• EDISON SW 활용 경진대회 논문집
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• 제3회(2014년)
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• pp.521-526
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• 2014

현대에 이르러 초경량 무인 비행기에 대한 많은 연구가 진행되고 있다. 이러한 비행체는 저레이놀즈수 영역에서 사용되는 특성으로 인해, 경계층 내에서 박리현상과 난류영역으로의 천이 등과 같은 여러 복합적인 현상을 발생시킴으로써 비행체의 공력특성에 큰 영향을 미친다. Bumpy Airfoil은 저레이놀즈수 유동에서의 이와 같은 문제를 해결하기 위해 제안된 익형이다. 따라서 본 논문은 전산열유체해석 프로그램인 EDISON_전산열유체를 이용하여 Bumpy Airfoil 형상에 대한 공력특성을 연구하였고, 발생하는 양항비를 원 익형과 비교하였다. 비압축성 조건 내에서, 공력 성능 향상을 위한 Bumpy Airfoil의 형상 변수로 Bump 개수와 높이를 선정하여 받음각에 따른 유동장을 분석하고 양항비를 수치해석 및 고찰하였다.

• International Journal of Fluid Machinery and Systems
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• 제4권1호
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• pp.97-103
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• 2011

With the aim to increase blade loadings and stable operating range in highly loaded compressors, this article has been conducted to explore, through a numerical parametric study, the potential of passive control using slotted bladings in cascade configurations. The objective of this numerical investigation is to analyze the influence of location, width and slope of the slots and therefore identify the optimal configuration. The approach is based on two dimensional cascade geometry, low speed regime, steady state and turbulent RANS model. The results show the efficiency of this passive technique to delay separation and enhance aerodynamic performances of the compressor cascade. A maximum of 28.3% reduction in loss coefficient have been reached, the flow turning is increased with approximately $5^0$ and high loading over a wide range of angle of attack have been obtained for the optimized control parameter.

• 전기의세계
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• 제14권1호
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• pp.35-39
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• 1965

Field problems are solved by a variety of methods. In the relatively small number of cases that are simiple enough, the mathematical attack may be the method of choice. But many field problems with irregular boundary condition must be handled by the use of the electrolitic tank analog, conducting paper or the fluid mapper analog for the purpose of effectiveness and convenience. The method of choice depends on the actual of the problems. There is no one best way to solve all problems. The following points have been described in this apepr, 1. Theoretical studies are made of the vector which is produced by leading the fluid flow vector by a right angle. 2. Curvilinear square method is described., 3. Determination on magnetic flux distribution and variation according to the magnitude of exciting currents.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.627-630
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• 2003

This work presents a numerical procedure to optimize the shape of three-dimensional channel with angled ribs mounted on one of the walls to enhance turbulent heat transfer. The response surface method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of flow and heat transfer. SST turbulence model is used as a turbulence closure. The width-to-height ratio of the rib, rib height-to-channel height ratio, pitch-to-rib height ratio and attack angle of the rib are chosen as design variables. The objective function is defined as a linear combination of heat-transfer and friction-loss related terms with weighting factor. D-optimal experimental design method is used to determine the data points. Optimum shapes of the channel have been obtained for the weighting factors in the range from 0.0 to 1.0.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.520-525
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• 2003

A numerical investigation was performed to determine the effect of airfoil on the optimum flap height using NACA0015 Wells turbine. The five double flaps which have 0.5% chord height difference were selected. A Wavier-Stokes code, CFX-TASCflow, was used to calculate the flow field of the Wells turbine. The basic feature of the Wells turbine is that even though the cyclic airflow produces oscillating axial forces on the airfoil blades, the tangential force on the rotor is always in the same direction. Geometry used to define the 3-D numerical grid is based upon that of an experimental test rig. This paper tries to analyze the optimum double flap of Wells turbine with the numerical analysis.

• International Journal of Fluid Machinery and Systems
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• 제3권4호
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• pp.292-300
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• 2010

This study strives to develop an effective strategy to inhibit cavitation inception on hydrofoils by using local cooling technique. By setting up a temperature boundary condition and cooling a small area on the upper surface of a hydrofoil, the fluid temperature around the cooling surface will be decreased and thereby the corresponding liquid saturation pressure will drop below the lowest absolute pressure within the flow field. Hence, cavitation can never occur. In this paper, a NACA0015 hydrofoil at $4^{\circ}$ angle of attack was numerically investigated to verify the effectiveness of the proposed technique. The CFD results indicate that the cooling temperature and the cooling surface roughness are the critical factors affecting the success of such technique used for cavitation suppression.

• 한국군사과학기술학회지
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• 제5권2호
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• pp.83-90
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• 2002

An experimental study was conducted to investigate the effects of a leading edge extension(LEX) on the vortex flow field over a delta wing by measuring the total pressure distribution in a subsonic wind tunnel. Freestream velocity was 40m/sec and Reynolds number per meter was $1.76{\times}10^6$. The wing with the LEX experienced a strong interaction between the LEX and wing vortices. As the angle of attack increased, the coupled vortex field of these two vortices maintained its strength and concentricity much better than the vortex field over the wing without the LEX.

• 한국군사과학기술학회지
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• 제22권3호
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• pp.360-368
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• 2019

A study on aerodynamic modeling was performed to predict the hinge moments required for initial design of missile. Fin aerodynamic coefficients were modeled using the equivalent angle of attack method based on the wind tunnel test. In addition, CFD analysis was performed to calculate the dynamic pressure around the body and improve the accuracy of aerodynamic coefficients. The aerodynamic coefficient accuracy was verified by comparisons of the coefficient acquired from wind tunnel test and prediction of flow conditions, not involved in the model built-up. It was confirmed that fin aerodynamic coefficients can be predicted effectively by using the proposed method.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.151-158
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• 2009

To implement the insects' flapping flight for developing flapping MAVs(micro air vehicles), the unsteady flow characteristics of the insects' forward flight is investigated. In this paper, two-dimensional FSI(Fluid-Structure Interaction) simulations are conducted to examine realistic flow features of insects' flapping flight and to examine the flexibility effects of the insect's wing. The unsteady incompressible Navier-Stokes equations with an artificial compressibility method are implemented as the fluid module while the dynamic finite element equations using a direct integration method are employed as the solid module. In order to exchange physical information to each module, the common refinement method is employed as the data transfer method. Also, a simple and efficient dynamic grid deformation technique based on Delaunay graph mapping is used to deform computational grids. Compared to the earlier researches of two-dimensional rigid wing simulations, key physical phenomena and flow patterns such as vortex pairing and vortex staying can still be observed. For example, lift is mainly generated during downstroke motion by high effective angle of attack caused by translation and lagging motion. A large amount of thrust is generated abruptly at the end of upstroke motion. However, the quantitative aspect of flow field is somewhat different. A flexible wing generates more thrust but less lift than a rigid wing. This is because the net force acting on wing surface is split into two directions due to structural flexibility. As a consequence, thrust and propulsive efficiency was enhanced considerably compared to a rigid wing. From these numerical simulations, it is seen that the wing flexibility yields a significant impact on aerodynamic characteristics.

• 한국항공우주학회지
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• 제47권12호
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• pp.831-840
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• 2019

플러시 대기자료 측정장치는 비행체 표면에서 측정되는 압력 데이터를 이용하여 대기자료를 예측한다. FADS는 돌출된 프로브가 없으므로 고성능 항공기, 스텔스 비행체 및 극초음속 비행체에 적합하다. 본 논문에서는 구-원추 형상을 갖는 비행체에 대해서 아음속부터 초음속 비행까지 대기자료를 예측할 수 있는 FADS의 교정 절차와 계산 알고리즘을 제시한다. 표면 압력 데이터 측정을 위해 노즈부 표면에 5개 플러시 압력공들을 마련하였다. 유동각 예측과 압력 관련 변수의 예측을 분리하는 개념이며, 아음속 유동의 포텐셜 유동해와 극초음속 유동의 수정 뉴톤식을 결합한 압력모델을 사용한다. 교정 압력 데이터는 Euler 방정식을 푸는 전산유체역학 코드를 만들어서 마흐수 0.5 ~ 3.0의 범위에서 구축하였다. 비행 마흐 수 0.6~3.0, 받음각과 옆미끄럼각은 각각 -10° ~ +10°의 범위에서 여러 비행조건에 대해서 테스트를 수행하였다. 예측된 대기자료는 받음각, 옆미끄럼각, 마흐수, 자유류 정압이며 참고 데이터와 비교하여 정확도를 분석하였다.