• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1845-1850
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• 2004

The laminar impinging jet flow fields were investigated with or without magnetic fields. The transient phenomenon from steady to unsteady flow was founded at specific Reynolds number ranges. In unsteady flow region, the magnetic fields make flow stable. So the characteristics of fluid flow at impingement wall are changed

• 대한기계학회논문집B
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• 제35권8호
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• pp.831-838
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• 2011

마이크로채널 표면의 핵에서 생성된 기포는 물을 작동유체로 이용하는 경우 채널의 좁은 단면적에 의해 압착되어 유동불안정성을 유발한다. 직관 마이크로채널에서 압착된 기포는 관성 유동의 역방향인 채널 상류로 진행한다. 마이크로채널에서 역방향 유동을 없애기 위해 채널 하류의 단면적을 확장시키는 것이 효과적이다. 그 이유는 압착된 기포의 전후단 계면의 표면장력에 의한 압력차이가 계면의 반지름에 역비례해서 자연적으로 기포가 채널 하류로 이동하려는 힘이 발생하기 때문이다. 확장 증발 마이크로채널에서 정적 유동불안정성 모델이 제시되었으며, 실험으로 모델을 검증하였다. 또한, 안정된 확장 시스템을 설계하기 위해 국부 설계 개념을 도입하였다. 검증된 모델과 개념을 바탕으로 안정된 확장 증발 마이크로채널 설계를 성공적으로 수행하였다.

• 한국추진공학회지
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• 제4권2호
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• pp.6-11
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• 2000

고압의 불활성 기체를 이용하여 엔진에 추진제를 공급하는 액체로켓의 경우, 추진제 탱크의 압력은 정상연소상태의 연소압을 기준으로 하여 설계한다. 그러나 연소초기의 연소실 압력은 대기압 상태이므로 과도한 유량이 공급되어 이로 인해 hard-start가 발생하며, 최악의 경우 엔진의 파손을 가져온다. 본 연구에서는 이러한 문제를 해결하고 안정된 연소를 위하여 개선된 추진제 공급시스템을 제안하며, 이는 실제 연소실험을 통해 그 성능을 규명하였다. 이 공급시스템은 연소초기의 급격한 연소실압의 상승을 막기 위하여 추진제를 예연소단계와 주연소단계의 2단계로 공급하며, 연소초기 및 연소 중의 일정한 유량공급을 위해 Cavitating Venturi를 사용하는 시스템이다. 설계 유량보다 적은 양의 추진제를 먼저 공급하여 연소압이 일정수준에 달하도록 예연소압을 형성하게 하는 방법이다. 또한, Cavitating Venturi는 오직 공급압에 의해서만 유량이 결정되며, 출구 압에 영향을 받지 않으므로 연소초기는 물론이고, 연소 중 이상연소에 의해 연소압이 떨어져도 설계치 이상의 유량이 공급되지 않는다.

• 한국연소학회지
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• 제7권1호
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• pp.37-43
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• 2002

Spray characteristics in the swirling flow were investigated by Stereoscopic PIV. Spatial spray structures were measured by PIV as well as PDA in order to understand stable flame stabilization. The feasibility study of Stereoscopic PIV in spray flame was also demonstrated. The size and location of recirculation flow were measured. The stereoscopic PIV could provide 3-D flow fluctuation that cannot be measured by convectional measurement systems.

• 한국수소및신에너지학회논문집
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• 제25권2호
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• pp.191-199
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• 2014

Effects of design variables on the performance of a double-inlet centrifugal blower have been analyzed based on the three-dimensional flow analysis. Two design variables, blade inlet and outlet angles, are introduced to enhance a blower performance. General analysis code, ANSYS-CFX13, is employed to analyze internal flow and a blower performance. SST turbulence model is employed to estimate the eddy viscosity. Throughout the shape optimization of an impeller at the design flow condition, the blower efficiency and pressure are successfully increased by 4.7 and 1.02 percent compared to reference one. It is noted that separated flow observed near cut-off region can be reduced by optimal design of blade angles, which results in stable flow pattern in the blade passage and increase of a blower performance. The stable flow at the impeller also makes good effects at the outlet of a volute casing.

• 대한기계학회논문집
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• 제19권5호
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• pp.1300-1307
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• 1995

The effect of thermal stratification on the turbulent dispersion from a fine cylindrical heat source was experimentally examined in a wind tunnel with and without a strong temperature gradient. A 0.5 mm dia. nichrome wire was used as a line heat source. Turbulent intensities, r.m.s. value of temperature and convective heat fluxes were measured by using a hot-wire and cold-wire combination probe. The results show that the peack value and the spread of the vertical turbulent intensity for the stratified case are far lower than those in the neutral case, which indicates that the stable temperature gradient suppresses the vertical velocity component. All of the third order moments including heat fluxes measured in the stable condition have very small values than those of the neutral case. This nature suggests that the decrease of scalar fluctuations in the stably stratified flow is mainly due to the suppression ofthe turbulent diffusion processes by the stable stratification. A simple gradient model with a composite timescale which has a simple weighted algebraic mean between dynamic and thermal time scale yields reasonably good numerical values in comparison with the experimental data.

• 충청수학회지
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• 제5권1호
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• pp.65-74
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• 1992

In this note, we show that the ${\omega}$-limit mapping is continuous and the Lipschitz constants vary continuously if the flow (x, ${\pi}$) is Lipschitz stable. Moreover we analyse the ${\omega}$-limit sets under the generalized locally Lipschitz stable flows.

• 대한조선학회논문집
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• 제45권1호
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• pp.10-17
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• 2008

In this paper an accurate and stable gridless method that can be applied to multi-dimensional convection problems is developed on a flow directional local grid. A two dimensional pure convection problem is calculated and more accurate and stable solution is obtained compared with other schemes in grid method. The tested numerical schemes include 1st-order upwind scheme, 2nd-order Leith scheme, 3rd-order MUSCL, and QUICK scheme. It is seen that more accurate results are expected when the schemes combined with a MMT control limiter.

• 대한기계학회논문집A
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• 제28권8호
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• pp.1190-1195
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• 2004

A novel manipulation of microfluid width in a microchannel was presented by controlling inflation of a gas boundary. The gas boundary was formed by heating water with a microheater in a semicircular shape from a chamber which was connected symmetrically to the microchannel. The formed gas boundary inflated perpendicularly to the flow direction and, consequently, the microfluid width was narrowed. The inflation and contraction were flexibly like a virtual wall and dependent on two factors: one is the flow velocity of the microfluid and the other is the pressure inside the gas boundary. Dimensions of the chamber and the microchannel width were determined empirically as same of $300\;{\mu}m$ for stable operation. The width of microfluid was manipulated manually with the microheater and could be maintained as up to $22\;{\mu}m$. The stable focusing began to be distorted when the flow velocity exceeded 17.8 mm/s.

• 한국압력기기공학회 논문집
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• 제8권2호
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• pp.42-47
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• 2012

The containment local leakage rate testing in nuclear power plants is performed in accordance with ANSI/ANS 56.8-1994 in Korea. Two methods, the make-up flow rate and the pressure decay, are used for local leakage rate testing. Though ANSI/ANS 56.8-1994 does not define clearly the minimum test duration for the make-up flow rate method, it requires obtaining the data after reaching the stable condition. Thus the prerequisite stable condition for data acquisition and the testing time is differently applied to each NPPs. Therefore, this study presents a standardized test procedure for data stabilization and testing time through experiments to improve the test reliability.