• 한국유체기계학회 논문집
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• 제6권3호
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• pp.21-27
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• 2003

Dispersion of coolant jets in a film cooling flow field is the result of a highly complex interaction between the film cooling jets and the mainstream. In order to investigate the effect of blowing ratios on the film cooling of a turbine blade, cylindrical body model is used. Mainstream Reynolds number based on the cylinder diameter is $7.1{\times}10^4$. The effects of coolant flow rates are studied for blowing ratios of 0.7, 1.0, 1.3 and 1.7, respectively. The temperature distribution of the cylindrical model surface is visualized with infrared thermography (IRT). Results show that the film cooling performance could be significantly improved by the shaped injection holes. For higher blowing ratio, the spanwise-diffused injection holes are better due to the lower momentum flux away from the wall plane at the hole exit.

• 대한기계학회논문집B
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• 제22권4호
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• pp.499-509
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• 1998

In the absorption process of water vapor in a liquid film, the composition of the gas phase, in which a non-absorbable gas is combined with the absorbate influences the transport characteristics remarkably. In the present study, the absorption processes of water vapor into aqueous solution of lithium bromide in the presence of non-absorbable gases were investigated analytically. The continuity, momentum, energy and diffusion equations for the solution film and gas phase were formulated in integral forms and solved numerically. It was found that the mass transfer resistance in gas phase increased with the concentration of non-absorbable gas. However the primary resistance to mass transfer was in the liquid phase. As the concentration of non-absorbable gas in the absorbate increased, the liquid-vapor interfacial temperature and concentration of absorbate in solution decreased, which resulted in the reduction of absorption rate. The reduction of mass transfer rate was found to be significant for the addition of a small amount of non-absorbable gas to the pure vapor, especially at the outlet of an absorber where non-absorbable gases accumulated. At higher non-absorbable gas concentration, the decrease of absorption flux was almost linear to the volumetric concentration of non-absorbable gas.

• 대한기계학회논문집B
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• 제28권9호
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• pp.1093-1100
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• 2004

Numerical analysis of the heat transfer associated with droplet impact on a hot solid surface is performed by solving the equations governing conservation of mass, momentum and energy in the liquid and gas phases. The deformed droplet shape is tracked by a level set method which is modified to achieve volume conservation and to include the effect of contact angle at the wall. The numerical method is validated through the calculations for the cases reported in the literature. Based on the numerical results, the heat transfer rate is found to depend strongly on the droplet spread radius. Decreased advancing/receding contact angles enlarge the splat radius and in turn enhance the wall heat flux. The effect of impact velocity on the droplet spread is reduced as the droplet size decreases. Also, droplet atomization is observed to significantly enhance the heat transfer rate and the effect is pronounced for a smaller size of droplet. An existing model equation to predict the maximum spread radius is improved for application to a micro droplet.

• 대한기계학회논문집B
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• 제27권7호
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• pp.883-892
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• 2003

The experiment using three-dimensional laser Dopperr velocimetery (LDV) measurements and the computation using the Reynolds stress model of the commercial code, FLUENT, were conducted to give a clear understanding on the structure of tip leakage flow in a forward-swept axial-flow fan operating at the maximum efficiency condition. The tip leakage vortex was generated near the position of the minimum wall static pressure, which was located at approximately 12% chord downstream from the leading edge of blade suction side, and developed along the centerline of the pressure trough within the blade passages. A reverse flow between the blade tip region and the casing, induced by tip leakage vortex, acted as a blockage on the through-flow. As a result, high momentum flux was observed below the tip leakage vortex. As the tip leakage vortex proceeded to the aft part of the blade passage, the strength of tip leakage vortex decreased due to the strong interaction with the through-flow and casing boundary layer, and the diffusion of tip leakage vortex caused by high turbulence. In comparison with LDV measurement data, the computed results predicted the complex viscous flow patterns inside the tip region, including the locus of tip leakage vortex center, in a reliable level.

• Ocean and Polar Research
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• 제34권3호
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• pp.287-296
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• 2012

In the theory of source-driven abyssal circulation, the forcing is usually assumed to be steady source (deep-water formation). In many cases, however, the deep-water formation occurs instantaneously and it is not clear whether the theory can be applied well in this case. An attempt is made to resolve this problem by using a simple reduced gravity model. The model basin has large depth change compared for its size, like the East Sea, such that isobaths nearly coincide with geostrophic contours. Deep-water is formed every year impulsively and flows into the model basin through the boundary. It is found that the circulation driven by the impulsive source is generally the same as that driven by a steady source except that the former has a seasonal fluctuation associated with unsteadiness of forcing. The magnitudes of both the annual average and seasonal fluctuations increase with the rate of deep-water formation. The problem can be approximated to that of linear diffusion of momentum with boundary flux, which well demonstrates the essential feature of abyssal circulation spun-up by periodic impulsive source. Although the model greatly idealizes the real situation, it suggests that abyssal circulation can be driven by a periodic impulsive source in the East Sea.

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권4호
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• pp.286-292
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• 2011

In order to design a shear coaxial injector of solid particles for underwater propulsion system, basic experiments on gas-liquid shear coaxial injector are necessary. In the gas-liquid coaxial injector self-pulsation usually occurs with an intense scream. When self-pulsation occurs, mass flow rate oscillation and intense scream are detected by the interactions between the liquid and gas phase. Self-pulsation must be suppressed since this oscillation may cause combustion instabilities. Considerable research has been conducted on self-pulsation characteristics, but these researches are conducted in swirl coaxial injector. The main objective of this research is to understand the characteristics of self-pulsation in shear coaxial injector and reveal the mechanism of the phenomenon. Toward this object, self-pulsation frequency and spray patterns are measured by laser diagnostics and indirect photography. The self-pulsation characteristics of shear coaxial injector are studied with various injection conditions, such as the pressure drop of liquid and gas phase, and recess ratio. It was found that the frequency of the self-pulsation is proportional to the liquid and gas Reynolds number, and proportional to the L/d.

• 대한조선학회논문집
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• 제47권2호
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• pp.178-187
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• 2010

The performance of the waterjet system of a patrol boat has been experimentally studied. A waterjet propulsion system has many advantages comparing with a conventional screw propeller especially for high speed craft because of its good cavitation performance. This paper describes experimental procedure and analysis method of self-propulsion tests with a 1/12-scale model. Experimental results were analyzed according to ITTC 96 standard method. The full-scale effective power and delivered power of the ship were also analyzed and the full-scale speed predicted from the model test compares reasonably with the measured full-scale results of the sea trial.

• 한국추진공학회지
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• 제14권2호
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• pp.1-9
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• 2010

난류 유동장으로 분사되는 액체 제트의 액주 분열과 액적 미립화 현상에 관한 LES를 수행하였다. 기체상태의 공기 유동해석에 Eulerian 해법을 사용하고, 액적 추적을 위하여 Lagrangian 해법을 사용하여 기체-액체간 이상유동(two phase flow) 해석을 수행하였다. 액적 분열 과정 모사에 blob-KH 분열 모델을 적용하여 액주와 액적의 분열이 관찰되었다. 일정한 공기 유동 조건에서 액체 분사 속도 변화를 통한 액체-기체 운동량 플럭스 비의 변화에 따른 액체 제트의 침투깊이를 조사하였으며 실험결과와 유사함을 알 수 있었다. 분사 제트의 분열에 따라 유동장에 존재하는 액적의 분포를 Sauter 평균 입경(SMD)의 분석을 통해 수행하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 B
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• pp.972-974
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• 2005

The present work deals with the theoretical study of the effects of copper vapours resulting from the erosion of the electrodes on the properties of a SF6 arc in a Laval nozzle. Computations have been done for a DC arc of 1000A with upstream gas pressure of 3.75MPa. The arc plasma is assumed to be in local thermodynamic equilibrium(LTE). The sheath and non-equilibrium region around the electrodes are not considered in this model. However, its effects on the energy flux into the electrodes are estimated from some experimental and theoretical data. The turbulence effects are calculated using the Prandtl mixing length model. A conservation equation for the copper vapour concentration is solved together with the governing equations for mass, momentum and energy of the gas mixture. Comparisons were made between the results with and without electrodes erosion. It has been found that the presence of copper vapours cools down the arc temperature due to the combined effects of increased radiation and increased electrical conductivity. The copper vapour distribution is very sensitive to the turbulent parameter. The erosion of upstream electrode(cathode) has larger effects on the arc compared to the downstream electrode(anode) as the copper vapour eroded from the anode cannot diffuse against the high-speed axial flow.

• 한국추진공학회지
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• 제23권4호
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• pp.10-20
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• 2019

충격파 개념을 이용하는 유체 추력벡터 제어는 빠른 벡터링 응답, 간단한 구조 및 낮은 무게로 인하여 큰 벡터링 성능을 달성하는데 많은 이점을 제공한다. 본 논문에서는 전산유체역학 기법을 사용하여 슬롯 인젝터를 가진 3차원 직사각형 초음속 노즐에 대하여 연구를 수행하였다. 계산 방법론을 검증하기 위하여 수치 결과를 실험 데이터로 비교하였다. 대칭 평면에서의 상부 및 하부 노즐벽을 따르는 압력분포는 시험 결과와 잘 일치하였다. $k-{\omega}$ SST 난류모델을 기반으로 한 수치해석을 통하여, 운동량 플럭스 비율의 영향을 철저히 조사하여 추력의 성능 변화를 명확하게 나타내었다.