• 한국항공운항학회지
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• 제6권1호
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• pp.7-20
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• 1998

A reduction of induced drag is an important problem in order to save fuels. In this study, the aerodynamic characteristics of wing tip devices to reduce induced drag, such as end plate, plain ring, helical ring wing tip device, was experimentally investigated in a low speed wind tunnel. The experimental results showed that the wing model with a helical ring wing tip device reduced a induced drag and increased lift-drag ratio.

• 한국태양에너지학회 논문집
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• 제33권1호
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• pp.40-47
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• 2013

An aerodynamic design tool was developed for small wind turbine blades based on the blade element momentum theory. The lift and drag coefficients of blades that are needed for aerodynamic blade design were obtained in real time from the Xfoil program developed at University of Illinois. While running, the developed tool automatically accesses the Xfoil program, runs it with proper aerodynamic and airfoil properties, and finally obtains lift and drag coefficients. The obtained aerodynamic coefficients are then used to find out optimal twist angles and chord lengths of the airfoils. The developed tool was used to design a wind turbine blade using low Reynolds number airfoils, SG6040 and SG6043 to have its maximum power coefficient at a specified tip speed ratio. The performance of the blade was verified by a commercial code well known for its prediction accuracies.

• 대한기계학회논문집 C: 기술과 교육
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• 제3권3호
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• pp.233-240
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• 2015

본 연구에서는 다양한 형상변수들이 봅슬레이의 공력성능에 미치는 영향을 평가하기 위하여 삼차원 Reynolds-averaged Navier-Stoke 해석을 수행하였으며, 난류모델로는 표준 k-${\varepsilon}$ 모델이 사용하였다. 격자계로는 비정렬 사면체 격자를 사용하였다. 성능 평가를 위한 형상변수로는 전방범퍼의 장축의 길이, 범퍼의 높이, 그리고, 카울링 측면과 정면 각각에서의 곡률반경 등 네가지 변수를 설정하였으며. 이들이 공력성능으로 선정된 항력계수에 미치는 영향을 평가하였다. 해석결과, 범퍼의 높이와 카울링 측면의 곡률반경이 항력계수에 민감한 영향을 미침을 알 수 있었다.

• 기술사
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• 제18권3호
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• pp.64-71
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• 1985

• 한국추진공학회지
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• 제19권1호
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• pp.25-32
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• 2015

원통 모델에 공기저항저감 효과를 검증하기 위해서 원통형에 적합한 유연성 플라즈마 구동기를 제작하였다. 다양한 풍속에서 플라즈마 유동제어 풍동시험을 수행하였으며, CFD 해석과 유동가시화를 수행하였다. 풍속이 느린 저속 구간에서는 유동박리가 발생하지 않아 플라즈마 유동제어 효과가 없었다. 풍속 14 m/s 에서 14% 정도 항력이 저감되었으며, 풍속이 증가된 17 m/s 의 경우 항력이 27% 저감되었다. CFD 해석과 유동가시화의 비교를 통해 DBD플라즈마 구동기는 원통 주변의 압력차를 감소시켜 와류의 크기가 줄어든 것으로 확인되었다.

• 한국철도학회논문집
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• 제18권4호
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• pp.279-288
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• 2015

다양한 3차원 전두부 형상을 효과적으로 모델링할 수 있는 열차형상함수를 이용하여 실제 차량인 KTX 산천 전두부 형상의 공기저항을 저감하는 최적설계를 수행하였다. KTX 산천 전두부의 2차원 단면형상의 특성 곡선을 추출하고 열차형상함수를 이용하여 KTX 산천의 최적설계용 유선형 기본형상을 구성하였다. 기본형상을 이용해 상용 고속열차 전두부의 형상 제약조건을 위반하지 않는 설계공간을 구축하였다. Broyden-Fletcher-Goldfarb-Shanno 알고리즘을 이용한 최적설계를 수행하여 기본형상 대비 약 6%의 공기저항을 저감할 수 있었다. 최적형상은 기본형상에 비해 전두부 길이가 길고 끝단이 약간 날카로운 형상을 가져 후미차량에서의 와류의 크기를 줄임으로써 공기저항을 저감하였다.

• Wind and Structures
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• 제11권4호
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• pp.257-273
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• 2008

A number of passive aerodynamic drag reduction methods were applied separately and then in different combinations on an intercity bus model, through wind tunnel studies on a 1:20 scale model of a Mercedes Benz Tourismo 15 RHD intercity bus. Computational fluid dynamics (CFD) modelling was also conducted in parallel to assist with flow visualisation. The commercial CFD package $CFX^{TM}$ was used. It has been found that dramatic reductions in coefficient of drag ($C_D$) of up to 70% can be achieved on the model using tapered and rounded top and side leading edges, and a truncated rear boat-tail. The curved front section allows the airflow to adhere to the bus surfaces for the full length of the vehicle, while the boat-tails reduce the size of the low pressure region at the base of the bus and more importantly, additional pressure recovery occurs and the base pressures rise, reducing drag. It is found that the CFD results show remarkable agreement with experimental results, both in the magnitude of the force coefficients as well as in their trends. An analysis shows that such a reduction in aerodynamic drag could lead to a significant 28% reduction in fuel consumption for a typical bus on intercity or interstate operation. This could translate to a massive dollar savings as well as significant emissions reductions across a fleet. On road tests are recommended.

• 산업기술연구
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• 제22권B호
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• pp.27-34
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• 2002

3-D numerical studies are performed to investigate the effect of the air dam height and approaching air velocities on the pressure distribution of notchback road vehicle. For this purpose, the models of test vehicle with four different air dam heights are introduced and PHOENICS, a commercial CFD code, is used to simulate the flow phenomena and to estimate the values of pressure coefficients along the surface of vehicle. The standard $k-{\varepsilon}$ model is adopted for the simulation of turbulence. The numerical results show that the height variation of air dam makes almost no influence on the distribution of the value of pressure coefficient along upper and rear surface but makes strong effects on the bottom surface. That is, the value of pressure coefficient becomes smaller as the height is increased along the bottom surface. Approaching air velocity makes no differences on pressure coefficients. Through the analysis of pressure coefficient on the vehicle surface, one tries to assess aerodynamic drag and lift of vehicle. The pressure distribution on the bottom surface affects more on lift than the pressure distribution on the upper surface of the vehicle does. The increase of air dam height makes positive effects on the lift decrease but no effects on drag reduction.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1995년도 추계 학술대회논문집
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• pp.154-159
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• 1995

Numerical optimization technique with Navier-Stokes code has been used to reduce the drag of conventional ogival nose. Forebody optimizations are performed for supersonic laminar and turbulent flow conditions. To alleviate the computing time of aerodynamic drag calculation, axisymmetric boundary condition is implemented in the 3-dimensional Navier-Stokes code. The automated optimization procedure with gradient based method results in a drag reduction of $4\;\%$.

• 한국자동차공학회논문집
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• 제18권5호
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• pp.100-107
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• 2010

This paper gives new conceptual descriptions of drag reduction mechanism owing to rotating wheel and moving ground condition when dealing with automotive aerodynamics. Using Computational Fluid Dynamics (CFD), flow simulation of three dimensional automobile configuration made by Vehicle Modeling Function (VMF) is performed and the influence of wheel arch, wheels, rotating wheel & moving ground condition to the automotive aerodynamic performance is analyzed. Finally, it is shown that rotating wheel & moving ground condition decreases automotive aerodynamic drag owing to the reduction of the induced drag led by the decrease of COANDA flow intensity of the rear trunk flow.