• 한국항공우주학회지
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• 제33권9호
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• pp.1-8
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• 2005

이차원 타원형 날개꼴에서 펄스제트 브로잉에 의한 박리 제어 효과에 대하여 연구하였다. 박리 유동의 능동제어기술 개발을 위하여 압축공기를 사용하는 연속제트/간헐제트 엑츄에이터를 설계제작하여 타원형 날개 풍동 실험 모델에 장착하였다. 아음속 유동에서 날개 주위 유동장의 PIV 측정과 유동의 가시화을 통하여 간헐제트 브로잉의 타원형 날개의 실속제어 효과와 실용성에 대해 실험연구를 수행하였다. PIV 실험 결과 제트 브로잉에 의해 난류 후류 영역과 박리 버블의 크기를 현저하게 감소시킴으로써 박리제어가 가능함을 보였다. 간헐제트는 연속제트보다 박리제어에 보다 효과적이었다. 간헐제트의 주파수를 증가시키면 보다 높은 받음각에 이르기까지 난류 박리 후류를 효과적으로 억제할 수 있었다.

• 한국항공우주학회지
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• 제34권8호
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• pp.8-15
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• 2006

고받음각의 NACA23012익형에 대하여 synthetic jet을 이용하여 박리 제어를 수행하였다. 단일 synthetic jet을 이용하여 익형에 발생하는 앞전 박리를 효과적으로 지연시킬 수 있고, 또한 실속 특성을 개선 할 수 있음을 확인하였다. 그때 발생하는 비정상 유동 특성을 파악하였다. 또한, 현실적으로 구현 가능한 jet 속도를 얻기 위하여 multi-array synthetic jet의 특성을 파악하였다. 그리고, 단일 위치에 장착된 synthetic jet을 이용하여 박리를 제어 하였을 경우 익형 윗면에 발생하는 작은 와동을 제거하기 위하여, multi-location synthetic jet을 이용하였다. 작은 와동을 제거하고 안정적인 유동을 확보하기 위하여, 높은 진동수의 synthetic jet을 이용하여 국부적으로 효과적인 박리 제어를 통한 익형 주변의 유동의 전체적 특성을 안정화 시킬 수 있음을 확인하였다. Multi-location synthetic jet의 phase 변화를 이용하여 multi-array/multi-location synthetic jet의 성능 및 특성을 향상 시킬 수 있음을 확인하였다.

• 한국군사과학기술학회지
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• 제11권2호
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• pp.144-151
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• 2008

An experimental study has been conducted to investigate the effects of circular damage hole on the characteristics of airfoil performance. The damage on a wing created from a hit by anti-air artillery was modeled as a circular hole. Force balance measurements and static pressure measurements on the wing surface were carried out for the cases of having damage holes of 10% chord size at quarter chord and/or half chord positions. All experiments were conducted at Reynolds number of $2.85\times10^5$ based on the chord length. The surface pressure data show big pressure alterations near the circular damage holes. This abnormal surface pressure distribution produces shear stress that could lead to the acceleration of the structural degradation of the wing around the circular damage hole. However, in spite of the existence of circular damage holes, the measured force data indicated the only a slight decrease in lift accompanied by increase in drag compared to the results of undamaged one. The influence of damage hole on the aerodynamic performance was increased as the location of damage moved to the leading edge. The effect on the control force was insignificant when the damaged size was not large.

• 대한기계학회논문집
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• 제19권2호
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• pp.495-508
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• 1995

The self-excited vibrations of airfoil is related to the classical flutter problems, and it has been studied as a system with linear stiffness and small damping. However, since the actual aircraft wing and the many mechanical elements of airfoil type have various design variables and parameters, some of these could have strong nonlinearities, and the nonlinearities could be unexpectedly strong as the parameters vary. This abrupt chaotic behavior undergoes ordered routes, and the behaviors after these routes are uncontrollable and unexpectable since it is extremely sensitive to initial conditions. In order to study the chaotic behavior of the system, three parameters are considered, i.e., free-stream velocity, elastic distance and zero-lift angle. If the chaotic parameter region can be identified from the mathematically modeled nonlinear differential equation system, the designs which avoid chaotic regions could be suggested. In this study, by using recently developed dynamically system methods, and chaotic regions on the parameter plane will be found and the safe design variables will be suggested.

• 한국전산유체공학회지
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• 제17권1호
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• pp.54-60
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• 2012

Transition prediction results are validated with experimental data obtained from a transonic wind tunnel for the KU109C airfoil. A Reynolds-Averaged Navier-Stokes code is simultaneously coupled with the transition transport model of Langtry and Menter and applied to the numerical prediction of aerodynamic performance of the KU109C airfoil. Drag coefficients from the experiment are better correlated to the numerical prediction results using a transition transport model rather than the fully turbulent simulation results. Maximum lift coefficient and drag divergence at the zero-lift condition with Mach number are investigated. Through the present validation procedure, the accuracy and usefulness of both the experiment and the numerical prediction are assessed.

• 대한기계학회논문집 C: 기술과 교육
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• 제2권1호
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• pp.39-46
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• 2014

이 연구에서는 탄성 플랩이 뒷전에 장착된 2차원 날개 단면의 공력 특성을 전산 해석하였다. EDISON_CFD는 날개 주위의 비압축성 난류 유동을 시뮬레이션 하기 위해 이용되었으며, MIDAS_IT는 전산 해석 결과로 얻어진 압력 하중 하에서 탄성 플랩의 변위를 구조해석 하기 위해 사용되었다. EDISON_CFD와 MIDAS_IT의 반복 계산 절차를 이용하여, 플랩의 변위가 수렴되면 해석을 종료하여, 날개 단면에 작용하는 공력을 분석하였다. 양항비의 추정 결과 일정 받음각 이내에서 플랩의 유리한 효과가 나타날 것으로 예상된다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.652-655
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• 2008

Despite of the laminar-turbulent transition region co-exist with fully turbulence region around the leading edge of an airfoil, still lots of researchers apply to fully turbulence models to predict aerodynamic characteristics. It is well known that fully turbulent model such as standard k-${\varepsilon}$ model couldn't predict the complex stall and the separation behavior on an airfoil accurately, it usually leads to over prediction of the aerodynamic characteristics such as lift and drag forces. So, we apply correlation based transition model to predict aerodynamic performance of the NREL (National Renewable Energy Laboratory) Phase IV wind turbine. And also, compare the computed results from transition model with experimental measurement and fully turbulence results. Results are presented for a range of wind speed, for a NREL Phase IV wind turbine rotor. Low speed shaft torque, power, root bending moment, aerodynamic coefficients of 2D airfoil and several flow field figures results included in this study. As a result, the low speed shaft torque predicted by transitional turbulence model is very good agree with the experimental measurement in whole operating conditions but fully turbulent model(k-${\varepsilon}$) over predict the shaft torque after 7m/s. Root bending moment is also good agreement between the prediction and experiments for most of the operating conditions, especially with the transition model.

• 한국항공우주학회지
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• 제32권7호
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• pp.13-18
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• 2004

이 논문은 최적설계 기법의 적용을 통하여 전진비행하는 조건에서 헬리콥터 로터를 구성하는 에어포일의 공력성능을 향상시키는 것에 목적을 가지고 있다. 전진비행하는 로터의 유동장을 모사하는 에어포일의 동적반응에 의한 공력성능은 Navier-Stokes 방정식을 이용하여 계산되어진다. 최적설계 기법은 수리통계적인 방법에 기초하는 반응표면법과 적절한 목적함수와 제약조건의 조합을 통하여 최적점을 구해내는 유전 알고리즘으로 구성되어진다. 유동해석 방법과 설계기법의 통합을 바탕으로 공력성능이 향상된 에어포일의 형상을 구할 수 있었으며 통계학적인 방법에 기초하여 설계연구에 사용되어진 형상변수들이 공력성능에 영향을 미치는 정도를 파악할 수 있었다.

• Wind and Structures
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• 제22권5호
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• pp.595-616
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• 2016

Providing high starting torque and efficiency simultaneously is a significant challenge for vertical axis wind turbines (VAWTs). In this paper, a new approach is studied in order to modify VAWTs performance and cogging torque. In this approach, J-shaped profiles are exploited in the structure of blades by means of eliminating the pressure side of airfoil from the maximum thickness toward the trailing edge. This new profile is a new type of VAWT airfoil using the lift and drag forces, thereby yielding a better performance at low TSRs. To simulate the fluid flow of the VAWT along with J-shaped profiles originated from NACA0018 and NACA0030, a two-dimensional computational analysis is conducted. The Reynolds Averaged Navier-Stokes (RANS) equations are closed using the two-equation Shear Stress Transport (SST) turbulence model. The main objective of the study is to investigate the effects of J-shaped straight blade thickness on the performance characteristics of VAWT. The results obtained indicate that opting for the higher thickness in J-shaped profiles for the blade sections leads the performance and cogging torque of VAWT to enhance dramatically.

• 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.