Symmetric Jet Research Articles

Numerical simulation on the pressure, turbulence, and λ2$$ {\lambda}_2 $$ vortex characteristics within the annular symmetric jet process under different vacuum degrees

AbstractThe jet impingement flash technology represents a paramount research subject in the domain of heat and mass transfer. To augment its commercial potential, the conjunction of annular multi‐aperture jet impingement with negative pressure flash evaporation is introduced in this study. The employment of an annular nozzle array is integral to the enhancement of the heat and mass transfer efficiency between the phases. The Realizable k‐ε model is used in this study. The negative pressure flash vaporization model was also developed by introducing a mass source term and an energy source term based on the Mixture model. The flow characteristics are characterized using numerical simulation. Additionally, the λ2 vortex identification criterion is investigated the vortex structure. The simulation results exhibit good agreement with experimental findings, demonstrating that a higher initial vacuum leads to a stronger flashing effect and a more chaotic movement of the flow group within the flow field. Thus, this study provides a reference method for the structural design and optimization of annular symmetric jet impingement negative pressure deammonia chemical equipment for engineering applications.

On the role of aortic valve architecture for physiological hemodynamics and valve replacement, Part I: Flow configuration and vortex dynamics

Aortic valve replacement has become an increasing concern due to the rising prevalence of aortic stenosis in an ageing population. Existing replacement options have limitations, necessitating the development of improved prosthetic aortic valves. In this study, flow characteristics during systole in a stenotic aortic valve case are compared with those downstream of two newly designed surgical bioprosthetic aortic valves (BioAVs). To do so, advanced three-dimensional fluid–structure interaction simulations are conducted and dedicated analysis methods to investigate jet flow configuration and vortex dynamics are developed. Our findings reveal that the stenotic case maintains a high jet flow eccentricity due to a fixed orifice geometry, resulting in flow separation and increased vortex stretching and tilting in the commissural low-flow regions. One BioAV design introduces non-axisymmetric leaflet motion, which reduces the maximum jet velocity and forms more vortical structures. The other BioAV design produces a fixed symmetric triangular jet shape due to non-moving leaflets and exhibits favourable vorticity attenuation, revealed by negative temporally and spatially averaged projected vortex stretching values, and significantly reduced drag. Therefore, this study highlights the benefits of custom-designed aortic valves in the context of their replacement through comprehensive and novel flow analyses. The results emphasise the importance of analysing jet flow, vortical structures, momentum balance and vorticity transport for thoroughly evaluating aortic valve performance.

An innovative double-jet design as an air flow barrier to isolate temperature and humidity in a low-temperature storage room

This study used an innovative double-jet design to isolate the temperature and humidity of a lower temperature storage room (-15 °C) from an adjoining higher temperature room (5 °C). This device can reduce the chance of forming a hazardous area in the working environment. Several axial fans are installed on the top of the flow isolation device (FID) to provide an air flow barrier. Those fans blow the air that can induce the Coanda effects outside of the FID. A blockage body is designed and installed in the downstream area on a perforated plate that can divide the flow into two symmetric separated jets. Computational Fluid Dynamics (CFD) is used to simulate the flow pattern with two different practical air velocities, 5 and 5.6 m/s. The results show that the case where the FID is installed in both rooms exhibits the highest isolation efficiency, up to approximately 94% for RH and 93% for temperature. The findings of flow analysis demonstrate that significant amounts of energy can potentially be saved. The practical implications of these findings could be in food and pharmaceuticals industries.

Influence of primary jets on the combustion performance of a rich quench lean combustor: A numerical and experimental investigation

The effect of primary hole jet on the Rich-burn/Quick-mix/Lean-burn (RQL) combustor was studied here by both experimental and numerical analysis approaches, where with a standard k-ε model was applied. To understand the influence of primary hole on the performance of RQL combustor, three primary hole jets configurations with different dimensions of layout were tested. Results from both experimental and numerical studies demonstrate that an increased number of primary holes results in a moderated reduction in the height of the central recirculation zone and the emergence of vortical structures in the quenched zone. Additionally, in the rich fuel region, the flame area decreases with additional primary holes when the equivalence ratio is below 1.0, while it expands when the equivalence ratio exceeds 1.0. The interaction between local recirculation zones is enhanced by additional primary holes, facilitating rapid fuel-air mixing and reducing circumferential ignition time. Notably, a symmetric jet flow scheme with fewer primary holes displays a favorable outlet temperature distribution, characterized by a weighted standard deviation ranging from 0.02 to 0.06, indicating efficient mixing. These comprehensive insights highlight the intricate relationship between primary hole jets and combustor performance.

Vortex of a Symmetric Jet Structure in a Natural Gas Pipeline via Proper Orthogonal Decomposition

The impact of particle addition jets on the flow field in natural gas pipelines was investigated, and the structural information of the flow field at different flow velocities in a symmetric jet flow was analyzed via numerical simulation. The results of coherent structures in the high-pressure natural gas pipeline reveal vortex structures of varying sizes both upstream and downstream of the jet flow. To determine the spatial distribution of the main vortex structures in the flow field, proper orthogonal decomposition (POD) mode analysis was performed on the unsteady numerical results. Moreover, the detailed spatial characteristics of the coherent vortex structures represented by each mode were obtained. The results indicate that the large-scale vortex structures within the pipeline are balanced and stable, with their energy increasing as the jet flow velocity increases. Additionally, higher-order modes exhibit significant shedding of small-scale vortex structures downstream of the jet flow. In this research, coherent structures present in symmetric particle addition jets are provided, offering theoretical support for future investigations on the distribution of particle image velocimetry (PIV) flowmeters.

Multi-scale proper orthogonal decomposition (mPOD) analysis of vortex evolution and viscous dissipation in a circular-cylinder wake controlled by parallel symmetric jets

This paper describes a novel flow control scheme over circular-cylinder wakes using parallel symmetric jets. The effects of different jet momentum coefficients (Cm) at θ = ±30° on vortex evolution and viscous dissipation in the circular-cylinder wake are experimentally investigated using high-speed particle image velocimetry (PIV) in an open-jet wind tunnel at a Reynolds number of 1.01 × 104. Multiscale proper orthogonal decomposition (mPOD) is used to analyze the evolution of coherent structures and establish the relationship between flow structures and viscous dissipation. At Cm ≤ 0.0089, the vortex formation length is elongated and the scale and intensity of the vortex are suppressed. Small-scale jet vortices are then generated by the interaction between the jet shear layers at Cm = 0.0174, whereupon the turbulent kinetic energy attains a minimum and the Reynolds shear stress in the wake is basically eliminated. At higher values of Cm, band-like jet oscillations appear in the wake, increasing the turbulence intensity. The inhibition effect of the jets on the wake vortex decreases the viscous dissipation in the wake, with optimal viscous dissipation control obtained at Cm = 0.0089. When Cm > 0.0089, the coupling between the jets increases the viscous dissipation of small-scale, high-frequency turbulent structures, and this effect gradually becomes more obvious with increasing Cm.

HST-1 as a window into the energetics of the jet spine of M 87

We present a new interpretation of the optical knot, HST-1, in the jet of M 87. High-sensitivity 22 GHz Very Large Array images have located HST-1 to within 6 mas of the jet axis immediately upstream. Based on 1.7 GHz Very Long Baseline Array images of a bright flare in 2005, we see that preponderance of emission in the early stages originates from an elongated region that is tilted 12.5° from the jet axis. The superluminal motion, shape, location, and the large jet-aligned optical/UV polarization suggest an identification with the putative relativistic spine of the jet. As such, energy flux estimates for HST-1, ∼870 mas from the nucleus, published in 2006, indicate that the central engine injected, Qspine ≈ 2.5 × 1041 ergs s−1, into the base of the spine about 200 yr earlier. Furthermore, previous studies have revealed a tubular protonic jet on sub-mas scales that envelopes a low luminosity core, presumably the faint spine base. It was estimated that the central engine injected, Qtubular jet ≈ 6.1 × 1041 ergs s−1, about 1.5 yr earlier. If one component of the jet is inherently more powerful, a firm constraint on total jet power in the recent past would then exist. If the emitted jet is inherently dominated by the spine (tubular jet), then the total bilaterally symmetric jet power emitted from the central engine was < 4Qspine ≈ 1.0 × 1042 ergs s−1 (< 4Qtubular jet ≈ 2.4 × 1042 ergs s−1) ∼200 (∼1.5) yr earlier. Assuming a nearly constant central engine injected jet power for ∼200 yr indicates a total jet power of ≲2 × 1042 ergs s−1 in epochs of modern observation or ≲3.5% jet production efficiency for an accretion rate of 0.001 M⊙ yr−1. Seemingly, the focus of Event Horizon Telescope Collaboration (EHTC) numerical models should be biased toward jet powers of ≲2 × 1042 ergs s−1, as opposed to larger estimates from ejections many centuries or millennia earlier.

Numerical study on mixing characteristics of symmetrical and asymmetrical twin jets

Numerical study on mixing characteristics of symmetrical and asymmetrical twin jets

Assessing the Structure-Based Turbulence Model Performance for Thermal Striping Applications Using Symmetric Jet Experiments

Turbulent mixing of coolant streams can result in an oscillatory mixing phenomenon called thermal striping. These fluctuations have the potential to lead to anticipated thermal fatigue failures in advanced nuclear reactors. To predict thermal striping, robust and computationally affordable modeling tools that are capable of accurately representing complex turbulence are needed. Hybrid turbulence approaches, such as detached-eddy simulation and scale-adaptive simulation, have shown some success in resolving complex unsteady turbulence for massively separated flows, however the applicability of these models to internal flows is limited. A STRUCTure-based (STRUCT) second-generation Unsteady Reynolds-Averaged Navier–Stokes turbulence model was recently proposed at the Massachusetts Institute of Technology to robustly extend the applicability of hybrid closures. In this work, the STRUCT model is evaluated using experimental data taken at the Reactor Cavity Cooling System separate-effects test facility at the University of Michigan. The experiments observed the interaction of parallel symmetric rectangular jets, and include measurements for mean profiles of velocity and Reynolds stresses. In the present work, the simulation results are assessed against mean profiles of velocity and Reynolds stresses, demonstrating the ability to reproduce the unsteadiness of the jets in close agreement with the measurements at considerably reduced computational cost.

Investigation on spatial distribution of atomic density in a supersonic planar symmetric gas jet by simulations

As a special gas target with large aspect ratio, the planar symmetric gas jet has attracted some interests in High Harmonic Generation (HHG). It can be produced by gas adiabatic expansion through a supersonic slit nozzle into vacuum. In this work, the spatial distributions of atomic density are investigated in detail along the short side, the long side and the gas jet flow of the planar symmetric argon gas jet based on ANSYS Fluent. The results indicate that along the long side, the planar symmetric jet provides the advantages of high atomic density and the large dimension of uniform atomic density distribution. The density distribution profile is similar to the Gaussian one along the short side. The atomic density at the center of the jet outside the nozzle is lower and decreases much faster than that expected by idealized straight streamline model due to the lateral expansion of gas jet at slit nozzle width.

Modeling and Performance Analysis of Municipal Solid Waste Treatment in Plasma Torch Reactor

Thermal plasma has emerged as a technology with tremendous promise for municipal wastes that should be disposed of sustainably. A numerical simulation of a symmetric turbulent plasma jet from a thermal air plasma torch was developed using COMSOL Multiphysics®5.4 engineering simulation software. The velocities, temperature, arc root motion, and joule heating of the plasma jet were examined under the impact of the gas mass flow rate and current. Moreover, the electrical power required for the municipal solid waste (MSW) processing was estimated. The enthalpy and the effectiveness of the plasma torch were analyzed and discussed. Subsequently an investigation was conducted into the gasification characteristics of MSW using air and steam gases. The torch’s power and efficiency could be enhanced with a higher mass flow rate and temperature. Three operating modes were identified from the current–arc flow combination. Among the plasma gas considered, the air gas plasma torch guarantees an acceptable thermal efficiency and a low anode erosion rate. Plasma gasification produces cleaner syngas with higher efficiency (84%) than the conventional process due to the elevated temperature used during the process that breaks down all the char, dioxins, and tars.

Vibration-induced streaming flow near a sharp edge: Flow structure and instabilities in a large span of forcing amplitude.

The steady streaming generated near solid walls by the periodic forcing of a viscous fluid is known to be strongly enhanced near sharp structures, owing to centrifugal effects that lead to the generation of an intense jet from the sharp tip. This flow has been shown to provide efficient active mixing in microchannels, due to strong transverse velocity. The forcing is often prescribed by acoustic transducers, but it can also be generated from low-frequency time-periodic flow ensured by mechanical vibrations. In this paper, we study the flow structure generated by low-frequency forcing (typically 10Hz) around a sharp tip. Using direct numerical simulations, we extract both the time-periodic and steady responses within a large span of amplitude of vibrations. When the amplitude is smaller than the tip radius of curvature, we recover the flow structure observed at higher frequencies (>1kHz) in previous studies, namely, an intense symmetric central jet and a quadratic dependence for the characteristic streaming velocity with the oscillating velocity v_{s}∼v_{a}^{2}. At higher amplitudes, such a scaling no longer holds and the streaming flow pattern loses its left-right symmetry. We then analyze the mechanisms of the instability from the careful examination of the instationary flow fields, and we propose possible mechanisms for such a flow transition involving the coupling between the streaming jet and instationary vorticity.

Symmetric differentials and Jets extension of L^2 holomorphic functions

Symmetric differentials and Jets extension of L^2 holomorphic functions

EXPERIMENTAL INVESTIGATION OF UNLIKE TRIPLET SPRAYS USING HIGH-MAGNIFICATION SHADOWGRAPHY: INFLUENCE OF THE JETS VELOCITIES AND CENTRAL JET PROPERTIES

In this study, inert liquid sprays are generated by impinging two symmetric jets of water with a central jet of water, ethanol, or n-dodecane. This configuration, referred to as an unlike triplet injector, can be used in rocket engines to atomize liquid storable propellants, for instance, hydrogen peroxide oxidizer combined to a fuel. Here, the inert sprays are investigated in the so-called impact waves regime, which corresponds to jets a Weber number of higher than 1000. The atomization process is characterized using high-magnification shadowgraphy (HMS) from the impinging point of the jets into a sheet until it breaks up into ligaments and droplets. The HMS technique enables 10 kHz visualizations with an interframe of 4 μs and a spatial resolution up to 6.4 μm/pixel (1024 × 1024 pixels). Characteristic lengths of the primary atomization are measured: breakup length, apparent wavelength, and ligaments size. Similarly, the droplet populations are described based on arithmetic and Sauter mean diameters, shape, and velocity. Statistics of large droplet distributions are analyzed regarding the injection conditions and distance to the impingement point. Compared to like-doublet spray, the like-triplet evidences a slower atomization (longer breakup distance) and generates larger drops that require more distance to stabilize in size, centricity, and velocity. Unlike-triplet sprays exhibit a similar behavior to like-triplet spray while producing larger droplets, probably because of the fuel properties that stabilize the liquid sheet.

Acoustic analysis of jet atomization for uniform dispersion of nano- and micro-droplets

In this study, the mechanisms of jet atomization were analyzed based on a frequency analysis of atomization sounds in the audible range (∼20 kHz). Jet atomization is a two-dimensional, high-speed atomization using a diaphragm, and interesting acoustic signals and atomization phenomena were detected on hydrophobic and hydrophilic diaphragms. The hydrophilic diaphragm strongly interacted and resonated with the surface wave, resulting in symmetrical jet atomization relative to the diaphragm. The resonance between the diaphragm and the surface wave was supported by a calculation of the eigenfrequency of the diaphragm and the coincidence of the droplet diameters as calculated from Lang's equation. Notably, the diaphragm excited by the ultrasonic transducer acted as a new transducer vibrating perpendicular to the transducer. As a result, when the diaphragm and the surface wave were in resonance at 2.4 MHz, a symmetrical two-dimensional high-speed jet atomization was generated in the direction perpendicular to the transducer’s vibration direction. This study also revealed that the atomization state can be determined based on the acoustic analysis. This acoustic analysis of atomization sounds can be applied in more advanced atomization control, such as for providing uniform dispersions of droplets containing DNA, drugs, or microplastics.

Solution of Temperature Fluid Particle in Incompressible Dusty Fluid with The Effect of Week Induced Magnetic Field

It is possible for dust particles to naturally exist in fluids. In the study of fluid mechanics, these problems related to flow characteristics of temperature. How the magnetic field of suspended particulate matter affects the temperature axially symmetrical jet mixing of incompressible dusty fluid. we assume that the velocity and temperature in the jet deviate from the surrounding stream. To linearize the equation that was solved using Laplace Transformation, a perturbation method was used. The solution of temperature of the particle phase which is depends on fluid phase temperature with in the weak induced Magnetic field.

Pressure distribution on a flat plate in the context of the phenomenon of the Coanda effect hysteresis

As a result of the Coanda effect, a symmetrical free jet will flow as an asymmetrical wall jet. At the same time, at the obstacle along which the flow is observed, the wall jet generates pressure distribution. In this study, the obstacle located at the diffuser outlet is a flat plate with a variable inclination angle. The article presents results of the study on pressure distributions on a flat plate with a variable angle of inclination. In the experiment, the Reynolds number ranged from 16,192 to 42,240. A fixed geometry diffuser (Witoszyński nozzle) with a height of 0.60 m, width of 0.02 m and outlet velocity of 11.33–29.57 m/s was used. A plate with a length of 1.00 m and a variable inclination angle was installed at the diffuser outlet. What is new, however, is that the presented results of the experimental research include the influence of the Coanda effect hysteresis on the pressure distribution on the plate. The article shows how pressure distributions change on the plate depending on whether the initial angle of inclination was 0° and was increased gradually in the course of the experiment until a detachment of the jet flowing from the plate was observed, or the initial angle of inclination was close to 90° in the primal state and as the angle of the plate inclination was decreased, the jet flowing towards the plate reached the state of attachment to the plate surface. The study demonstrated that for a turbulent jet, pressure distribution on a flat plate is determined not only by the plate’s inclination angle, but also by the direction of its rotation.

High Resolution Ambient MS Imaging of Biological Samples by Desorption Electro-Flow Focussing Ionization.

In this study, we examine the suitability of desorption electro-flow focusing ionization (DEFFI) for mass spectrometry imaging (MSI) of biological tissue. We also compare the performance of desorption electrospray ionization (DESI) with and without the flow focusing setup. The main potential advantages of applying the flow focusing mechanism in DESI is its rotationally symmetric electrospray jet, higher intensity, more controllable parameters, and better portability due to the robustness of the sprayer. The parameters for DEFFI have therefore been thoroughly optimized, primarily for spatial resolution but also for intensity. Once the parameters have been optimized, DEFFI produces similar images to the existing DESI. MS images for mouse brain samples, acquired at a nominal pixel size of 50 μm, are comparable for both DESI setups, albeit the new sprayer design yields better sensitivity. Furthermore, the two methods are compared with regard to spectral intensity as well as the area of the desorbed crater on rhodamine-coated slides. Overall, the implementation of a flow focusing mechanism in DESI is shown to be highly suitable for imaging biological tissue and has potential to overcome some of the shortcomings experienced with the current geometrical design of DESI.

On the mechanism of ionization of atoms at compression of a substance by front of the converging shock wave

Purpose. To study changes in the microstructure of metals after exposure to high-energy plasma jets formed by the cumulation of gas-dynamic flows in a conical target. To estimate the expected state of matter in a strong shock wave compression, taking into account the change in volumetric energy density at the moment of transformation of a solid body plasma into nuclear matter. Methodology. The technique of laser initiation of a profiled front of detonation waves in explosive charges and the corresponding profile of shock waves in materials, methods and techniques for measuring the dynamic parameters of shock-compressed substances are used. Findings. An experimental study on the physicochemical state of a substance that has been processed with extremely high pressures and temperatures during compression by converging shock waves in conical targets has been carried out. Scientific results of physical and mathematical modelling of converging shock waves are analysed. Originality. For the first time, the formation of symmetric plasma jets during gas compression in conical targets has been experimentally observed. For the first time, metallo-physical studies on the microstructure of cast iron and steel have been carried out. These studies were made after the action of high-energy dense plasma jets with a temperature of (2.52.8) × 106K and a pressure 1.12 × 1012 arising from the collision of the jet with a barrier. Iron-55 and copper-64 isotopes were found in the cast iron microstructure near the surface formed by the action of the plasma jet. The main components of the plasma jet were gaseous oxygen, nitrogen, argon, and atomic iron, copper and gold. The fact of formation of isotopes is the result of nuclear reactions. One of the main conditions for the implementation of such reactions is a dense high-temperature plasma. It is assumed that under the action of a strong shock wave in a conical target, in addition to the synthesis reaction, other nuclear reactions with heavy elements can be realized. The ideas about the expected state of matter in a compression shock wave are presented, taking into account the change in the volumetric energy density at the moment of transformation of a solid body plasma into nuclear matter. Practical value. The proposed technique for conducting experimental studies on a shock-compressed substance under the action of extreme temperatures and pressures in conical targets using laser initiation of chemical explosives is of practical importance. The idea of the expected state of matter in the shock wave is also important.

Effect of thermal buoyancy on vortex ring air supply mode

Owing to the air buoyancy effect in the non-isothermal environment, the air supply efficiency will be greatly reduced due to the severe interference of the air distribution and air supply performance. Although the vortex ring air supply mode shows better air supply efficiency than the symmetrical round jet under the isothermal conditions, it is still unclear under non-isothermal conditions. Therefore, the dynamic mesh method is applied to the formation of the air vortex ring. Then the influence of non-isothermal conditions on the transport characteristics of the air vortex ring is studied, and the temperature attenuation trend of the vortex ring air supply mode are evaluated. The results show that the attenuation of the translational velocity of the vortex ring under isothermal conditions can be used to approximate the translational velocity of the thermal air vortex ring, with a deviation of no more than 3%; second, the vortex ring air supply mode has better directionality, and the deviation can be reduced by 85% compared with the symmetrical round jet; third, an improvement method of the vortex ring air supply mode is proposed, the vortex core temperature increased by 4.5 °C; finally, the temperature attenuation of the thermal vortex ring is 25.8% lower than that of the thermal jet in the range of Lpath/D < 20.