• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.4
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• pp.42-49
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• 2000

A computation using the mass-averaged implicit Wavier-Stokes equations has been applied to solve the flow fields of the supersonic jets normally injected into supersonic freestreams and several types of turbulence model has been employed to close the governing equations. The ratio of the freestream to injection flow total pressures has been varied to elucidate the major characteristics of the mixing flow of the two streams. The freestream Mach number has been varied to investigate some change in the injection flow field. The results show that the positions of the separation and reattachment, locating upstream and downstream of the injection hole respectively, are strongly dependent on the ratio of total pressures and the freestream Mach number.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.1
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• pp.92-100
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• 2018

Vortical systems are considered a main feature to sustain turbulence in a boundary layer through interaction. Such turbulent structures result in frictional drag and erosion or vibration in engineering applications. Research for controlling turbulent flow has been actively carried out, but in order to show the effect of vortices in a turbulent boundary layer, it is necessary to clarify the mechanism by which turbulent energy is transferred. For this purpose, it is convenient to demonstrate and capture phenomena in a laminar boundary layer. Therefore, in this study, the interactions of disturbed flow around a hemisphere on a flat plate in laminar flow were analyzed. In other words, a street of hairpin vortices was generated following a wake region formed after flow separation occurred over a hemisphere. Necklace vortices surrounding the hemisphere also appeared due to a strong adverse pressure gradient that brought high momentum fluid into the wake region thereby leading to an increase in the frequency of hairpin vortices. To mitigate the effect of these necklace vortices, local suction control was applied through a hole in front of the hemisphere. Flow visualization was recorded to qualitatively determine flow modifications, and hot-film measurements quantitatively supported conclusions on how much the power of the hairpin vortices was reduced by local wall suction.

• Proceedings of the KAIS Fall Conference
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• 2009.12a
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• pp.511-514
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• 2009

현재 일반적으로 사용되는 300cc 소형엔진 기화기의 최적화 및 성능 향상을 위하여 유동해석을 수행하였다. 베르누이의 정리를 기본으로, 성능을 발휘하는 주요 설계인자인 기화기 내부의 벤튜리 튜브의 각도, 길이 등을 변수로 하여 유동해석을 수행하였다. 그 결과를 분석하여 최적화된 모델을 제시하였다. 결론적으로, 유동 해석을 바탕으로 기존 사양 대비 향상된 성능의 모델을 제시하였다. 유동해석을 통해 기화기 내부의 벤튜리관에 곡면(Rounding)처리를 적용함으로 기화기에서 소모되는 흡기저항을 줄여 펌핑로스를 저감활수 있음을 확인하였다. 펌핑로스의 저감은 엔진 연비의 향상과 엔진토크에 긍정적 효과로 작용할 것으로 기대된다. 벤튜리관의 출구 각도를 감소시킴으로 박리를 개선하여 Dead Volume을 줄임으로서 기존 모델에 대비하여 원활해진 유동의 흐름을 얻을 수 있었다. 이는 흡기유량을 증대시키고 엔진출력을 상승시키는 효과로 작용할 것으로 예상된다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.387-392
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• 2006

A small supersonic wind tunnel was designed and built to study the flow characteristics of a supersonic impulse turbine cascade. Experiments are performed to find flow characteristics of supersonic turbine with the cascade positions and to find factor of expansion loss. The supersonic cascade with a 2-dimensional supersonic nozzle was tested with the cascade positions. Firstly, the flow was visualized by Z-type Schlieren system. Finally, highly complicated flow patterns including shocks, nozzle-cascade interaction and shock boundary layer interactions, flow characteristics of the supersonic turbine were observed.

• The Journal of the Acoustical Society of Korea
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• v.17 no.2
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• pp.71-78
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• 1998

와(vortex) 박리는 고형물체가 유동내에서의 유체의 흐름을 방해할 때 발생하는 전 형적인 주기적 진동 현상이다. 본 연구에서는 삼각주형 실린더가 유동내에 유발하는 와 발 리 특성을 가시화 기법, 와에 의해 변조된 초음파의 파워 스펙트럼 및 유동관에서의 진동측 정 등을 통해 연구하였다. 가시화 관찰과 유동측정 실험 결과, 발생 와는 발생체 전면으로부 터 3d와 5d 사이에서 가장 안정성이 유지됨을 발견하였다. 넓은 레이놀즈 수(104≤Re≤106) 의 유동영역에서 액체와 기체원형유동의 측정 실험결과로부터 스트로우할(Strouhal) 수가 와발생체 폭(d)과 형상비(d/D)의 증가함수이며, 삼각주 단면의 높이에 반비례함을 알 수 있 었다. 또한 실험 결과로부터 실린더의 기하학적 치수로 삼각주형 실린더의 스트로우할 수를 예측할 수 있는 경험식을 제시하였다.

• Proceeding of EDISON Challenge
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• 2012.04a
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• pp.41-44
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• 2012

본 연구에서는 풍력발전에 충분한 가능성을 가진 산악 지형을 모델링하여 유동의 흐름을 분석하였다. 실제 지형(설악산, 점봉산)에 대한 1/500 축소모형을 Gaussian 함수로 표현하였다. EDISON_CFD을 사용하여 산악지형의 난류유동을 해석하였으며, 해석결과의 신뢰성 확인을 위해 격자분해능에 따른 속도분포를 비교하였다. 산악지형에 따른 유동현상을 속도분포 및 유선함수 등에 의해 분석하였다. 또한 풍력터빈 설치 높이 기준에 의거하여 지형변화에 따른 주 유동방향 속도분포를 살펴보았다. 지형효과에 따른 유동해석결과를 기반으로 풍력 발전 가능 영역이 논의되었다.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.4
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• pp.1-10
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• 2001

A numerical solution method of the incompressible Reynolds-Averaged Navier-Stokes equations is applied for calculating turbulent flows and performances of a marine propeller in open-water, four-quadrant conditions. Computed propeller flows of the model propeller P4381, for which the experimental data of the open-water performances exist, reveal complex viscous-flow characteristics including three-dimensional flow separations in various off-design conditions and also computed propeller thrusts and torques agree quite well with experimental data except some cases for which severe propeller cavitations occurred in the experiment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.3
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• pp.285-292
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• 2013

The purpose of this research is to investigate how the boundary layer separation caused by a tripping wire installed in front of the flat plate affects the transition from laminar to turbulent flow, and consequently mass transfer. A naphthalene sublimation technique is used to measure the local mass transfer coefficients on the flat plate, and two boundary conditions for the developed and developing flow are considered to evaluate the effects of the flow boundary. The local mass transfer data for a flat plate with a tripping wire are compared with the data for a flat plate without a tripping wire. The variation trends of the local heat transfer coefficients for the plates with and without the tripping wire are similar to each other in the case of the developing flow, but are quite different for the developed flow. The average Sherwood number for the flat plate with a tripping wire is much higher than that without a tripping wire because of the boundary layer separation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.10
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• pp.954-961
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• 2008

An experimental study has been conducted to investigate the flow field around the wing having a circular damage hole. The damage was represented by a circular hole passing through the model with 10% airfoil chord diameter and normal to the chord. The hole was centered at quarter or half chord. The PIV flow fields and static pressure measurements on the wing upper and lower surface were carried out at Rec=2.85×105 based on the chord length. The PIV results showed the two types of flow structures around a damage hole were formed. The first one was a weak jet that formed an attached wake behind the damage hole. The second one resulted from increased incidence; this was a strong jet where the flow through the hole penetrates into the free-stream resulting in extensive separation of oncoming boundary layer flow and development of a separated wake with reverse flow. The surface pressure data showed a big pressure alteration near the circular damage hole. The severity of pressure alteration was increased as a damage hole located nearer to the leading edge.

• Journal of computational fluids engineering
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• v.18 no.2
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• pp.66-71
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• 2013

In this paper, the supersonic flows around space launch vehicles have been numerically simulated by using a 3-D RANS flow solver. The focus of the study was made for investigating plume-induced flow separation(PIFS). For this purpose, a vertex-centered finite-volume method was utilized in conjunction with 2nd-order Roe's FDS to discretize the inviscid fluxes. The viscous fluxes were computed based on central differencing. The Spalart-Allmaras model was employed for the closure of turbulence. The Gauss-Seidel iteration was used for time integration. To validate the flow solver, calculation was made for the 0.04 scale model of the Saturn-5 launch vehicle at the supersonic flow condition without exhaust plume, and the predicted results were compared with the experimental data. Good agreements were obtained between the present results and the experiment for the surface pressure coefficient and the Mach number distribution inside the boundary layer. Additional calculations were made for the real scale of the Saturn-5 configuration with exhaust plume. The flow characteristics were analyzed, and the PIFS distances were validated by comparing with the flight data. The KSLV-1 is also simulated at the several altitude conditions. In case of the KSLV-1, PIFS was not observed at all conditions, and it is expected that PIFS is affected by the nozzle position.