• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3150-3155
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• 2007

This paper describes an experimental work to investigate the effect of mesh screen device on the jet structure and acoustic characteristics of over-expanded supersonic jet. The mesh screen device is placed into the supersonic jet stream. In order to perturb mainly the initial jet shear layer, the hole is perforated in the central part of the mesh screen. The diameter of the perforated hole and the location of mesh screen device are varied. A Schlieren optical system is used to visualize the flow fields of supersonic jet without and with the mesh screen device. Pitot pressure measurement is carried out to obtain the pressure distribution in the jet flow. Acoustic measurement also is performed to obtain the OASPL and noise spectra. The results obtained show that the jet structure and the jet noise control effectiveness is strongly dependent upon the diameter of the perforated hole and the location of the mesh screen device in the jet stream. Provided that the mesh screen device is placed at the location to perturb effectively the initial shear layer, the present control method is effective in suppressing the supersonic jet noise.

• Nuclear Engineering and Technology
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• v.55 no.7
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• pp.2498-2503
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• 2023

When the reactor vessel is penetrated in a severe accident of light water reactor, the molten fuel-coolant interaction including the jet breakup occurs and the jet breakup length becomes one of the important parameters. Most numerical studies on jet breakup process have been carried out using dedicated computer codes. Some researchers are trying to apply commercial CFD codes to their investigations on comprehensive jet breakup process. However, the complexity of the phenomena limits the CFD application only to hydrodynamic aspects. In the present study, numerical analysis of jet breakup under vapor generation is pursued using the STAR-CCM + code. The obtained CFD prediction of the MATE09 experiment shows jet breakup progression patterns consistent to the images taken in the experiment. Further, the predicted positions of leading head, which determine the jet breakup length, are in good agreement with the MATE 09 data. The investigation of hydrodynamic effects on the jet breakup with higher jet velocity results in a stronger shear force and earlier jet breakup process even though there exists the vapor pocket around the corium jet. In future studies, the effect of vapor intensity on the jet breakup length would be investigated further by changing other parameters.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.125-129
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• 2005

Flow control has been performed using synthetic jet on NACA23012. In order to improve aerodynamic performance, synthetic jet is located near separation paint on airfoil with leading edge droop and plain flap. The flow control using synthetic jet shows that stall characteristics and control surface performance can be improved through resizing separation vortices. Stall is delayed and stall characteristics are improved when synthetic jet is applied from separation region of leading edge droop. Control surface effectiveness is increased and lift is increased when synthetic jet applied at the flap leading edge region. The results show that aerodynamic characteristics can be improved through leading edge droop with synthetic jet at near separation and plain flap with synthetic jet at the flap leading edge. The combination of synthetic jet and simple high lift device is as good as fowler flap system.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.1
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• pp.213-221
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• 1998

The investigation regarding the ignition system of a plasma jet explored by using a constant volume vessel. The purpose of this study is to elucidate relation between the characteristics of the configuration and jet ejection of plasma jet plug, when the sub energy were supplied at plasma jet ignition system. From the results of a visualization by the schlieren system, the jut ejection for plasma jet ignition are depended on the jet plug configuration and sub energy, but the configuration of plasma jet plug is more influenced than the sub energy on the plasma jet ejection. And the plasma jet ignition strongly influences upon the combustion enhancement than the conventional spark ignition.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1717-1723
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• 2003

Experimental study is conducted to investigate the cooling performance of impinging jet from microtube using Joule-Thomson effect to apply practical applications. And also the heat transfer characteristics of a impinging jet itself and the impinging jet with Joule-Thomson effect are tested to make a comparative study of the two different general ideas. For this propose, two kinds of copper microtubes which have 200 tim and 300 tim in inner diameter respectively were tested and $N_2$ was used as a working fluid. In case of impinging jet without Joule-Thomson effect, heat transfer coefficients distributions were similar to those of normal impinging jet. But in impinging jet with Joule-Thomson effect, the heat transfer coefficients decrease as jet-to-surface increases contrary to the case of the normal jet. As a result, much higher heat transfer coefficients are obtained with Joule-Thomson effect than those of the normal jet without J-T effect.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.84.2-84.2
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• 2011

Astrophysical jets play important roles in many interesting astronomical phenomena, such as star formation, gamma-ray bursts, and active galactic nuclei. The jets are thought to be driven by rotating disks through magneto-centrifugal processes. However, quantitative understanding of the jet-driving mechanism has been difficult because examples showing rotation in both disk and jet are rare. One of the important quantities in the models of jet engine is the size of the jet-launching region. The bipolar jet of the NGC 1333 IRAS 4A2 protostar shows a lateral velocity gradient, which suggests that the SiO jet is rotating around its axis. The jet rotation is consistent with the rotation of the accretion disk. The disk-jet rotation kinematics suggests that the jet-launching region on the disk, or the outflow foot-ring, has a radius of about 2 AU, which supports the disk-wind models.

• Journal of the Korean Physical Society
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• v.73 no.9
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• pp.1230-1239
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• 2018

We derive a factorization theorem for the jet mass distribution with a given $p^J_T$ for the inclusive production, where $p^J_T$ is a large jet transverse momentum. Considering the small jet radius limit ($R{\ll}1$), we factorize the scattering cross section into a partonic cross section, the fragmentation function to a jet, and the jet mass distribution function. The decoupled jet mass distributions for quark and gluon jets are well-normalized and scale invariant, and they can be extracted from the ratio of two scattering cross sections such as $d{\sigma}/(dp^J_TdM^2_J)$ and $d{\sigma}/dp^J_T $. When $M_J{\sim}p^J_TR$, the perturbative series expansion for the jet mass distributions works well. As the jet mass becomes small, large logarithms of $M_J/(p^J_TR)$ appear, and they can be systematically resummed through a more refined factorization theorem for the jet mass distribution.

• Journal of the Korean Society of Visualization
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• v.16 no.3
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• pp.16-25
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• 2018

PIV experiments were carried out to visualize the velocity distribution of the sweeping jet impinging onto a flat plate and kinematic behavior of the jet from the fluidic oscillator. Two parameters such as four different Re cases and four different jet-to-wall distances were examined. Time-resolved two dimensional PIV measurements were performed for both streamwise and normal planes respect to the jet axis. Ensemble averaged and phase averaged velocity fields were obtained for the tested range of parameters. The sweeping frequency of the jet increases linearly with increase of Re. The kinetic energy of the sweeping jet decreases as the distance from the jet to the impinging plate increases. In addition, turbulence flow is generated due to the swinging motion of sweeping jet, and various vortices such as primary and secondary vortex are observed near the impinging wall.

• Journal of Korea Water Resources Association
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• v.30 no.5
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• pp.467-475
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• 1997

In this study, breakwater model which has several outlet pipes to discharge heated water is settled in the experimental open channel and velocity distribution of wall jet is measured. Numerical simulation of velocity structure of wall jet using 3-dimensional computer model. Fluent model, is also carried out. The calculated results are verified with the experimental results and the flow characteristics of wall jet are investigated. The length of zone of flow establishment of wall jet is shorter than that of free jet, and the diminution rate of jet centerline longitudinal velocity is larger than that of free jet. Characteristics of buoyant jet and non-buoyant simple jet simulated by Fluent model are compared. Near the outlet pipe, in the region where x/lQ is over 15, this is reversed. Comparison of vertical distribution of longitudinal velocity shows that positive velocity of non-buoyant jet is bigger than that of buoyant jet in the bottom layer and in the upper layer, negative velocity of non-buoyant jet is bigger too. Flow separation in free surface of the buoyant jet occurs in smaller distances from the outlet than the non-buoyant jet. Buoyant jet expands faster than the non-buoyant jet in vertical direction.

• 한국연소학회:학술대회논문집
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• 2004.06a
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• pp.49-56
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• 2004

A two-dimensional twin-jet counterflow system has been designed, in which two streams from two double-slit nozzles form a counterflow. This flow system enables one to systematically investigate various effects on non-premixed flames, including the non-premixed flame interaction, the edge flame behavior and the effect of curvature. Non-premixed flame interaction in the twin-jet counterflow system has been investigated numerically for methane fuel diluted with nitrogen. Three types of non-premixed flame(conventional counterflow flame, crossed twin-jet flame and petal shaped flame) were simulated depending on the combination of fuel/oxidizer supply to each nozzle. The extinction characteristics of non premixed methane flame in the twin-jet counterflow have been investigated numerically. The boundary of the existence of petal-shaped flames was identified for the twin-jet counterflow flames. Due to the existence of the unique petal-shaped flames, the extinction boundary for the twin-jet counterflow can be extended significantly compared to that for the conventional counterflow non-premixed flames, through the interaction of two flames. Through the comparison of the crossed twin-jet flame and the conventional counterflow flame, structure of the crossed twin-jet counterflow flame is analysed. Through the comparison of the petal shaped flame and the conventional counterflow flame, the extension of the extinction boundary for the twin-jet counterflow is investigated.