• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.5
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• pp.526-531
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• 2001

The flow of remote field eddy current energy is studied at nonmagnetic coaxial tubes by using both experiments and finite element calculations based on commercial software package. The results showed that remote field eddy current energy at coaxial tubes flow along over the outer surface of external tube, not through the gap between internal and external tubes. This means that the through wall transmission characteristic of remote field eddy current testing (RFECT) is still valid at tube in tube configurations and the RFECT could be potential nondestructive technique for crack detection, spacer location and gap sizing at the coaxial CANDU fuel channel tubes.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.2
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• pp.147-155
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• 2001

Experimental investigations were conducted for two hydrogen-nitrogen coaxial jet diffusion flames. A flame was a conventional coaxial jet diffusion flame and the other was a coaxial jet diffusion flame of which ambient air-jet turbulence was intensified. In this study, firstly two kinds of NOx measuring system were campared by using different convertors, secondly the NOx formation characteristics were investigated in order to examine the effect of turbulence intensity. In this study it is known that stainless convertor has some problem in the converting process from NO$_2$to NO in fuel rich region but molybdenum convertor can detect the amount of NOx correctly. The increase of turbulence intensity reduces the thermal NOx less than a half in our experiment and this effect is conspicuous near the nozzle. The conversion rate from NO to NO$_2$and the portion of NO$_2$among NOx are increased with turbulence intensity. These NOx measurements will help to understand the influences of turbulence intensity on NOx formation.

• Journal of the Korean Society of Combustion
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• v.5 no.2
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• pp.51-62
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• 2000

The relationship among the flame radiation, NOx emissions, residence time, and global strain rate are examined for turbulent non-premixed jet flames with wide variations in coaxial air conditions. Measurements of NOx emission, flame geometry and flame radiation were made to explain the NOx emission scaling based on global parameters such as flame residence time, global strain rate, and radiant fraction. The overall 1/2-power scaling is observed in coaxial air flames, irrespective of coaxial air conditions, but the degree of deviation from the 1/2-slope curve in each case differs from one another. From the comparison between the results of pure hydrogen flames and those of helium diluted hydrogen flames, it is observed that flame radiation plays a significant role in pure hydrogen flames with coaxial air and the deviation from 1/2-power scaling may be explained in two reasons: the difference in the flame radiation and the difference in jet similarity in coaxial air flames. From the radiation measurements, more detailed explanations on these deviations were suggested.

• Journal of ILASS-Korea
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• v.22 no.2
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• pp.62-68
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• 2017

It is important to study on the combustion instability to develop liquid rocket engines for preventing lower combustion efficiency and destruction of combustion chamber. There are many researches on simplex injector with liquid pulsation to solve this problem. In real rocket engine system, however, they use coaxial injectors. Therefore, research on coaxial injector with liquid pulsation is essential. In this study, we investigate dynamic characteristics of gas centered swirl coaxial injector varying tangential inlet diameter. A mechanical pulsator was used to generate an excitation in the liquid flow, and the response characteristics of the injector were confirmed. As tangential inlet diameter increased, mass flow rates increased and spray angle decreased. As tangential inlet diamter decreased, gain decreased because the pressure fluctuation in the injector manifold rarely passed through the inlet. Additionally, it was confirmed that a sufficiently small tangential inlet served as a damper.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.4
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• pp.94-101
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• 2001

The shock structure of dual coaxial jet is experimentally investigated. Eight different kinds of coaxial, dual nozzles are employed to observe the major features of the near field shock structure on the supersonic, coaxial, dual jets. Four convergent-divergent supersonic nozzles having the Mach number 2.0 and 3.0 are used to compare the coaxial jet flows discharging from two sonic nozzles. The primary pressure ratio is changed in the range between 1.0 and 10.0, and the assistant jet ratio from 1.0 to 4.0. The results show that the impinging angle, nozzle geometry and pressure ratio significantly affect the near field shock structure, Mach disk location and Mach disk diameter.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.228-233
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• 2004

The spray and acoustic characteristics by the self-oscillation of a swirl coaxial injector were experimentally studied. The self-oscillation of a swirl coaxial injector is defined as pressure and flowrate oscillations by a time-delayed feedback between liquid and gas phase and has strong influences on atomization and mixing processes. Hence the occurrence and effect of the self-oscillation are measured using shadow photography technique, acoustic test and PDPA. The occurrence of self-oscillation largely depends on the injection conditions, such as pressure drop of liquid phase and relative momentum ratio. From the experimental results, self-oscillation occurs when the momentum of gas phase is enough large and the smaller the pressure drop of liquid phase is, the better self-oscillation occurs at the same momentum ratio. The self-oscillation is also affected by injector geometries, increasing the recess length results in the expansion of self-oscillation region and the increase of sound pressure level. The self-oscillation of a swirl coaxial injector accompanies a high intensity scream and this scream may provide harmful disturbances to combustion processes. Self-oscillation leads to strong changes in the drop size distribution and smoothly varies the slope of radial SMD distribution.

• Journal of the Korea Institute of Military Science and Technology
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• v.23 no.4
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• pp.311-318
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• 2020

This study investigates the performance and blade airloads for a rigid coaxial rotor of high-speed compound unmanned rotorcrafts. The present compound unmanned rotorcraft uses not only a rigid coaxial rotor, but also wings and propellers for high-speed flights. For the rigid coaxial rotor in this work, CAMRAD II, a rotorcraft comprehensive analysis code, is used to study the performance at a flight speed of up to 250 knots and blade section lift forces at 230 knots. As the flight speed increases, the rotor power decreases; however, the power of propellers increases to overcome the drag force of a rotorcraft in high-speed flight. The effective lift-to-drag ratio of a rotor has the maximum value of about 11.6 which is much higher than the value of the conventional helicopter. The blade section lift forces of the upper and lower rotors at 230 knots show the similar variation trends for one rotor revolution, and the impulses because of the aerodynamic interaction between both rotors are observed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.16-19
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• 2011

An experimental study on the spray characteristics of Gas-centered swirl coaxial injectors(GCSCI) for high-performance staged combustion rocket engines has been carried out using cold flow tests. In this study, water and gaseous nitrogen are used as working fluids and a back-lit photography technique with image processing for the measurements of spray characteristics. Our study is focused on the effect of injector geometries like as gap thickness of liquid nozzle and gas nozzle and momentum flux ratio for fundamental understanding of the injectors.

• Structural Engineering and Mechanics
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• v.16 no.6
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• pp.655-674
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• 2003

Investigated in this study are the natural vibration characteristics of the coaxial cylindrical shells coupled with a fluid. Theoretical method is developed to find the natural frequencies of the shell using the finite Fourier series expansion, and their results are compared with those of finite element method to verify the validation of the method developed. The effect of the fluid-filled annulus and the boundary conditions on the modal characteristics of the coaxial shells is investigated using a finite element modeling.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.153-156
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• 2014

This study was aimed to assess combustion stability for coaxial swirl injector and FOOF impinging injector which would be candidates in liquid rocket engine combustors. Simulating combustion tests under atmospheric condition have been conducted by gaseous oxygen and the mixture of methane and propane, using two actual injectors. By analyzing the measured dynamic pressure signals, we have evaluated the combustion stability margin of both injectors by drawing a stability map.