Behavior Of Jet Research Articles

Quantitative evaluation on the cavitation damage energy of metals via multiscale approaches

In-situ experimental observation cannot be an effective method in the impact process of metal cavitation erosion, and the impact damage energy prediction theory has not been established based on a detailed mathematical and physical model. Research has shown that the metal material can be regarded as a sensor to reflect the impact parameters. Soft metal materials such as industrial pure copper with a single α-phase microstructure can be a suitable sensor to detect cavitation erosion effects, revealing the impact behaviors of the cavitation jet through the depth, width and spatial distribution of cavitation pits on the surface. In this scenario, volume loss of cavitation pits on a macro/mesoscale are obtained by three-dimensional surface measurement. A coupled fluid-solid simulation model calculating the impact damage energy on a macro/mesoscale is established based on the Smoothed Particle Hydrodynamics (SPH) and the Crystal Plasticity Finite Element Method (CPFEM). Python programming is used to set the trajectory of SPH particles to determine the macro cavitation flow field. IFEM methods were used to construct the prediction theory of cavitation impact energy in a relatively simple exponential equation, establishing the quantitative relationship between cavitation impact damage energy and measured volume of cavitation pits. Compared with conventional measurement and simulation, the present multiscale approaches are assumed as a further step advancement towards calculating the impact damage energy of cavitation water jet.

Analyze the influence of nozzle shape and orientation on inline arrangement of multiple jets impingement on a concave surface

ABSTRACT The present study reports the thermal behavior of multiple jets on a hot concave surface with different nozzle geometries such as circular and elliptical and different orientation. Tests are performed with five different nozzles at different values of nondimensional nozzle to surface distance (z/d = 2–10) and Reynolds number (5000–28,000). Here, the parameter coefficient of variation (COV) is used to estimate the non-uniformity in the local Nu variation. For N-2, the value of CO V y , non − dim is found to be 50–60% higher compared to N-3 at z/d = 2; while at z/d ≥ 8, for N-3, the value of CO V y , non − dim is found to be 10–15% higher compared to N-2. The higher temperature uniformity ( CO V x , non − dim ) is noted in the fountain region compared to impingement region for the circular and elliptical nozzles. The thermal performance of elliptical jets is found to be sensitive toward the jet orientation at lower z/d values. The magnitude of temperature non-uniformity decreases with the increase in the z/d values. Among the tested nozzles, Nozzle N-2 consistently demonstrates superior performance across all nozzle-to-plate distances and with an increase in the z/d value improvement with nozzle N-2 reduces.

Active flow control on unsteady cloud cavitation: Insights into jet dynamics

Unsteady cloud cavitation significantly impairs the performance of marine systems. Active flow control method has shown promise in effectively reducing cavitation, yet its specific mechanisms of action require elucidation. This study investigates continuous water injection on a NACA66 (MOD) hydrofoil as an active control against unsteady cloud cavitation. Results show notable reductions in cavitation volume: 52.57 % at a cavitation number of 0.83 and 86.24 % at 1.29. Employing the Lagrangian approach, the study tracks ideal particles to explore the jet's behavior and its interaction with cavitation. The interaction between the jet and cavitation is reciprocal: cavitation draws the jet, which in turn alters the cavitation's structure. The jet's movement is synchronized with the evolution process of cavitating flow, effectively limiting the spread of attached cavitation, disrupting cloud integrity, and encircling scattered clouds to prevent their growth. The analysis identifies the jet's streamwise direction as critical in suppressing cavitation, with the normal direction providing supplementary support, and the spanwise direction having minimal impact. Furthermore, the jet promotes a condensation-dominant state in local flow regions, hindering cavitation growth by altering the water-vapor mass transport process.

Evaluation of the jet distortion by sediment erosion in the needle in the Pelton turbines

Abstract In order to succeed in the transition to a more renewable energy sector, the hydropower industry must overcome multiple challenges in the coming decades, including the need for faster and reversible turbines to support emerging renewable energy sources. In addition, the location of new projects in tropical and semi-tropical areas poses unique considerations, as does the increase in sediment. Evaluating sediment erosion in turbines is a critical challenge, which may partly be addressed by analyzing the behavior of water jets from eroded nozzles in Pelton turbines. This paper presents an evaluation of the quality of the jet under various hydraulic conditions, focusing on needle erosion. The study is part of a research project conducted in the Waterpower Laboratory at NTNU, focusing on Pelton turbines. Furthermore, this paper investigates erosion patterns caused by sediments on the needle and explores the impact on jet performance. Through high-speed visualization and image processing, the behavior of a jet from the needle tip to a representative distance downstream has been investigated. The investigation revealed discernible differences between jets with eroded and uneroded needles in size and edge variation.

Behavior of a stationary jet of concentrated polyacrylonitrile solution

Behavior of a stationary jet of concentrated polyacrylonitrile solution

Flowfield and Noise Dynamics of Supersonic Rectangular Impinging Jets: Major versus Minor Axis Orientations

The current study explores the flowfield and noise characteristics of an ideally expanded supersonic (Mach 1.44) rectangular jet impinging on a flat surface. The existing literature is primarily concentrated on axisymmetric jets, known for their resonance dominance, pronounced unsteadiness, and acoustic signatures. In contrast, non-axisymmetric jets remain relatively less understood, particularly those impinging on a ground surface. By employing Schlieren imaging, high-frequency pressure measurements using high-bandwidth transducers, and particle image velocimetry (PIV), this research comprehensively examines the flow-acoustic phenomena. Schlieren imaging revealed distinct, coherent structures and strong acoustic waves, while pressure measurements at the impingement surface exhibited high-amplitude fluctuations, peaking at approximately 186 dB. Acoustic analysis identified multiple high-amplitude tones with unique directional characteristics, suggesting the potential for multiple simultaneous modes in rectangular jets. Furthermore, the PIV data elucidated differences in the jet shear layer and wall jet development attributed to the nozzle orientation. These findings contribute to a deeper understanding of non-axisymmetric jet behavior, offering insights relevant to fundamental flow physics and practical applications such as vertical takeoff and landing aircraft.

Combustion Behavior of Supersonic Jet for Single‐Flow Postcombustion Oxygen Lance with Various Secondary Nozzle Parameters

A 3D model is established to discuss the influence of combustion reaction on jet characteristics. Based on this, combustion behaviors of supersonic jet for single‐flow postcombustion oxygen lance with various secondary nozzle parameters (diameter, inclination angle, and number) are analyzed. The results indicate that after activating combustion reaction, the jet velocity, dynamic pressure, density, and temperature of primary jet at H = 1.45 m are 1.27, 1.15, 0.56, and 1.97 times than those of without considering the combustion, respectively. Enlarging secondary nozzle diameter is helpful to extend the flame core lengths of primary and secondary jets (the axial distance from lance tip to isotherm of 1773 K) as well as the combustion region. With the increase of secondary nozzle angle, the two flame core lengths both decrease, while the combustion zone increases. Increasing the number of secondary nozzles, the flame core length of primary jet increases while that of the secondary jet decreases, and the combustion region first increases and then decreases. As for the influences of the above parameters on flame core lengths of primary and secondary jets as well as the combustion region, the number is the greatest, followed by the inner diameter, and the inclination angle is the smallest.

Experimental investigation on the development characteristics of high-pressure hydrogen jet flame under different ignition conditions

With the rapid development and application of hydrogen in the chemical and energy industry, the safety of hydrogen industrial facilities has been widely concerned. In this study, the safety of hydrogen accidently released from a high-pressure tube storage system (tube diameter:10 mm, storage tank volume:4 L) was explored experimentally. The combustion behavior of the transient hydrogen jet and explosion overpressure under self-ignition and electric spark induction were investigated. Besides, the explosion overpressure and jet flame evolution laws of the hydrogen cloud induced by the release of unsteady turbulent hydrogen jets into the open environment were analyzed. The results revealed that the peak value of hydrogen self-ignition explosion overpressure was higher than that of electric spark ignition overpressure. Compared with spark ignition, hydrogen self-ignition flame structures can be maintained for longer time. However, spark ignition at low release pressures was more likely to cause hydrogen ignition and explosion compared to self-ignition. Finally, the combustion behavior and potential hazards of the ignited free transient hydrogen jet under different ignition modes were analyzed. This study can provide a reference for the prevention and control of hydrogen explosion accidents in practice.

Numerical simulation of dynamics behavior of pulsed-DC helium plasma jet confined by parallel magnetic field at atmospheric pressure

A two-dimensional axisymmetric fluid model is used to simulate the dynamics behavior of an atmospheric-pressure helium plasma jet in the presence of a parallel magnetic field. The plasma jet is generated in a coaxial dielectric barrier discharge (DBD) driven by pulsed direct-current voltage. Comparative analysis of the plasma jet with and without the parallel magnetic field indicates that a slightly thinner plasma sheath inside the tube is present with the parallel magnetic field as a result of the decreased accumulated electrons on the inner surface of dielectric tube. After the streamer propagates outside the tube, a little more concentrated electron distribution in the annular wall is observed by applying the magnetic field because of the reduced electron diffusion in the radial direction and the confinement effect of the magnetic field on the electrons in the avalanche heads. The tiny reduction in the length of plasma jet is attributed to the E × B drift of charged particles. These results demonstrate that the parallel magnetic field has no apparent effect on the propagation of the plasma jet, and it contributes little to the performance improvement of the coaxial DBD, which agrees well with the previous experimental observations. This little impact of the parallel magnetic field on the coaxial DBD plasma jet may result from negligible contribution of the memory effect to the sole discharge pulse as well as the weak confinement effect of the applied magnetic field on the surface electrons that moves along the magnetic field lines under electrostatic repulsion. Published by the American Physical Society 2024

Effects Of The Nozzle Exit Section Shape On The Velocity Field And Heat Transfer Of Impinging Synthetic Jets

"The versatility and effectiveness of synthetic impinging jets for cooling applications have pushed the scientific community to optimize the design of such devices investigating the effects of all the relevant flow parameters, such as the stroke length, the Reynolds number and the shape of the driving wave. The current work focuses on the influence of different nozzle exit section shapes on the flow field evolution and heat transfer behavior of synthetic jet. In work presented herein, the actuator consists of a loudspeaker oscillating inside a cavity provided with a nozzle that has a circular entry section and a variable-shape exit section with a fixed hydraulic diameter (equal to 20 mm). The exit section shapes investigated in the current work are the circular, the triangular, the square and rectangular one with aspect ratio equal to 2. Simultaneous synchronized two component particle image velocimetry and infrared thermography measurements are performed. Consistent results are found both in terms of flow fields as well as Nusselt patterns: small nozzle-to-plate distances exhibit less spreading of the jet combined with a less spreaded, although more intense, Nu pattern. Smaller nozzle-to-plate distances also reveal the shape of the nozzle in the thermal pattern: this behavior can be seen for every nozzle, and it is associated with the presence of a Nu peak in correspondence of every corner of the shape, where the three-lobe footprint of the triangular nozzle exit section shape is clearly visible. Larger nozzle-to-plate distances are associated with a higher spreading in the jet and a lower vertical velocity in the vicinity of the impinged plate. "

Flow dynamics and mixing of jet in crossflow with cylindrical cavity

The flow dynamics and mixing characteristics of an air jet issued from a cylindrical cavity in an air crossflow are numerically studied using a large-eddy-simulation technique. The cavity, aligned concentrically with the jet, is located beneath the crossflow wall. The jet-to-crossflow velocity ratio is 4, and the Reynolds number for the jet flow is 1.39×104 based on its diameter and centerline velocity. The presence of the cavity significantly influences the early evolution of the jet and its interaction with the crossflow. Complex vortical structures are observed. Notably, windward vortices on the jet surface increase in size, accompanied by a reduction in the Strouhal number. For a deep cavity, these vortices break down and result in small vortical tubes in the jet streamwise direction due to secondary instability. Also examined are leeward shear-layer vortices, hanging vortices, wake vortices, and the recirculating flow within the cavity. Their roles in the mixing between the jet fluid and the crossflow are identified. The cavity enhances mixing. The effect is significant in the near field but diminishes in the far field. By adjusting the cavity radius and depth, it is determined that the cavity depth exercises a more profound impact on jet evolution and mixing than the cavity radius. The most substantial influence occurs when a narrow and deep cavity is implemented. These findings may serve as guidelines for optimizing cavity design for effective modulation of jet behaviors.

Effect of impinging jet on rapid cooling of a miniature Joule-Thomson cryocooler: Experimental study of operating conditions

A miniature open-cycle Joule-Thomson (J-T) cryocooler possesses excellent potential for rapid cooling from ambient temperature to about 100 K within seconds. In this rapid cooling process, the interplay of the heat transfer process between the cryogenic fluid and the cold plate plays a crucial role, in addition to the J-T effect and the energy recovery within the heat exchanger of the cryocooler. The phase state of the impinging jet is determined by the jet temperature and has different heat transfer mechanism. To investigate this impinging jet behavior separately, an experimental system for the rapid cooling J-T cryocooler was set up and the jet temperature was measured besides other important parameters. The operating conditions, including the cylinder pressure, cylinder volume, ambient temperature, and the refrigerant, were studied orthogonal. It was observed that argon, compared to nitrogen, can be more rapidly throttled into its two-phase region within a second. However, nitrogen will perform better than argon in terms of cool-down time. This is attributed to the temperature difference between the jet and the cold plate, which significantly influences the boiling mode of the two-phase jet, and in turn affects the cryocooler's cooling rate. Nevertheless, due to the smaller heat transfer intensity of single-phase jet, the cool-down time of nitrogen deteriorates quickly at high ambient temperatures. Experimental results also revealed that the cooling rate of the cryocooler still can be enhanced even if cylinder pressure beyond its saturation curve, caused by the dynamic cooling process and the pressure drop within the finned tube.

Viscous fluid flow and heat transfer past a permeable wall jet with convective boundary conditions

PurposeThe steady laminar wall jet flow over a stretching/shrinking surface in the presence of lateral suction or injection with a convective boundary condition is considered.Design/methodology/approachThe partial differential equations for mass, momentum and energy conservation are changed to the system of ordinary differential equations through similarity solution transformations. Solutions, both numerical and asymptotic, to these similarity equations are found in some new ranges of parameters in the governing equations.FindingsThe equations are solved both asymptotically and numerically for a range of the transpiration parameter S and the flow parameter λ given in Mahros et al. (2023), thus greatly extending the range of these previous solutions. Asymptotic solutions for both large and small values of the Prandtl number σ are derived, showing good agreement with additional numerical integrations. It should be noted that in Mahros et al. (2023), only the case when σ=1 was treated. A solution for large λ when S=1 is obtained, showing a different asymptotic form to the case when S>0 in Mahros et al. (2023). Multiple solutions were seen by them for S<0 and the nature of the lower solution branch as S→0 from below is discussed. The question as to whether the lower branch solutions join as λ>0 when S<0 is resolved through obtaining an asymptotic solution λ small.Originality/valueThe accuracy of the solutions has been checked through a detailed comparison between the solutions obtained numerically and analytically, where excellent agreement has been found. This study is important for scientists working in the area of jet flows to become familiar with the flow properties and behaviour of jets.

Laser-assisted electrohydrodynamic jet printing of hierarchical nanostructure

The hierarchical nanostructures had the advantages of large available space, specific surface area, low density, variable chemical composition, and controllable porosity, and have been widely used in energy, sensor, and catalysis. Traditional methods for preparing hierarchical nanostructures had limitations of a long process, few available materials, and un-customizable size. Electrohydrodynamic jet (E-Jet) printing is a competitive strategy for high-resolution printing. In this paper, a novel laser-assisted E-Jet printing employed a transient high-energy laser effect instead of a traditional continuously thermal effect for printing hierarchical nanostructure. The colorless ZnO ink was prepared with zinc acetate, diethanolamine, PVP, and ethanol. The transient thermal effect of laser irradiation focused a fine jet and induced Taylor cone expansion. The heat accelerated the solvent evaporation and increased the viscous force of the jet. The effects of laser on jet velocity, electric field, and jet behavior were analyzed theoretically. Characterization and 3D morphology of printed nanostructures with and without laser were investigated. The hierarchical nanostructures with size down to 180 nm could be laser-assisted E-Jet printed and its surface area increased multiply. The laser-assisted E-Jet printing method provides a simple, efficient, and low-cost strategy for preparing hierarchical nanostructure, having potential applications in high-performance devices.

Experimental investigation of thermal characteristics of slot synthetic jet impingement on a circular cylinder: Free and constrained environment

The present study aimed to comprehensively investigate the thermal behavior of a slot synthetic jet (SJ) interacting with a circular cylinder in both free and constrained environments through experimental analysis. By traversing the cylinder along the jet centerline across a range of non-dimensional distances (H/w = 5-50), spanning from the near-field to the fully developed region, the research aimed to elucidate the factors governing heat transfer performance. Key parameters such as Reynolds number, jet-cylinder separation distance, and excitation frequency were scrutinized to understand their influence on thermal performance. The SJ was found to perform better in the constrained environment, attributed to relatively higher flow fluctuations developed by the complex interaction of the vortex with the sidewall boundary layer and the cylinder. Almost 12% higher average heat transfer was observed in the case of the constrained environment over the range of parameters employed in the current work. Moreover, a strong dependence of heat transfer on the jet cylinder separation distance was also found. In contrast to the SJ impinging on flat target surfaces where the maximum heat transfer was attained in the intermediate field, at H/w = 14 to 18, for SJ impingement on the circular cylinder, however, this was consistently achieved in the near field, i.e., H/w = 5. Also, the thermal performance as a function of the flow Reynolds number was comparable to the uniform flow case when the Reynolds number was based on the approach flow velocity (i.e., local velocity based on the cylinder location) instead of the velocity at the slot exit.

Effect of nozzle configurations and jet orientations on thermal performance of jet impingement on convex surface

The present study analyze the thermal behaviour of multiple jets impinging on a convex heated surface for two different nozzle geometries (circular and elliptical) and its orientations. Tests are performed with 5 different nozzles at different values of non-dimensional nozzle to surface distance (z/d = 2–10) and Reynolds number (5000–28000). At smaller value of non-dimensional nozzle to plate distance, a distinct pattern of temperature variation is observed that depend on the nozzle shape and orientation, and this pattern diminishes as surface to nozzle distance increases. In the farthest region, elliptical nozzle is found to improve the uniformity (up to 60 %) in Nu variation compared to the circular jets even at the largest surface to nozzle distance. The overall heat transfer is found to increase up to 18 % and the uniformity is found to enhance up to 60 %) for N-2 and N-3 nozzles. An improvement in the thermal performance is observed in the elliptical nozzle in the fountain and impingement zones. The non-uniformity in the Nu behaviour is found to increase with the increase in Reynolds number.

Numerical analysis and industrial practice of single-flow post-combustion oxygen lance with high oxygen supply intensity

The oxygen supply process is a vital operation in converter steelmaking, which is to inject oxygen and kinetic energy into the liquid bath with an oxygen lance. Herein, a single-flow post-combustion oxygen lance (SF-PCL) with four primary holes and six secondary holes was designed to increase the oxygen supply intensity of a 60-ton converter in a steel plant. The attenuation and coalescence behaviors of supersonic jets for the conventional four-hole oxygen lance (COL) and the newly designed SF-PCL were studied by numerical simulation. And then, their metallurgical effects were verified by industrial practice. The simulation results indicated that the SF-PCL effectively suppresses the attenuation and coalescence of supersonic jets as well as simultaneously increases both the impact area and penetration depth. In industrial practice, compared with the COL, the newly designed SF-PCL increases the oxygen supply intensity from the original 4.89 m3 (t·min)−1 to 5.43 m3 (t·min)−1, rises the dephosphorization rate by 1.4%, shortens the blowing time by 34 s, reduces the ferrous charges consumption by 7 kg t−1 and decreases the total iron content in final slag by 0.85%.

Multi-domain analysis and prediction of inductively coupled plasma jet dynamics via high-speed imaging of visible light emission

Inductively coupled plasma wind tunnels are crucial for replicating hypersonic flight conditions in ground testing. Achieving the desired conditions (e.g., stagnation-point heat fluxes and enthalpies during atmospheric reentry) requires a careful selection of operating inputs, such as mass flow, gas composition, nozzle geometry, torch power, chamber pressure, and probing location along the plasma jet. The study presented herein focuses on the influence of the torch power and chamber pressure on the plasma jet dynamics within the 350 kW Plasmatron X ICP facility at the University of Illinois at Urbana-Champaign. A multi-domain analysis of the jet behavior under selected power-pressure conditions is presented in terms of emitted light measurements collected using high-speed imaging. We then use Gaussian Process Regression to develop a data-informed learning framework for predicting Plasmatron X jet profiles at unseen pressure and power test conditions. Understanding the physics behind the dynamics of high-enthalpy flows, particularly plasma jets, is the key to properly design material testing, perform diagnostics, and develop accurate simulation models.

Laser induced spark ignition of a gaseous methane–oxygen model rocket combustor

The spatio-temporal evolution of laser induced spark ignition of non-premixed gaseous methane and oxygen is investigated. The reactants are injected into an optically accessible combustion chamber from an oxidizer centered shear-coaxial injector. High-speed schlieren imaging and measurements of laser energy deposited are used to characterize ignition behavior at various spark locations throughout the chamber. A spatial map of ignition probability is generated from tests at multiple axial and radial locations from the point of propellant injection. The rate of pressure rise from successful tests reveals two modes of ignition dependent on the location of the laser-induced breakdown, direct and indirect, based on laser-induced breakdown occurring within reactant jet or in the recirculation region, respectively. Physical processes occurring over multiple timescales throughout the direct ignition method are first discussed. Ignition outcomes associated with the indirect method are determined by the hydrodynamic ejection protruding from the laser spark, the behavior of which is explored in detail using flow statistics extracted from images taken at a single spark location. The spatial–temporal progression of this jet is found to be dependent on deposited laser energy, leading to a relationship between the amount of energy added to the flow and ignition outcome. General bounds for spark location, deposited laser energy, and ejection behavior are identified to predict ignition outcomes. Cases that are an exception from these bounds are investigated in detail to understand the cause of unique behavior. These cases lie within regions of the variable space that are susceptible to stochastic elements of the flow.Novelty and Significance Statement: This work investigates laser induced spark ignition of O2 and CH4 issuing from a shear-coaxial injector in a model rocket combustor. Probability of ignition as a function of deposited energy and spatial location is studied with high-speed schlieren imaging and pressure measurements. Two distinct ignition modes that have previously not been identified, direct and indirect, are dependent on the laser deposition location with respect to the reactant jet. For indirect cases, where laser deposition is at a distance from the reactants, the hydrodynamic jet ejection generated from the breakdown of the plasma plays a critical role on ignition probability. The behavior of the ejection jet is characterized to provide a phenomenological description of the ignition process. The results of this research show the important interaction between chemical, fluid dynamic, and thermodynamic processes and their impact on laser ignition.

Experimental study of hydrogen jet dynamics: Investigating free momentum and impingement phenomena

There is a growing interest in the utilization of hydrogen (H2), as a zero-carbon fuel, in internal combustion engines (ICEs). Accordingly, the primary focus of this study is to investigate low-pressure H2 jet dynamics, which play a vital role in air-fuel mixing especially in direct injection (DI) engines. High-speed z-type schlieren imaging is employed in a constant volume chamber to study the effect of nozzle geometry (single-hole, double-hole, and multi-hole), pressure ratios (PR = injection pressure (Pi)/chamber pressure (Pch)), injection angle (10°, 15°, and 20°), and injection duration (ID) on the H2 jet characteristics. Image post-processing is executed in MATLAB and Python to extract the H2 jet characteristics, including penetration and cross-sectional area. The novelty stems from the comprehensive investigation of H2 jet dynamics and impingement phenomenon under various engine-like conditions. The results indicate that apart from the fact that higher pressure ratios (PRs) improve the air-fuel mixing, the single-hole nozzle induces the fastest H2 jet penetration and the smallest cross-sectional area. Conversely, the double-hole nozzle leads to the slowest penetration and the most expansive cross-sectional area. The performance of the multi-hole nozzle falls between that of the single-hole and double-hole nozzles. Additionally, changing the injection angle results in jet-piston impingement at the periphery, leading to higher H2 concentration in those areas. This negatively affects the formation of an optimal air-fuel mixture. It is also found that changing the injection duration (ID) has no noticeable impact on the H2 jet's behavior.