• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.60-66
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• 2007

Separation control has been performed using synthetic jets on airfoil at high angle of attack. Computed results demonstrated that stall characteristics and control surface performance could be substantially improved by resizing separation vortices. It was observed that the actual flow control mechanism and flow structure is fundamentally different depending on the range of synthetic jet frequency. For low frequency range, small vortices due to synthetic jet penetrated to the large leading edge separation vortex, and as a result, the size of the leading edge vortex was remarkably reduced. For high frequency range, however, small vortex did not grow up enough to penetrate into the leading edge separation vortex. Instead, synthetic jet firmly attached the local flow and influenced the circulation of the virtual airfoil shape which is the combined shape of the main airfoil with the separation vortex. Theses results show the characteristic of unsteady flow of single synthetic jet. Beside, we researched on multi-array synthetic jet to obtain applicable synthetic jet velocity. Multi-location synthetic jet is proposed to eliminate small vortex on suction surface of airfoil. With the results, we concluded that the flow around airfoil is stable by high frequency synthetic jet with elimination of small vortex and confirmation of stable flow. Moreover, performance of multi-array/multi-location synthetic jet can be improved by changing phase angle of multi-location synthetic jet.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.12
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• pp.1173-1183
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• 2009

In order to reduce the download around the Smart UAV(SUAV) at hovering, flow control using synthetic jet has been performed. Many of the complex tilt rotor flow features are captured including the leading and trailing edge separation, and the large region of separated flow beneath the wing. In order to control the leading edge and trailing edge separation, synthetic jet is located at 0.01c, $0.3c_{flap}$, $0.95c_{flap}$. As non-dimensional frequency, the flow pattern is altered and the rate of drag reduction is changed. The results show that synthetic jets shorten the vortex period and decrease the vortex size by changing local flow structure. By using leading edge jet and trailing edge jet, download is efficiently reduced compared to no control case at hovering mode.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.256-256
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• 2009

에폭시수지에 층상실리케이트 나노입자를 충진함량별로 충진시킨 나노콤포지트를 제조하여 충진함량의 변화와 분산제 첨가를 통하여 분산제효과를 조사하였다, 충진함량의 변화는 1, 3, 5, 7, 9wt%과 분산제 변화를 05, 1.5, 2.5wt%로 구조적, 열적, 전기적 특성을 조사하였다. 분산처리는 초음파 기법을 적용하여 분산하였다. 구조적 특성으로 X-RD조사한 결과 0.5wt%분산제처리를 한 경우 완전한 박리를 가져오지 못하였고, 부분적인 박리를 가져왔다. 이는 분산제 처리량이 나노입자 표면정체를 제어할수 없기 때문으로 사료된다. 분산제 1.5wt%를 첨가한경우로 충진함량별 X-RD특성은 1wt%는 완전한 박리를 나타내었고 함량의 증가에 따라 박리정도가 약간 낮아지는 경우를 알 수 있다. 이런 경우 전기적특성중 단시간 절연파괴특성에서 나타내고 있다. 충진함량이 낮을수록 스케일파라미터의 값이 높고, 함량이 증가할수록 낮아지는 경우이다. 이는 분산정도에따라 절연파괴강도에 영향을 주고 있음을 알 수 있다. 열적특성에서 유리천이온도는 1,3,5wt%에서는 증가하는 결과를 더욱 충진함량이 증가하면 오히려 감소되는 특성을 나타내고 있다. 결국은 분산정도에따라 전기적 특성 및 열적특성이 크게 변화되는 특성을 나타내었다.

• Journal of Korean Society of Steel Construction
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• v.20 no.6
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• pp.751-759
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• 2008

In this study, the effect of an unsteady flow field around a body of aerostatic/aerodynamic forces were investigated using rectangular cylinders (B/D = 2, 3, 4, 5). Proper orthogonal decomposition (POD) was introduced to the analysis of the fluctuating pressure field that was measured on the stationary/oscillatory B/D=4 rectangular cylinder, and the characteristics of the proper functions with flow patterns were identified. In addition, the physical decoupling and interactions in the different co-existing flow patterns were investigated through POD. The comparison with the identified proper function associated with a particular flow pattern revealed that the Karman vortex is almost not affected by the separation bubble, but that the Karman vortex considerably interferes in the development of the separation bubble around the trailing edge. It can be considered that the Karman vortex induces the increment of the curvature of the substantial separated flow.

• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.57-64
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• 2005

Aerodynamic characteristics of three-dimensional wings in ground effect for Aero-levitation Electric Vehicle(AEV) are numerically investigated for various fairing shapes at the junctions of 3D Wings. Numerical results show that a sizeable three-dimensional comer flow separation occurs with formation of an arch vortex at the junction of main and vertical wings, and also that this is predicted the main cause of the high lift-to-drag(L/D) reduction rate of the main wing. To avoid the comer flow separation, the main idea of this study is to reduce the cross section gradient of the comer flow tube near the trailing edge for various fairing shapes. Improvements on L/D ratios of the wings are pursued by breaking the coherence of superimposed adverse pressure gradients at the wing junction when the cross section gradient is changed slowly at the trailing edge.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.211-211
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• 2014

스퍼터링에 의한 박막의 형성에서 박막의 박리나 기판의 휨은 박막내의 내부 응력과 깊은 관련이 있다. 특히 Ti/TiN구조로 많이 사용되는 TiN은 반도체 barrier 층으로 사용이 되기도 하며 하드 코팅 재료로도 많은 연구가 이루어지고 있다. 특히 TiN에 존재하는 높은 압축응력은 연성기판재나 무른 금속재질의 기판을 휘게도 하며, 심할 경우 박막의 박리 현상이 자주 관찰된다. 이렇게 높은 스트레스를 제어하기 위한 기초 연구로 다양한 금속층 박막의 스트레스와 완화시키기 위한 공정 조건 및 스트레스 특성을 확인하였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.248-248
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• 2012

실리콘 산화막 기판 및 퀄츠 기판 위에 그래핀을 기계적으로 박리시킨 후, 두께 1 nm 이하의 금 박막을 증착한 후 고온 열처리를 통하여 금 박막으로부터 나노입자의 형성 거동을 살펴보았다. 열처리 후 생성되는 금 나노입자는 실리콘 산화막 및 퀄츠기판 보다 그래핀 위에서 더 크게 형성되는 것을 확인하였으며, 이는 금의 표면확산 정도가 그래핀 위에서 더 크다는 것을 의미한다. 또한 동일 박리 그래핀 위에서도 그래핀의 층 수에 따라 형성되는 금 나노입자의 크기가 달라짐이 확인되었다. 열처리에 의해 형성된 다양한 크기의 금 나노입자는 단일벽 탄소나노튜브(SWNTs)의 직경제어 합성을 위한 촉매로 이용하였다.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.1
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• pp.94-100
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• 2012

The passive control by vertical splitter plate of fluid force acting on a square prism near a plane wall was studied by measuring of fluid force on the prism and by visualization of the flow field using PIV. The hight of the splitter plate was 10% of the square width. The experimental parameters were the attaching position of vertical splitter plate and the space ratios G/B to the prism height. Time variation of vorticity was most remarkable at 3.0B(B: prism height) position toward wake direction from the center of the prism. The point of inflection of average lift coefficient and Strouhal number on the prism were represented at the space ratio G/B=0.4~0.6 for the prism having vertical splitter plate. The drag of the prism was reduced average 5.0% with the space ratios by attaching the vertical splitter plate at the upper and rear corner on the prism. In this case, the size of the separated region on the upside of the prism was smaller than that of prism having no the splitter plate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.12
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• pp.1025-1031
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• 2012

The present paper deals with concept design of supersonic inlet based on compressible flow theory and flow control of bleeding in order to guarantee stability of supersonic inlet of ramjet engine in broad range of operating conditions. Shock instability, shock wave-boundary layer interaction and flow separation should be properly controlled to improve performance of the supersonic inlet. Considering shock strength, boundary layer and flow separation, the supersonic inlet is modified from the basic model which is designed under inviscid theory. Consequently, shock is stabilized, and required mass flow rate is obtained. Furthermore, bleeding is applied to the supersonic inlet to maintain performance in off-design conditions. Mass flow condition is adopted for modeling of bleeding effect, and performance of the supersonic inlet is evaluated by changing bleeding locations and numbers.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.5
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• pp.10-17
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• 2004

To achieve the advanced forward flight performance of helicopter, the passive control methods for enhancement of the dynamic stall characteristics of rotor blades are studied. To enhance the dynamic stall characteristics of the rotor blades, it is essential to improve the lift performance and the pitching moment performance simultaneously with the control of the separation on the rotor blades. For this point of view, both the fixed droop leading edge and the Gurney flap which are simply realized are used for control of the dynamic stall in severe dynamic stall conditions. From this study, the combination of both passive control methods showed dramatic enhancement of lift and pitching moment performance in dynamic stall than previous research results.