Jet Phenomenon Research Articles

Experimental study and large Eddy simulation of a coaxial jet with perforated obstacles to control thermal mixing characteristics

ABSTRACTThermal mixing phenomena of a coaxial jet with perforated obstacles are analyzed both experimentally and numerically. Perforated obstacles are used in front of a coaxial jet that has different temperatures of the fluid to control the thermal mixing behavior. An experimental set-up was constructed to perform several cases and all cases are simulated by using large eddy simulation (LES) turbulence model. Results of the study presented that inserting perforated obstacle affects the mixing performance positively and the best mixing performance is obtained in the case that the obstacle has the highest permeability. Experimental and computational results were compared and a good agreement was obtained.

Experimental and mathematical study of the spray flash evaporation phenomena

Spray flash evaporation is a promising way that potentially enables various renewable energy sources to be employed for desalination. This paper specifically studies the flash evaporation phenomenon of a hot water jet sprayed into a low-pressure chamber. Special considerations are rendered to the flash evaporation process under lower temperature differences which evolves higher thermal efficiency and better low-grade heat utilization for desalination. An experimental setup has been developed and temperature profiles of the sprayed water in the axial direction are mapped. Under low flow velocity conditions, the water jet shatters into droplets due to the flash atomization effect. Such a shattering phenomenon can be captured and quantified by a mathematical model based on droplet analysis. Applying this model, the temperature profiles are translated into the mean spray droplet diameters. The effect of different variables on the flash evaporation process is further investigated. Key results revealed that the mean droplet diameters of the spray are several orders of magnitudes smaller than the nozzle diameter. Such fine droplets allow complete evaporation to be accomplished within 50 cm from the nozzle exit, enabling a compact evaporator design. Additionally, higher initial temperature differences and higher flow velocities reduce the mean droplet diameter to be smaller than 300 μm, and the corresponding vertical distance required to complete the evaporation process is shorter than 10 cm.

The different energy loss mechanisms of inclusive and b-tagged reconstructed jets within ultra-relativistic heavy-ion collisions

The phenomenon of jet quenching provides essential information about the properties of hot and dense matter created in ultra-relativistic heavy-ion collisions. Recent results from experiments at the Large Hadron Collider (LHC) show evidence for an unexpectedly similar suppression of both light and heavy flavor jets. Furthermore, the role of radiative energy loss of heavy quarks is still under active discussion within the theoretical community. By employing the parton cascade Boltzmann Approach to Multi-Parton Scatterings (BAMPS), which numerically solves the 3+1 D Boltzmann equation both for light and heavy flavor partons, we calculate the nuclear modification factor of inclusive and b-tagged reconstructed jets in 0–10% central sLHC=2.76 A TeV Pb + Pb collisions. Based on perturbative QCD cross sections we find a suppression of both light and heavy flavor jets. While the inclusive jets are slightly too strong suppressed within Bamps in comparison with data, both elastic + radiative and only elastic interactions lead to a realistic b-tagged jet suppression. To further investigate light and heavy flavor energy loss we predict the R dependence of inclusive and b-tagged jet suppression. Furthermore, we propose the medium modification of b-tagged jet shapes as an observable for discriminating between different heavy quark energy loss scenarios.

Observational study on the fine structure and dynamics of a solar jet. I. Energy build-up process around a satellite spot

Abstract We report on a solar jet phenomenon associated with successive flares on 2014 November 10. These explosive events were involved with the satellite spots’ emergence around a δ-type sunspot in the decaying active region NOAA 12205. The data for this jet were provided by the Solar Dynamics Observatory, the X-Ray Telescope aboard Hinode, and the Interface Region Imaging Spectrograph and Domeless Solar Telescope at Hida Observatory, Kyoto University. These abundant data enabled us to present this series of papers to discuss the entire process of the observed phenomena, including the energy storage, event trigger, and energy release. In this paper, we focus on the energy build-up and trigger phases, by analyzing the photospheric horizontal flow field around the active region by an optical flow method. The analysis shows the following results: (1) The observed explosive phenomena involved three satellite spots, the magnetic fluxes of which successively reconnected with their pre-existing ambient fields; (2) All of these satellite spots emerged in the moat region of a pivotal δ-type sunspot, especially near its convergent boundary with the neighboring supergranules or moat regions of adjacent sunspots; (3) Around the jet ejection site, the positive polarities of the satellite spot and adjacent emerging flux encountered the global magnetic field with a negative polarity in the moat region of the pivotal δ-type sunspot, and thus the polarity inversion line was formed along the convergent boundary of the photospheric horizontal flow channels.

Experimental Investigation of Thermal-Mixing Phenomena of a Coaxial Jet with Cylindrical Obstacles

In this study, the thermal-mixing phenomenon of a coaxial jet with cylindrical obstacles is analyzed experimentally. Cylindrical obstacles are located in front of the coaxial jet to control the thermal-mixing behavior. A coaxial-jet nozzle designed and inserted into a rectangular cross section confined channel. The coaxial jet consists of two water jets at different temperatures that were positioned on the same axis. An experimental setup was constructed to perform two different obstacle combinations and the standard case having no obstacles. These three cases were performed with six different boundary conditions. Also, a comparison of experimental results with available numerical results shows a good agreement. The obtained results indicate that the mixing performance of cold and hot fluids is a function of temperature difference, and it increases as the temperature difference between jets increases. Inserting obstacles has significant effects on the mixing performance, and these effects of obstacle change with increasing temperature difference between cold and hot jets. Locating various combinations of obstacles in the mixing channel does not affect the dominant frequency that is found as 5 Hz. On the other hand, using cylindrical obstacles may change the magnitude of thermal fluctuations after them. Consequently, this study exposed that the chosen parameters have remarkable effects on the mixing behavior of the coaxial jet, and these parameters can be used to control the mixing phenomenon.

PIV Measurements in the Near and Intermediate Field Regions of Jets Issuing from Eight Different Nozzle Geometries

An experimental study was conducted to investigate the effect of nozzle geometry on the mixing characteristics and turbulent transport phenomena in turbulent jets. The nozzle geometry examined were round, square, cross, eight-corner star, six-lobe daisy, equilateral triangle as well as ellipse and rectangle each with aspect ratio of 2. The jets were produced from sharp linear contoured nozzles which may be considered intermediate to the more widely studied smooth contraction and orifice nozzles. A high resolution particle image velocimetry was used to conduct detailed velocity measurements in the near and intermediate regions. It was observed that the lengths of the potential cores and the growth rates of turbulence intensities on the jet centerline are comparable with those of the orifice jets. The results indicate that the decay and spreading rates are lower than reported for orifice jets but higher than results for smooth contoured jets. The jets issuing from the elliptic and rectangular nozzles have the best mixing performance while the least effective mixing was observed in the star jet. The distributions of the Reynolds stresses and turbulent diffusion clearly showed that turbulent transport phenomena are quite sensitive to nozzle geometry. Due to the specific shape of triangular and daisy jets, the profiles of mean velocity and turbulent quantities are close to each other in their minor and major planes while in the elliptic and rectangular jets are considerably different. They also exhibit more isotropic behavior compared to the elliptic and rectangular jets. In spite of significant effects of nozzle geometry on mean velocity and turbulent quantities, the integral length scales are independent of changes in nozzle geometry.

Photonic jet μ-etching: from static to dynamic process

Photonic jet etching is a direct-laser etching method applying photonic jet phenomenon to concentrate the laser beam onto the proceeded material. We call photonic jet the phenomenon of the localized sub-wavelength propagative beam generated at the shadow-side surfaces of micro-scale dielectric cylinders or spheres, when they are illuminated by an electromagnetic plane-wave or laser beam. This concentration has made possible the laser to yield sub-μ etching marks, despite the laser was a near-infrared with nano-second pulses sources. We will present these achievements from the beginning when some spherical glasses were used for static etching to dynamic etching using an optical fiber with a semi-elliptical tip.

Large-volume excitation of air, argon, nitrogen and combustible mixtures by thermal jets produced by nanosecond spark discharges

This work presents experimental observations of strong expanding thermal jets following the application of nanosecond spark discharges. These jets propagate in a toroidal shape perpendicular to the interelectrode axis, with high velocities of up to 30 m s−1 and over distances of the order of a cm. Their propagation length is much larger than the thermal expansion region produced by the conventional millisecond sparks used in car engine ignition, thus greatly improving the volumetric excitation of gas mixtures. The shape and velocity of the jets is found to be fairly insensitive to the shape of the electrodes. In addition, their spatial extent is found to increase with the number of nanosecond sparks and with the discharge voltage, and to decrease slightly with the pressure between 1 and 7 atm at constant applied voltage. Finally, this thermal jet phenomenon is observed in experiments conducted with many types of gas mixtures, including air, nitrogen, argon, and combustible CH4/air mixtures. This makes nanosecond repetitively pulsed discharges particularly attractive for aerodynamic flow control or plasma-assisted combustion because of their ability to excite large volumes of gas, typically about 100 times the volume of the discharge.

Acoustojet: acoustic analogue of photonic jet phenomenon based on penetrable 3D particle

It has been demonstrated for the first time that an existence of acoustic analogue of photonic jet phenomenon, called acoustojet, providing for subwavelength localization of acoustic field in the shadow area of arbitrary 3D penetrable mesoscale particle, is possible.

Performance analysis of a horn-type rudder implementing the Coanda effect

The Coanda effect is the phenomenon of a fluid jet to stay attached to a curved surface; when a jet stream is applied tangentially to a convex surface, lift force is generated by increase in the circulation. The Coanda effect has great potential to be applied practically applied to marine hydrodynamics where various lifting surfaces are being widely used to control the behavior of ships and offshore structures. In the present study, Numerical simulations and corresponding experiments were performed to ascertain the applicability of the Coanda effect to a horn-type rudder. It was found that the Coanda jet increases the lift coefficient of the rudder by as much as 52% at a jet momentum coefficient of 0.1 and rudder angle of 10°.

Visualization movie analysis of acoustic phenomena of a supersonic jet and Its comparison with intensity vectors

The authors have studied the acoustic wave from an unheated, Mach 1.8 ideally expanded jet by using the acoustic intensity vector measurement and analysis of high-speed schlieren visualization movies (for example, the Fourier transform and wavelet-based conditional sampling). Both these techniques reveal the characteristics of the acoustic wave, such as the propagation direction and location of a source region. These techniques have their own advantages: the quantitative data can be obtained by using the acoustic intensity vector measurement, whereas the acoustic field including a close region to the jet can be visualized with high spatial resolution by using the Schlieren movie analysis. Therefore, their comparison is a meaningful approach to understand the acoustic phenomenon. This presentation compares these two techniques and describes what can be discussed with their comparison, considering the advantage and disadvantage of each measurement technique.

Experimental study and Large Eddy Simulation of thermal mixing phenomena of a parallel jet with perforated obstacles

Thermal mixing and flow field due to two parallel jets which have different temperatures are investigated both experimentally and numerically. The perforated passive obstacles are used with different geometrical specifications. They are located in front of the jets to control flow field and mixing behavior of the jets. An experimental setup designed and manufactured and Large Eddy Simulation turbulence model with the WALE subgrid-scale stress model were used to simulate same experimental conditions. Three perforated obstacles (POs) with different porosity values were used in the study and these obstacles inserted into a rectangular cross-section confined channel. Results demonstrated that increasing the values of temperature differences enhance thermal mixing performance along the channel. The best mixing quality was captured at the same flow rates of the jets. The perforated obstacle has significant positive effect on the mixing performance and this effect increase with higher porosity values. Dominant frequency of mixing region was found as 5 Hz in all cases. The temperature profiles showed that as porosity decreases thermal oscillations are starting to reach the wall. Both 2D and 3D velocity profiles demonstrated that using of POs reduces the domination of turbulence area in the channel.

A new visual tracking method for the analysis and characterization of jet flow

In this paper, we develop a new method to track the evolution of bubbles or droplets in jet flow. Proposed tracker fuses shape and motion features of the individually detected droplets in 2D shadow images and employs the Bhattacharyya distance to assign the closest one among candidate droplet regions. Distinct from the existing droplet tracking techniques in the literature, shapes of the target droplets were not assumed to be circles or ellipses. Instead evolving droplet contours were extracted and analyzed. Proposed tracking algorithm could achieve real time performance with 16fps in MATLAB environment. Single, double and triple droplets were tracked with the average accuracy of 87%, 87% and 83%, respectively. Experimental results were then evaluated to explain the underlying jet phenomena.

Numerical Simulation and Experimental Tests on Explosively-Induced Water Jet Phenomena

This study addresses some aspects regarding water jet propulsion during high explosives detonation. A number of theoretical and experimental studies have shown that using Gurney equation and the relationships derived, one can provide fair results regarding initial velocity of metallic fragments for explosively-driven metal casings. However, an investigation on Gurney equations utilization for the prediction of water velocity has not been performed yet. By carrying out simple experimental tests and numerical simulations, water has been investigated in terms of total mass average velocity and tip velocity. Based on the available data, the findings indicate that Gurney equations overestimate the water mass average velocity. For water tip velocity evaluation, further studies should be made.

Solar Coronal Jets: Observations, Theory, and Modeling.

Chromospheric and coronal jets represent important manifestations of ubiquitous solar transients, which may be the source of significant mass and energy input to the upper solar atmosphere and the solar wind. While the energy involved in a jet-like event is smaller than that of "nominal" solar flares and Coronal Mass Ejections (CMEs), jets share many common properties with these major phenomena, in particular, the explosive magnetically driven dynamics. Studies of jets could, therefore, provide critical insight for understanding the larger, more complex drivers of the solar activity. On the other side of the size-spectrum, the study of jets could also supply important clues on the physics of transients close or at the limit of the current spatial resolution such as spicules. Furthermore, jet phenomena may hint to basic process for heating the corona and accelerating the solar wind; consequently their study gives us the opportunity to attack a broad range of solar-heliospheric problems.

Three-dimensional shock wave distortion in shock-square vortex loop interaction

Understanding of the three-dimensional shock wave-vortex loop interaction phenomena plays a key role in noise reduction. This study focuses on the three-dimensional shock wave distortion and propagation phenomena in a near-field supersonic jet. Shock-square vortex loop interaction was experimentally investigated in a square cross-sectional open-end shock wave generating tube at an incident shock Mach number of 1.39±0.05. A square vortex loop impinged on a reflected shock wave from a wall located in front of the nozzle end. The planar reflected shock wave transforms into either a concave or convex distorted shape due to the opposing high-speed flow emitted from the nozzle corner. The convex shaped shock wave scatters towards the outside of the vortex loop, whereas the concave one converges towards the centre of the vortex loop. The concave shaped shock wave results in shock wave focusing. In shock-square vortex loop interaction, the shock wave is locally focused along the axis of the nozzle corner.

Steady and unsteady calculations on thermal striping phenomena in triple-parallel jet

The phenomenon of thermal striping is encountered in liquid metal cooled fast reactors (LMFR), in which temperature fluctuation due to convective mixing between hot and cold fluids can lead to a possibility of crack initiation and propagation in the structure due to high cycle thermal fatigue. Using sodium experiments of parallel triple jets configuration performed by Japan Atomic Energy Agency (JAEA) as benchmark, numerical simulations were carried out to evaluate the temperature fluctuation characteristics in fluid and the transfer characteristics of temperature fluctuation from fluid to structure, which is important to assess the potential thermal fatigue damage. In this study, both steady (RANS) and unsteady (URANS, LES) methods were applied to predict the temperature fluctuations of thermal striping. The parametric studies on the effects of mesh density and boundary conditions on the accuracy of the overall solutions were also conducted. The velocity, temperature and temperature fluctuation intensity distribution were compared with the experimental data. As expected, steady calculation has limited success in predicting the thermal–hydraulic characteristics of the thermal striping, highlighting the limitations of the RANS approach in unsteady heat transfer simulations. The unsteady results exhibited reasonably good agreement with experimental results for temperature fluctuation intensity, as well as the average temperature and velocity components at the measurement locations.

REVERBERATION MAPPING OF THE GAMMA-RAY LOUD NARROW-LINE SEYFERT 1 GALAXY 1H 0323+342

ABSTRACT Recently, 1H 0323+342 has attracted a lot of attention as one of several narrow-line Seyfert 1 galaxies detected in the γ-ray band. To understand their central energy engines and jet phenomena, the black hole mass is important. We made use of the Lijiang 2.4 m Telescope to monitor 1H 0323+342 for more than two months. This galaxy is one of the candidates for a monitoring project of super-Eddington accreting massive black holes. The reverberation mapping shows that Hβ emission has a delayed response of days with respect to the SDSS g′ light curve in the rest frame. The optical Fe ii variations were detected after subtracting host contaminations, and a reverberation with a delay of days was found in the rest frame. By assuming the viral factor f BLR = 6.17 for the broad-line region (BLR) velocity characterized by FWHM because of the face-on orientation, we find that the black hole mass derived from Hβ is , and the accretion rate is , where , is the mass accretion rate, L Edd is the Eddington luminosity, and c is the speed of light. This black hole is one order less massive than that given by the Magorrian relation from the bulge mass. We test the relation between accretion rates and radio-loudnesses in all mapped radio-loud active galactic nuclei, and find that 1H 0323+342 falls within this group.

On the mechanism of boiling heat transfer enhancement by surfactant addition

In our previous study, bubble jet and bubble explosion around a heated wire were discovered in aqueous cetyltrimethyl ammonium chloride (CTAC) solutions (Wang et al., 2016), in which the bubble explosion process was explained. The bubble explosion phenomenon was proven to be a failed coalescence of unstable bubbles which caused local disturbance and enhanced boiling heat transfer. In this paper, comparative experiments of boiling around a heated wire for different types of surfactant solutions, ethanol and silicone oil were carried out in order to explore the mechanism of surfactant addition enhancing boiling heat transfer. All these fluids had lower surface tensions than that of water. Cationic surfactant of CTAC, anionic surfactant of sodium dodecylbenzenesulfonate (SDBS) and nonionic surfactant of alkyl polyglycoside (APG) were used. Bubble jet and bubble explosion phenomenon were found in all three kinds of surfactant solutions, exhibiting excellent heat transfer effect. For the pool boiling in ethanol, only bubble jet around the heated wire was found, showing better heat transfer efficiency than water. However, weaker boiling heat transfer occurred in silicone oil without bubble jet and bubble explosion. Due to the heat sensitivity characteristics, APG solution had a lower critical heat flux (CHF) than water, while CTAC and SDBS solution had higher CHF. With all phenomena and heat transfer performances, the mechanism of boiling heat transfer enhancement by surfactant addition was confirmed, i.e., the bubble jet and bubble explosion process enhanced the boiling heat transfer in surfactant solution rather than low surface tension.

Taper of kerfs made in rocks by abrasive water jet (AWJ)

The taper, inclination of cut side walls, is one of the characteristic phenomena of the abrasive water jet (AWJ) cutting. The taper represents a serious problem in shape cutting, especially in corners and curvatures. However, deviation of the side walls occurs even in the straight line parts of trajectories. Some differences from character typical for metal cutting have been noticed when studying the rock materials. This article is aimed at the experimental research of the cut walls taper on several rock materials with different genesis and composition. The topic of this contribution to the common knowledge is pointing out the most important differences compared to previous research made mainly on metals. The widths of slots made in plan-parallel plates of rock materials were measured both on the top and on the bottom. The difference between these widths has been used for evaluation of the taper—the angle of the cut walls inclination. The results were compared with the regression equation obtained from experimental results on metals and presented in past. The discrepancy between new findings and previously determined equation is discussed and the most probable explanations are submitted.