of restricted horizontal jet fire caused by fuel leakage as a pipeline or tank fracture. The study aims to quantify the effect of the exit velocity and nozzle-facing wall distance on the flame height and width, as well as developing a new non-dimensional heat release rate, Q*n , to better characterize the flame geometry. The study conducted three nozzle-facing wall distances (0.05 m, 0.10 m, and 0.15 m) with varying fuel ejection speeds from 1.04 m/s to 6.25 m/s. Results show that the flame height and width increase with both the nozzle-facing wall distance and fuel ejection speed. The sidewall constrains the air entering into the fire plume, which pushes the flame closer to the sidewall. A new non-dimensional heat release rate, Q*n , was proposed on the basis of plate-nozzle distance, that the flame height and width fit well with the 1/4 and 2/5 power of Q*n , respectively. The global model was developed for flame size under multiple restrictions. The findings of this study are crucial in improving our understanding of the restricted horizontal jet fire accidents caused by fuel leakage and can aid in developing measures to minimize potential casualties and economic losses.

Experimental investigation of flow characteristics of a jet in low atmospheric pressure conditions on the Tibetan Plateau

The indoor humidity of heated buildings on the Tibetan Plateau can be as low as 5%RH. Indoor air humidification is very important to people's life and health. Due to the low atmospheric pressure on the plateau, the air physical parameters and wet component diffusion characteristics are different from those of standard atmospheric pressure. This paper investigates experimentally the effects of horizontal and vertical wet jets with various initial velocities, pipe diameters, ambient temperatures, and moisture temperatures on the indoor temperature and humidity field. It is shown that low atmospheric pressure will lead to an increase in relative humidity nearly the jet outlet, but the effective moisture delivery distance becomes shorter and the actual moisture load increases. When the same relative humidity is reached, the specific humidity under low atmospheric pressure is about 1.5–2.5 times as that under standard atmospheric pressure. The average relative humidity of jets produced by the ultrasonic humidification source is 10% higher than the evaporative humidification source during the same time. During the actual humidification process, it is necessary to consider the balance between the initial velocity of the jet and the humidification distance and select the jet tube diameter according to the humidification space area. Additionally, choosing a jet with a temperature slightly higher than the ambient temperature can avoid reducing the indoor temperature. This study should be helpful to the plateau humidification jet characteristics and parameter selection.

Application of Artificial Neural Networks for Mathematical Modelling of Horizontal Jet Fires

Aim: This article focuses on the use of artificial neural networks to mathematically describe the parameters that determine the size of a jet fire flame. To teach the neural network, the results of a horizontal propane jet fire, carried out experimentally and using CFD mathematical modelling, were used. Project and methods: The main part of the work consisted of developing an artificial neural network to describe the flame length and propane-air mixing path lengths with good accuracy, depending on the relevant process parameters. Two types of data series were used to meet the stated objective. The first series of data came from field tests carried out by CNBOP-PIB and from research contained in scientific articles. The second type of data was provided by numerical calculations made by the authors. The methods of computational fluid mechanics were used to develop the numerical simulations. The ANSYS Fluent package was used for this purpose. Matlab 2022a was used to develop the artificial neural network and to verify it. Results: Using the nftool function included in Matlab 2022a, an artificial neural network was developed to determine the flame length Lflame and the length of the Slift-off mixing path as a function of the diameter of the dnozzle and the mass flux of gas leaving the nozzle. Using Pearson’s correlation coefficient, a selection was made of the best number of neurons in the hidden layer to describe the process parameters. The neural network developed allows Lflame and Slift-off values to be calculated with good accuracy. Conclusions: Artificial neural networks allow a function to be developed to describe the parameters that determine flame sizes in relation to process parameters. For this purpose, the results of the CFD simulations and the results of the jet fire experiments were combined to create a single neural network. The result is a ready-made function that can be used in programmes for the rapid determination of flame sizes. Such a function can support the process of creating scenarios in the event of an emergency. A correctly developed neural network provides opportunities for the mathematical description of jet fires wherever experimental measurements are not possible. Solution proposed by the authors does not require a large investment in ongoing calculations, as the network can be implemented in any programming language. Keywords: computational fluid mechanics, artificial neural networks, jet fire

NUMERICAL INVESTIGATION OF TURBULENCE CHARACTERISTICS AND SELF-SIMILARITY IN A HIGHLY AERATED STABLE HYDRAULIC JUMP USING LARGE EDDY SIMULATION

This work presents a numerical study of a stable hydraulic jump at Froude number 4.25 and Reynolds number 1.15×105 inside a horizontal and rectangular channel with a length of 3.2 m, a width of 0.5 m and a height of 0.4 m using large eddy simulation (LES). Classical hydraulic jump characteristics are obtained, such as conjugate depths, jump length, void fraction and velocity profiles. The hydraulic jump maximum streamwise velocity decay and shear layer spreading rate are simulated and compared with experimental data. For these parameters, numerical results demonstrate that is possible to stablish an analogy with other shear flows, such as the horizontal plane wall jet. Profiles of streamwise and vertical components of mean velocity are simulated, and self-similarity is observed for cross-sections located at the recirculation region of the jump. Self-similarity is also observed in terms of turbulent fluctuations, insofar as LES simulations indicate a high level of turbulence in the recirculation region. The simulated root mean square of streamwise velocity fluctuations, , ranges from 0.5 to 0.7 of the maximum cross-sections velocity, whereas the root mean square of vertical component of velocity fluctuations, , stays around 0.5 of the maximum cross-sections velocitiy. All validation comparisons show good agreement with the selected experimental data of Kramer and Valero (2020) and Wang (2014), presenting average deviations always lesser than 5%.