• 대한기계학회논문집 C: 기술과 교육
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• 제2권1호
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• pp.29-37
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• 2014

본 연구에서는 저 레이놀즈수에서의 Kline-Fogleman 익형과 이를 적용한 날개의 공력특성을 분석하였다. 레이놀즈수 $2.4{\times}10^5$ 이하 영역에서 양항비가 향상됨을 확인하였으며, 특히 레이놀즈수 $1{\times}10^4$에서 양항비가 26% 향상되었다. 양항비 측면에서 Kline-Fogleman 익형이 날개 중앙에 위치하는 것이 가장 유리하며, 전체 날개에 대한 Kline-Fogleman 익형의 면적이 80%일 때 양항비가 20% 증가함을 확인하였다. 이 때 항속시간은 12% 향상되었다. 또한 날개의 구조적 안정성과 양항비 향상률을 고려하였을 때 Kline-Fogleman 익형의 면적을 50%에서 80%사이로 설계하는 것이 유리할 것으로 판단된다.

• 한국항공우주학회지
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• 제34권3호
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• pp.6-13
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• 2006

본 연구에서는 저 레이놀즈수 유동에서 flapping운동을 하는 익형이 가질 수 있는 2차원 평면상의 운동궤적에 따른 공력특성을 연구하였다. 익형이 유동흐름방향으로 왕복 운동하는 lead-lag운동과 plunging운동의 조합으로 2차원 평면상에 나타날 수 있는 여러 운동궤적을 합성하여 flapping 주파수 변화에 따른 공력계수들의 변화를 살펴보았다. 상하방향의 순수 plunging운동에 lead-lag운동을 추가함으로써, 평균추력계수와 평균양력계수를 증가시킬 수 있는 운동궤적이 존재함을 확인하였다. 아울러 운동주기 동안 나타나는 추력계수와 양력계수의 변화를 비교하여 upstroke와 downstroke시 나타나는 공력특성을 파악하였다.

• International Journal of Aerospace System Engineering
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• 제2권1호
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• pp.6-11
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• 2015

An active flow control technique using blowing and distributed suction on low Reynolds airfoil is investigated. Simultaneous blowing and distributed suction can recirculate the jet flow mass, and reduce the penalty to propulsion system due to avoiding dumping the jet mass flow. Energy is injected into main flow by blowing on the suction surface, and the low energy boundary flow mass is removed by distributed suction, thus the flow separation can be successfully suppressed. Aerodynamic lift to drag ratio is improved significantly using the flow control technique, and the energy consumption is quite low.

• 한국가시화정보학회지
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• 제4권2호
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• pp.44-50
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• 2006

A visualization study on the boundary layer and near-wake of an NACA 0012 airfoil was con-ducted in order to investigate the influence of boundary layer behavior on the near-wake at low Reynolds numbers. The present study is investigated at static angles of attack ${\alpha}=0^{\circ},\;3^{\circ},\;6^{\circ}$ and $Re=2.3{\times}10^4,\;3.3{\times}10^4,\;4.8{\times}10^4$ by using a smoke-wire technique. The results of this study show that the laminar boundary layer on the airfoil surface is attached to the surface at ${\alpha}=0^{\circ}$, and that laminar separation of boundary layer on the airfoil surface occurs at ${\alpha}=3^{\circ}$. Furthermore, reattachment of the boundary layer occurs in the case of ${\alpha}=6^{\circ}$. In the current study, the location of the laminar separation point moves upstream as the Reynolds number and the angle of attack increase.

• 한국항공운항학회지
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• 제14권4호
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• pp.24-30
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• 2006

An experimental study was carried out in order to investigate the influence of boundary layer behavior on the near-wake at low Reynolds numbers. An X-type hot-film probe(55R51) was used to measure the near-wake of an NACA 0012 airfoil at static angles of attack ${\alpha}=0^{\circ}$, $3^{\circ}$, and $6^{\circ}$, and the Reynolds numbers Re=2.3${\times}10^4$, 3.3${\times}10^4$, and 4.8${\times}10^4$. The results of the study show that the characteristics of the boundary layer on the airfoil surface have a close relationship with the mean velocity and turbulence intensity profiles of a near-wake. Therefore, the development of the boundary layer, the position of the separation point, and the existence and non-existence of reattachment on the airfoil surface were represented by the differences in mean velocity and turbulence intensity profiles of the near-wake.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.64.1-64.1
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• 2011

Small horizontal axis wind turbines (HAWTs) can be used to produce power in areas where the wind conditions are not favorable or optimal for large HAWTs. A newly designed airfoil for use in small HAWTs was analyzed in CFD to predict the aerodynamic performance at various Reynolds numbers over a various angles of attack. The coefficient of lift and drag, CL and CD, and the pressure distribution over the airfoil was obtained. It was found that the airfoil could achieve very good aerodynamic characteristics. The results of the numerical analysis will be compared against experimental data for validation purposes.

• 대한기계학회논문집B
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• 제21권7호
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• pp.911-918
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• 1997

The turbulent viscous wake flows behind a single airfoil, two-dimensional stationary blade row and three-dimensional rotating blade row were calculated, and the numerical results were compared with experimental ones. The numerical technique was based on the SIMPLE algorithm using three turbulent closure models, standard k-.epsilon. model(WFM), low Reynolds number k-.epsilon. model(LRN) and Reynolds stress model (RSM). In the case of a single airfoil, WFM, LRN and RSM presented fairly good velocity distributions in the wake compared with experimental data. In the case of the stationary blade row, LRN and RSM presented better results than WFM for wake velocity distribution, and especially LRN showed best results among these three turbulent models. In the case of the rotating blade row, WFM and LRN showed fairly good agreement with experimental data of the three-dimensional velocity component distributions in the range from hub to mid span region. LRN was also superior to WFM in accuracy of prediction for the wake velocity distribution as same with the cases of a airfoil and the stationary blade row.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.354-357
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• 2008

Drag reduction is one of main concerns for commercial aircraft companies than ever because fuel price has been tripled in ten years. In this research, Natural Laminar Flow airfoil is designed and tested to reduce drag at cruise condition, $c_l$=0.3, Re=3.4${\times}$10$^6$ and M=0.6. NLF airfoil is characterized by delayed transition from laminar to turbulent flow, which comes from maintaining favorable pressure gradient to downstream. Transition is predicted by solving Boundary Layer equations in viscous boundary layer and by solving Euler Equation outside the boundary layer. Once boundary layer thickness and momentum thickness are obtained, $e^N$-method is used for transition point prediction. As results, KARI's NLF airfoil is designed and shows better characteristics than NLF-0115. The characteristics are tested and verified at low Reynolds numbers, but at high Reynolds numbers, laminar flow characteristics are not obtainable because of fully turbulent flow over airfoil surfaces. Precious experiences, however, relating NLF airfoil design, subsonic and transonic tests are acquired.

• 한국항공우주학회지
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• 제34권10호
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• pp.16-23
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• 2006

저 레이놀즈수에서 NACA 0012 에어포일의 경계층 거동에 관한 연구가 터빈 블레이드와 초소형 비행체에서 적용될 수 있는 경계층을 파악하기 위하여 수행되었다. 레이놀즈수 Re=$2.3{\times}10^4$, $3.3{\times}10^4$, $4.8{\times}10^4$과 정적 받음각 ${\alpha}$=$0^{\circ}$, $3^{\circ}$, $6^{\circ}$에서 경계층을 측정하기 위해 열선 풍속계가 사용되었다. 연구결과는 정적 받음각 =$0^{\circ}$에서는 층류 경계층이 에어포일 표면에 부착되며, 정적 받음각 $3^{\circ}$에서는 경계층 층류 분리가 발생된 것을 보여준다. 더욱이 본 연구에서 경계층 재부착 현상은 정적 받음각 $6^{\circ}$에서 레이놀즈수 $3.3{\times}10^4$와 $4.8{\times}10^4$에서 발생된다.

• 한국항공우주학회지
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• 제30권5호
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• pp.1-8
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• 2002

초소형 비행체(MAV) 프로펠러에서 깃 익형의 공기역학적 특성은 매우 중요한 사항이다. 이를 위해서 저레이놀즈수 익형의 성능예측에 층류에서 난류로의 천이과정을 포함하는 XFOIL을 이용하여 프로펠러 깃 익형 단면의 양력과 항력 분포를 해석하였다. 익형모델은 저레이놀즈수 프로펠러 익형에 주로 이용되는 ARA-D 6%을 선택하였다. 계산된 익형의 공력 변수들과 최소에너지손실 조건을 이용하여 시위길이와 피치각 분포를 변화시킴으로써 초소형비행체의 설계조건에 적합한 가장 효율적인 프로펠러 형상을 구하였고, 현재 운용중인 Black Widow의 프로펠러 형상과 같은 설계조건에서 비교하였다. 설계결과 초소형비행체의 프로펠러에 적합하게 제공될 수 있음을 확인하였다.