• Journal of Advanced Marine Engineering and Technology
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• 제21권1호
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• pp.43-48
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• 1997

본 연구에서는 미분탄과 공기를 혼합하여 노즐을 통하여 바닥면에 캐비티가 존재한 사각단면 분류층 연소실로 분사 시킬 때에 분사된 혼합유동의 평균속도,농도 및 난류특성치들의 유체역학적 거동을 3차원 측정이 가능한 PDA를 이용하여 실험적으로 규명하였다. 바닥면의 재부착점은 X/D=15인 부근에서 나타나며, 재부착점 이후에서 부터 각 단면의 상사성이 이루어지는 것으로 나타났다. 사각 연소실 바닥면 관통의 영향을 받아 난류강도와 난류전단용력의 최대값은 중심축보다 높은 Y/D=6인 점에서 최대가 되며, 미분탄의 농도는 Y/D=6~8인 점에서 최대값이 나타났다.

• 한국자동차공학회논문집
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• 제2권1호
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• pp.38-50
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• 1994

To improve the efficiency of internal combustion engines, it is necessary to understand mixed air-fuel in-cylinder flow processes accurately at intake and compression strokes. There is experimental and numerical methods to analyse in-cylinder flow process. In numerical method, standard $k-{\varepsilon}$ model with wall function was mostly adopted in in-cylinder flow process. But this type model was not efficiently predicted in the near wall region. Therefore in the present study, low Reynolds number $k-{\varepsilon}$ model was adopted near the cylinder wall and standard $k-{\varepsilon}$ model in other region. Also QUICK scheme was used for convective difference scheme. This study takes axisymmetric reciprocating model engine motored at 200rpm with a centrally located valve, incorporated 60 degree seat angie, and flat piston surface excluding inlet port. Because in-cylinder flow processes are undergoing unsteady and compressible, averaged cylinder pressure and inlet velocity at arbitrary crank angle are determined from thermodynamic analytic method and incylinder states at that crank angle are iteratively determined from the numerical analytic method.

• 대한기계학회논문집
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• 제18권4호
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• pp.912-919
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• 1994

The engine combustion is one of the most important processes affecting performance and emissions. One effective way to improve the engine combustion is to control the motion of the charge inside a cylinder by means of optimum induction system design, because the flame speed is mainly determined by the turbulence at compression(TDC) process in S.I. engine. It is believed that the tumble and swirl motion generated during intake stroke breaks down into small-scale turbulence in the compression stroke of the cycle. However, the exact nature of this relationship is not well known. This paper describes the tumble flow measurements inside the cylinder of a 4-valve S.I. engine using laser Doppler velocimetry(LDV) under motoring(non-firing) conditions. This is conducted on an optically assesed single cylinder research engine under motored conditions at an engine speed of 1000rpm. Three different cylinder head intake port configurations are studied to develop a better understanding the tumble flow generation, development, and breakdown mechanisms.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.135-138
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• 2007

액체추진제 추력기에 사용되는 인젝터 분무액적의 2차원 공간분포 특성을 이중모드 위상도플러속도계(dual-mode phase Doppler anemometry, DPDA) 기법을 적용하여 고찰하였다. 분무액적의 속도, 난류강도, Sauter 평균직경(Sauter mean diameter, SMD), 수밀도, 그리고 체적플럭스 등의 분무분열특성 매개변수 변이를 정량화 하여 인젝터 분무의 거시적 거동을 규명한다. 본 연구는 추력기의 성능특성 이해는 물론 새로운 추력기의 설계기반 구축에 기여할 수 있을 것이다.

• Journal of Advanced Marine Engineering and Technology
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• 제28권4호
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• pp.624-631
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• 2004

The experimental study on heat transfer characteristics of protruding heated block array as conducted to investigate and to compare the performance of impinging single circular jet in fully developed tube with a twisted tape as a swirl generator. The effects of jet Reynolds number(Re=8700, 13800, 20000. 26500), dimensionless jet-to-block distance(H/d=1. 3, 5. 7) and swirl number(S=0.11, 0.23, 0.30) of the swirl jet on the average Nusselt number for each block and all blocks have been examined. Measurements of heat transfer rate on block surfaces were used naphthalene sublimation technique. Mean velocity and turbulence intensity of the jet along the axis were measured. Potential core length of the jet was 5 times of nozzle diameter because it was fully developed and initially turbulent. With the twisted tape in the nozzle, heat transfer coefficients were higher than those without the twisted tape. which are mainly caused with increasing the jet Reynolds number and swirl number.

• 대한기계학회논문집B
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• 제24권12호
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• pp.1670-1677
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• 2000

An experimental investigation on heat transfer characteristics of two-dimensional heated blocks using a confined impinging slot jet has been performed. The effect of jet Reynolds number(Re=3900, 5800, 9700), streamwise block spacing(p/w=0.5, 1, 1.5) and dimensionless nozzle to block distance(H/B=1, 2, 4, 6) have been examined with five isothermally heated blocks. With the measurement of jet mean velocity and turbulence intensity distributions at nozzle exit, initially turbulent regimes, are classified. To clarify local heat transfer characteristics, naphthalene sublimation technique as used. The maximum Nusselt number at the stagnation point for the jet Reynolds number is occurred at H/B=4. Besides, the local and a average heat transfer of heated blocks increase with decreasing streamwise block spacing and increasing jet Reynolds number.

• 대한기계학회논문집B
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• 제25권12호
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• pp.1802-1812
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• 2001

The purpose of this study is to analyze numerically the movement of particles included in turbulent fluid flow characteristics of metallic surfaces. To describe fluid flew, the incompressible Navier-Stokes equation discretized by the finite volume method were solved on the non-orthogonal coordinates with non-staggered variable arrangement, and the k-$\xi$ turbulence model was adapted. After fluid flow was calculated, particle movement was predicted from the Lagrangian approaches. Non-essential complexities were avoided by assuming that the particles had spherical shapes and the Stoke's drag formula only consisted of external farces acting upon them. In order to validate the numerical calculations, the results were compared with the experimental data reported in literature and agreed well with them. The drag force coefficient equation showed better agreement with the experimental data in the prediction of particle movement than the correction factor equation. Impact velocity and impact angle increased as inlet turbulence intensity decreased, relative jet height was lower. or the Reynolds number was larger.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.610-614
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• 1996

Sealing of lubricat-air mixture in the high performance machining conte is one of most the important characteristics to carry out enhanced lubrication. High speed spindle requires non-contact type of sealing mechanism. Evaluating an optimum seal design to minimize leakage is concerned in the aspect of flow control. Effect of geometry and leakage path are evaluated according to variation of sealing geometry, Velocity, pressure, turbulence intensity of profile is calculated to fina more efficient geometry and variables. This offers a methodological way of enhancement seal design for high speed spindle. The working fluid is regarded as two phases that are mixed flow of oil phase and air phase. It is more reasonable to simulate an oil jet or oil mist type high speed spindle lubrication. Turbulence and compressible flow model are used to evaluate a flow characteristic, This paper arranges a geometry of mostly used non-contact type seal and analyzes leakage characteristics to minimize a leakage on the same sealing area.

• 대한기계학회논문집
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• 제12권1호
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• pp.116-122
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• 1988

본 연구에서는 공기와 물을 매질로 사용하여 3차원 계면파가 존재하는 근사수평 반류성층유동에서의 계면전단응력과 마찰계수를 결정하였다. 기상과 액상의 유량조건에 따라 3차원 계면파의 특성을 needle contact법에 의하여 측정 하였으며, 기상의 압력강하와 속도분포를 구하여 계면전단응력을 구하였다. 또 공학적인 응용을 위하여 3차원과 영역에서의 계면마찰계수에 관한 실험식을 개발하였다. 그리고 거칠은 고체표면에서의 마찰계수를 표현한 Nikuradse식을 이용하여 계면의 등가조도(equivalent roughness)를 계산하였으며 이것을 계면의 파고교란강도와 비교분석하여 계면전단응력에 영향을 미치는 인자들을 규명하였다.

• 대한조선학회논문집
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• 제29권4호
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• pp.132-145
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• 1992

추진 효율 향상을 위한 대칭형 전류 고정날개-프로펠러 추진시스템의 설계, 이론성능해석 및 모형시험 과정을 정리하였다. 프로펠러 후류에서의 회전방향 운동에너지 회수를 통한 추진효율 향상을 도모하기 위하여 프로펠러 전방에 반대방향의 회전 속도를 주기 위한 고정날개를 설치하였다. 모형시험 결과 대칭형 전류 고정날개 추진시스템이 단독프로펠러에 비하여 3%정도 추진효율의 향상이 있음을 확인하였다. 실선 장착시에는 선체 반류에서의 난류 강도증가 및 레이놀드수 증가에 따른 고정날개 표면에서의 박리현상 감소에 의하여 고정날개 항력계수가 감소할 것으로 추정되며 그에 따라 본 추진시스템의 추진효율 증가량이 더욱 커지리라 판단된다.