• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1566-1569
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• 2008

The flow visualization is conducted in order to investigate an unsteady flight characteristic of a model dragonfly. The flapping wings are analyzed using smoke-wire and high speed camera. The results of this experiment show that three mechanisms and high incidence angle of the wings are responsible for the lift. The leading edge vortex, which is induced by the rapid acceleration of the wing at the beginning of a stroke, causes the lift enhancement. The delayed stall during the stroke and the fast supination and pronation of the wing near the end of each stroke are also responsible for the lift generation.

• Journal of Advanced Marine Engineering and Technology
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• 제27권5호
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• pp.666-674
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• 2003

An experimental investigation was performed to study the characteristics of turbulent swirling flow in an axisymmetric annuli. The swirl angle measurements were performed by flow visualization technique using smoke and dye liquid along the test tube. Using the Particle Image Velocimetry method, this study found the time-mean velocity distribution and turbulent intensity with swirl for Re = 20.000. 30.000, 50.000. and 70.000 along longitudinal sections and the results appear to be physically reasonable.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1586-1591
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• 2004

Flow visualization experiments have been performed to investigate the effects of phase lag, reduced frequency qualitatively by examining wake pattern on a dragonfly type wing. The model was built with a scaled-up, flapping wings, composed of paired wings with fore- and hindwing in tandem, that mimicked the wing form of a dragonfly. The present study was conducted by using the smoke-wire technique, and an electronic device was mounted to find the exact positional angle of wing below the tandem wings, which amplitude is ranged from $-16.5^{\circ}$ to $+22.8^{\circ}$. Phase lag applied on the wings is $0^{\circ}$, $90^{\circ}$, $180^{\circ}$ and $270^{\circ}$. The reduced frequency is 0.15, 0.3 and 0.45 to investigate the effect of reduced frequency. It is inferred through observed wake pattern that the phase lag clearly plays an important role in the wake structures and in the flight efficiency as changing the interaction of wings. The reduced frequency also is closely related to wake pattern and determines flight efficiency.

• 한국추진공학회지
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• 제15권2호
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• pp.29-35
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• 2011

고체로켓모터 추진제 그레인의 핀-슬롯 표면에서의 연소로 인해 생성된 고온, 고압의 연소가스는 그레인 핀-슬롯 및 내삽노즐을 통해 외부로 방출되면서 형성되는 유동은 매우 복잡하고 다양한 형태를 가진다. 핀-슬롯형 그레인 및 내삽노즐을 가지는 고체로켓모터의 2D, 3D 스케일모델에 대한 공기유동 모사시험을 수행하였으며, 롤토크 발생 등과 같은 내부유동발생 메커니즘을 규명할 수 있는 효과적인 연기-유동장 가시화 기법의 적용방법에 대한 검토가 이루어 졌다. 다양한 광원조사기법 및 촬영장치 방향을 이용하여, 축류 실험모델 노즐 선단부에서의 비대칭 와류튜브에 의한 선회류를 가시화하였다.

• 한국가시화정보학회지
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• 제8권1호
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• pp.53-60
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• 2010

Experimental investigations were conducted to study the characteristics of turbulent swirling flow in an axisymmetric annuli. Swirl angle measurements were performed using a flow visualization technique using smoke and dye liquid for Re=60,00080,000. Using the two-dimensional particle image velocimetry method, we found the time-mean velocity distribution and turbulent intensities in water with swirl for Re=20,000, 30,000, and 40,000 along longitudinal sections. Neutral points occurred for equal axial velocity at y/(R-r)=0.70.75, and the highest axial velocity was recorded near y/(R-r)=0.9. Negative axial velocity was observed near the convex tube along X/(D-d)=3~23. Another experimental study was performed to investigate heat transfer characteristics of turbulent swirling flow in an axisymmetric annuli. Static pressure, and local flow temperature were measured using tangential inlet condition and the friction factors and Nusselt number were calculated for several Reynolds numbers.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.181-185
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• 2010

고체로켓모터 추진제 그레인의 핀-슬롯 표면에서의 연소로 인해 생성된 고온, 고압의 연소가스는 그레인 핀-슬롯 및 내삽노즐을 통해 외부로 방출되면서 형성되는 유동은 매우 복잡하고 다양한 형태를 가진다. 핀-슬롯형 그레인 및 내삽노즐을 가지는 고체로켓모터의 2D, 3D 스케일모델에 대한 공기유동 모사시험을 수행하였으며, 회전력 발생 등과 같은 내부유동발생 메커니즘을 규명할 수 있는 효과적인 연기-유동장 가시화 기법의 적용방법에 대한 검토가 이루어 졌다. 실험모델의 투영부를 통해 다양한 광원 및 촬영장치 방향을 이용하여, 축류 실험모델 노즐 선단부에서의 비대칭 와류튜브에 의한 선회류를 가시화하였다.

• 한국화재소방학회논문지
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• 제24권1호
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• pp.90-94
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• 2010

본 연구에서는 횡류환기방식의 균일배기방식(balanced exhaust)에 대한 터널 내 풍속, 배연풍량에 따른 수치해석을 수행하여 연기의 이동거리를 분석하고 기존의 유동가시화 실험결과와 비교하였다. 그 결과 균일배기방식의 배연시스템에서는 풍속이 존재하지 않는 경우 배연풍량을 연기발생량(Vc = 0)일 때 건설교통부의 도로터널방재시설 지침에 의한 피난연결통로의 간격 250m 이내로 연기가 제한되었으며, 배연효율은 본 실험범위에서 55.1%에서 95.8%로 나타났다. 터널 내 풍속이 존재하면 연기를 배연하기 위한 배연풍량이 급격하게 증가하는 경향을 보이는 것으로 알 수 있으며, 배기구의 풍속이 증가하면 배연효율이 감소하며, 연기의 이동거리를 목표로 하는 거리로 제한하기 위해서 배연풍량은 연기발생량 보다 최대 1.8배에서 1.04배까지 증대하는 것으로 나타나고 있다. 본 연구에서 평가기준으로 선정한 250m 이내로 연기의 이동거리를 제한하기 위한 배연풍량은 터널 내 풍속이 존재하지 않는 경우에는 배연풍량은 최소 $84m^3/s{\cdot}250m$, 1.75m/s인 경우에 배연풍량은 최소 $393m^3/s{\cdot}250m$($Q_E$= 80 + 5Ar)으로 나타났다.

• International Journal of Automotive Technology
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• 제6권1호
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• pp.15-21
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• 2005

The purpose of this paper is to experimentally investigate the engine pollutant emissions and combustion characteristics of diesel engine fueled with ethanol-diesel blended fuel (bio-diesohol). The experiments were performed on a single-cylinder DI diesel engine. Two blend fuels were consisted of $15\%$ ethanol, $83.5\%$ diesel and $1.5\%$ solublizer (by volume) were evaluated: one without cetane improver (E15-D) and one with a cetane improver (E15-D+CN improver). The engine performance parameters and emissions including fuel consumption, exhaust temperature, lubricating oil temperature, Bosch smoke number, CO, NOx, and THC were measured, and compared to the baseline diesel fuel. In order to gain insight into the combustion characteristics of bio-diesohol blends, the engine combustion processes for blended fuels and diesel fuel were observed using an Engine Video System (AVL 513). The results showed that the brake specific fuel consumption (BSFC) increased at overall engine operating conditions, but it is worth noting that the brake thermal efficiency (BTE) increased by up to $1-2.3\%$ with two blends when compared to diesel fuel. It is found that the engine fueled with ethanol-diesel blend fuels has higher emissions of THC, lower emissions of CO, NOx, and smoke. And the results also indicated that the cetane improver has positive effects on CO and NOx emissions, but negative effect on THC emission. Based on engine combustion visualization, it is found that ignition delay increased, combustion duration and the luminosity of flame decreased for the diesohol blends. The combustion is improved when the CN improver was added to the blend fuel.

• 한국항공우주학회지
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• 제32권8호
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• pp.72-81
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• 2004

초고속 지상 운행체에 대한 풍동실험을 통하여 단단한 채널과 운행체 사이에 발생하는 공력 상호작용을 연구하였다. 풍동실험시 유속은 30m/see에서, 단위길이당 레이놀즈수는 $3.1{\times}10^5/m$였다. 가변지면과 안내로와 같은 실험장치들이 이 실험을 위해 사용되었다. 운행체는 지면과 운행체 사이의 거리가 가까워질수록, 안내로 사이의 간격이 좁아질수록 양력은 급격히 증가하였고, 항력은 미세하게 감소하였으며, 키놀이 모멘트는 억제되어 정안 정성을 증대시켰다. 연선을 사용한 유동가시화를 통하여 운행체가 채널 내를 운행할 때의 유동 특성을 채널이 없는 경우와 비교하였고 공력측정 결과를 뒷받침하였다. 채널 지연과 안내로의 영향으로, 운행체 하부에서의 유동은 날개의 익단판 외부로 흐르지 못하며, 이것이 운행체 양력증가의 주요 원인이 되었다.

• International Journal of Aeronautical and Space Sciences
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• 제18권1호
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• pp.8-16
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• 2017

Most of small air vehicles with moving wing fly at low Reynolds number condition and the reduced frequency of the moving wing ranges from 0.0 to 1.0. The physical phenomena over the wing dramatically vary with the reduced frequency. This study examines experimentally the effect of the reduced frequency at low Reynolds number. The NACA0012 airfoil performs sinusoidal pitching motion with respect to the quarter chord with the four reduced frequencies of 0.1, 0.2, 0.4 and 0.76 at the Reynolds number $2.3{\times}10^4$. Smoke-wire flow visualization, unsteady surface pressure measurement, and unsteady force calculation are conducted. At the reduced frequency of 0.1 and 0.2, various boundary layer events such as reverse flow, discrete vortices, separation and reattachment change the amplitude and the rotation direction of the unsteady force hysteresis. However, the boundary layer events abruptly disappear at the reduced frequency of 0.4 and 0.76. Especially at the reduced frequency of 0.76, the local variation of the unsteady force with respect to the angle of attack completely vanishes. These results lead us to the conclusion that the unsteady aerodynamic characteristics of the reduced frequency of 0.2 and 0.4 are clearly distinguishable and the unsteady aerodynamic characteristics below the reduced frequency of 0.2 are governed by the boundary layer events.