• 한국추진공학회지
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• 제15권4호
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• pp.41-47
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• 2011

75톤급 개방형 액체로켓 엔진에 장착되는 터보펌프의 터빈은 초음속 충동형 방식이다. 본 연구에서는 터빈 로터 앞전 두께가 성능에 미치는 영향을 실험을 통해 살펴보았다. 터빈 시험에서는 2가지 다른 앞전 두께를 가진 로터를 이용해 실험하였으며, 각 로터는 앞전 두께 대 피치비가 30톤 로터 대비 각각 1.9배와 1.4배이다. 시험 결과 로터 두께가 1.4배인 로터의 설계 상사점 효율이 1.5% 상승하였고, 동일 회전수에서 최대 효율이 나타나는 압력비도 완전팽창비 쪽으로 증가하였다.

• 전력전자학회논문지
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• 제12권3호
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• pp.241-247
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• 2007

LLC 하프브리지 다중 출력용 컨버터의 보조 출력부와 같이, 펄스 전압을 입력으로 갖는 PWM 컨버터에서는 출력 정전압 제어를 위하여 스위치의 턴 온 제어 방식을 필요로 한다. 본 논문에서는 전류 불연속 모드로 동작하는 벅 컨버터의 새로운 도통시간 턴 온 제어방식에 대하여 논하였다. 제안된 LEM 제어 방식의 PWM 동작 원리를 설명하였으며, 임펄스 응답 이론을 근거로 인덕터 전류의 소신호 주파수 응답 특성을 고찰하였다. 또한 60인치 PDP 어드레스용 100W급 파워 모듈에 적용함으로서 제안된 제어 방식의 타당성을 검증하였다.

• 산업공학
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• 제15권4호
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• pp.432-438
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• 2002

When the trailing edge and leading edge of an airfoil contour of high pressure compressor blades are measured, there exists a measurement error due to the size of the probe stylus ball diameter. In the paper an experimental study is provided to determine the optimum diameter of the probe stylus in inspecting the airfoil of the high pressure compressor blade. The measurement and analysis procedure suggested in this paper will be helpful to those who are involved in measuring and inspecting various types of blades.

• 항공우주시스템공학회지
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• 제13권5호
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• pp.32-38
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• 2019

높은 후퇴각을 갖는 둥근 앞전 날개 형상은 앞전 와류에 의해 복잡한 유동 현상이 나타난다. 불안정한 방향 안정성을 갖는 무미익 플라잉윙의 제어를 위해서 플래퍼론이 사용된다. 본 연구에서는 플래퍼론이 전개된 비세장형, 둥근 앞전의 플라잉윙 형상의 전산해석을 수행하였으며 옆미끄럼각 및 플래퍼론에 대한 영향을 분석하였다. 공력계수 분석을 통해 양력과 항력계수에 대한 옆미끄럼각의 영향은 적으며 측력 및 모멘트 계수는 옆미끄럼각의 영향을 크게 받음을 알 수 있었다. 정적 안정성 분석을 통해 플래퍼론이 전개된 플라잉윙의 가로안정성과 방향안정성이 좋아졌음을 확인하였다. 또한 압력계수분포, 표면 마찰선의 관찰을 통해 앞전 와류 구조 및 거동을 분석하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.43-50
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• 2009

In order to reduce the download around Smart UAV(SUAV) at hovering and transition mode, flow control using synthetic jet has been performed. Many of the complex tilt rotor flow features are captured including wing leading and trailing edge separation, and the large region of separated flow beneath the wing. First, in order to control the trailing edge separation, synthetic jet is located at 30, 95% of flap chord length. The flow control using synthetic jet on flap shows that stall characteristics depending on several mode can be improved through separation vortices resizing. Also, a flap jet and a 0.01c jet which control the separation efficiently are applied at the same time at each test case because controlling the leading edge separation is essential for download reduction. As a result, time averaged download is reduced about 18% comparing with no control case at hovering mode and 48% at transition mode. These research results show that if flow control using leading edge jet and trailing edge jet is used effectively to the SUAV in overall flight mode, flight performance and stability can be improved.

• 동력기계공학회지
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• 제11권3호
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• pp.53-58
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• 2007

The ruptured blade which is rotating at high speed can damage severely the all stage compressor blades and the turbine components. If the shattered blades flow downstream inside the turbine parts, then the turbine blades and vanes can be damaged. The small parts of shattered blades which are flowed into the turbine parts pass through without any damages in the leading edge of the first stage stationary blades. Then they bump against the convex side of the leading edge of the first stage moving blades and the trailing edge of the first stage stationary blades repeatedly. The debris of shattered blades may plug the cooling holes in the turbine blades and vanes. The dent damage and the coating delamination could be also occurred by the debris of shattered blades flowed downstream inside the combustion liner and the transition piece. This paper analyzes the influence on the turbine components and the damage mechanism and characteristics in case of the damaged blade of the multiple-stage axial flow compressor.

• 한국소음진동공학회논문집
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• 제17권12호
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• pp.1223-1229
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• 2007

Flow traveling over a cavity opening forms a vortex due to unstable shear layer and induces an aerodynamic pressure excitation from the diffusion of the vortex convecting out of the trailing edge of the opening. The interaction between the excitation force and the cavity response sustains resonance in the resonator(cavity) and locked-in vortex shedding at the leading edge of the opening. The aerodynamic excitation force can be described from the diffusion of the vortex over the trailing edge and the level of its diffusivity is related to the strength of vorticity seeded at the leading edge. In this study, the control scheme of the internal pressure oscillation was proposed from regulating the vorticity at the leading edge by use of an oscillating spoiler. It was found that the relative motion between the spoiler and the air mass at the cavity opening influenced vorticity strength and the control was achieved by direct feedback of the cavity pressure fluctuation to the actuator.

• Journal of Mechanical Science and Technology
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• 제17권6호
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• pp.914-924
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• 2003

The interaction and breakdown of vortices over the Leading Edge Extension (LEX) - Delta wing configuration has been investigated through wing-surface pressure measurements, the off-surface flow visualization, and 5-hole probe measurements of the wing wake section. The description focused on analyzing the interaction and the breakdown of vortices depending on the angle of attack and the sideslip angle. The Effect of angle of attack and sideslip angle on the aerodynamic load characteristics of the model is also presented. The sideslip angle was found to be a very influential parameter of the vortex flow over the LEX-delta wing configuration. The introduction of LEX vortex stabilized the vortex flow, and delayed the vortex breakdown up to a higher angle of attack. The vortex interaction and breakdown was promoted on the windward side, whereas it was suppressed on the leeward side.

• 대한조선학회논문집
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• 제37권1호
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• pp.60-66
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• 2000

고속 프로펠러를 대상으로 캐비테이션 발생 특성에 가장 큰 영향을 미치는 2차원 날개단면의 앞날 형상에 관한 연구를 수행하였다. 앞날 주위의 유동장을 해석하기 위하여 비압축성 RANS(Reynolds Averaged Navier-Stokes)방정식을 유한체적법(FVM)으로 차분하는 수치해석기법을 사용하였다. 또한 패널법을 이용하여 캐비테이션 발생두께를 예측하였다. 예측된 결과들은 실험결과와 비교해서 타당함을 알 수 있었으며, 이 결과를 이용하여 새로운 단면을 설계하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.291-293
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• 2003

This paper deals with a thrust generation of flapping-airfoil by dynamic stall. From many other previous research results, phase angle $ between pitching and plunging mode of flapping motion must be 90 deg. to satisfy maximum propulsive efficiency. In this case, leading edge vortex is relatively small. This phenomenon is related dynamic stall. So preventing leading edge vortex induced by dynamic stall guarantees maximum propulsive efficiency. But, in this paper we insist the leading edge vortex yields quite a positive influence on thrust generation and propulsive efficiency. In order to certify our opinion, pitching and plunging motions were calculated with the parameter of amplitude and frequency by using the unsteady, incompressible Navier-Stokes flow solver with a two-equation turbulence model. For more efficient computation, it is parallelized by MPI programming method.