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비정렬 적응격자 기법을 이용한 HART Ⅱ 로터 BVI 예측 및 동체 영향 예측 연구
유동옥,권오준 한국항공우주학회 2011 한국항공우주학회 학술발표회 논문집 Vol.2011 No.4
본 연구에서는 비정렬 격자를 기반으로 한 유동해석 프로그램을 이용하여 HART II 로터 형상에 대한 비정상 점성 유동해석을 수행하였다. 블레이드-와류 간섭 현상을 효과적으로 포착하기 위해 적응 격자기법을 적용하였으며, 블레이드의 탄성 변형은 HART II 실험데이터를 이용하여 모사하였다. 단일 로터형상과 로터-동체 형상에 대한 해석 결과들을 비교함으로써 동체가 로터의 공력 특성 및 와류 구조에 미치는 영향을 분석하였다. 동체를 포함한 로터 트림 해석 후 블레이드 조종 피치각의 예측 정확도가 향상되었으며, 블레이드 공력 예측 정확도 역시 향상된 것을 확인할 수 있었다. 격자 적응이 진행됨에 따라 블레이드 수직력의 고주파 성분이 더욱 정확하게 예측되었으며, 반면 저주파 성분은 크게 변화하지 않는 것을 확인할 수 있었다. In the present study, viscous flow simulations of the HART II rotor were conducted using a flow solver based on unstructured meshes. To capture the blade-vortex interaction (BVI) phenomena efficiently, a series of solution-adaptive mesh refinements was carried out. The blade deformation was prescribed from the HART II test data. Calculations were made for two configurations, isolated rotor and rotor-fuselage configuration, to investigate the fuselage effect on the blade loading and the rotor wake structure. It was found that inclusion of fuselage makes significant improvement in the trim control prediction, and this improved trim control also leads to an improvement in the blade loading prediction for the rotor-fuselage configuration. It was also found that the high frequency blade loading caused by BVI can be obtained more accurately as the mesh is further refined, whereas the low one is mostly independent to the mesh resolution.
Passive Reduction of Pressure Fluctuation by Using Cylindrical Rod on Open Cavity
유동옥,김태욱,박수형,이승수,임진우,유흥철 한국항공우주학회 2022 International Journal of Aeronautical and Space Sc Vol.23 No.1
Wind tunnel experiments and numerical simulations were performed on the cavity over a fuselage of an aircraft to investigate the control effect of passive control devices on pressure fluctuations. The experiments were conducted in subsonic flow, and the control effects of each passive control shape were compared and analyzed. The results indicated that the spoiler- and rod-type devices affect the pressure fluctuation differently, and the reduction effect is excellent when using the cylindrical rod. The changes in the flow structure due to passive control devices were numerically analyzed using unsteady turbulent flow simulation based on the improved detached eddy simulation (IDDES) model. Conditions similar to those in the wind tunnel experiment were applied, and the distribution and trend of the overall sound pressure level were in good agreement with the numerical results. The control effect in the transonic flow was analyzed using a cylindrical rod designed for subsonic flow. The energy cascade of the flow is accelerated due to the passive control device that makes the free shear layer to be unstable. Thus, the feedback mechanism is weakened. And finally, the pressure fluctuation inside the cavity is reduced.
블레이드 요소 운동량 방법을 이용한 부유식 해상 풍력터빈의 로터 공력 예측
유동옥,김영진,권오준 한국항공우주학회 2014 한국항공우주학회 학술발표회 논문집 Vol.2014 No.11
본 연구에서는 블레이드 요소 운동량 방법을 이용하여 부유식 플랫폼 운동에 의해 발생하는 해상 풍력터빈 로터의 비정상 공력 특성을 예측하였다. 유동 박리와 후류 영향에 의한 비정상 공력 효과를 포착하기 위해 인디셜 응답 방법에 기반한 동적 실속 모델을 이용하였으며, 로터에 의해 유도되는 내리 흐름은 운동량 이론과 난류 후류 상태에 대한 경험적 모델을 연계하여 계산하였다. 공력 해석은 heave, sway, surge 방향으로의 병진 운동과 yaw, pitch, roll 방향으로 회전하는 NREL 5MW 풍력터빈을 대상으로 수행되었다. 해석 결과로부터, 세 방향 병진 운동 모드 중, surge 운동 시 로터 공력 변화가 상대적으로 크게 나타났으며, 회전 모드의 경우, pitch 운동에 의해 로터 공력이 크게 변화됨을 확인할 수 있었다. The effect of floating platform motions on unsteady rotor airloads of offshore wind turbines was investigated by using a blade-element momentum method (BEM). The unsteady airload effects due to the flow separation and the shed wake were considered by adopting a dynamic stall model based on the indicial response method. Rotor induced downwash was estimated using the momentum theory, coupled with empirical corrections for the turbulent wake states. The calculations were made for the NREL 5MW reference wind turbine undergoing three translations (heave, sway, and surge) and three rotations (yaw, pitch, and yaw). The results showed that among the translation modes, the surge motion has the largest influence on changing the rotor airloads, while the effect of pitch motion is predominant for the rotations.
레이저가공에서 나타나는 초음속제트의 사이거리 변화에 따른 충돌특성 연구
유동옥(DongOk Yu),이열(Yeol Lee) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
The characteristics of micro-sonic/supersonic jets impinging on a flat plate with a hole was numerically investigated, to observe the role of gas jet in the laser machining. For the various standoff distances between nozzle and plate, the characteristics of the mass flow rate through the hole and the jet flow's pressure loss were observed It was found that the present numerical results for the sonic jet impingement show a good agreement with the previous investigators' study, which reveals the accuracy of the present research. Further, the detailed impinging supersonic flow structures and the information of the mass flow rate through the hole were obtained for the various standoff distances. From this study, it was found that the mass flow rate through the hole was closely related with the total pressure loss caused by the Mach disc on the plate. Finally, a suggestion for the optimal design condition in the laser machining is proposed.
레이저가공에서 나타나는 초음속제트의 유동전압 변화에 따른 충돌특성 연구
유동옥(DongOk Yu),이열(Yeol Lee) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
Numerical study of the characteristics of micro-sonic/-supersonic jets impinging on a flat plate with a hole was performed, to investigate the role of gas jet to eject melted materials from the cut zone in the laser machining. The variation of the mass flow rate through the hole and the pressure loss of the jet flow were observed for the various total pressure of the jet flow. The present numerical results for the sonic jet impingement show a good agreement with the previous investigators' numerical and experimental results, which proves the accuracy of the present work. Further, for the supersonic nozzle flows, the detailed flow structure and the information of the mass flow rate through the hole were observed for various flow total pressures.
축적된 오염물에 의한 풍력터빈 블레이드 공력 성능 저하에 관한 수치적 연구
김영진,유동옥,권오준 한국항공우주학회 2014 한국항공우주학회 학술발표회 논문집 Vol.2014 No.11
본 연구에서는 비정렬 격자 기반의 유동해석 코드를 이용하여 NREL 5MW 풍력터빈 블레이드의 공력 해석을 수행하였으며, 블레이드 앞전에 축적된 오염물에 의해 발생하는 공력 성능 저하를 조사하였다. 오염물이 증착될 경우, 앞전 부근에서 유동 박리 현상이 발생하며, 이는 풍력터빈의 공력 성능 저하를 유발함을 확인하였다. 증착되는 오염물의 크기가 증가할수록 공력성능의 저하는 크게 나타나며, 풍력터빈이 날개 끝 속도비가 큰 낮은 풍속에서 운용될 때 공력성능이 저하됨을 확인하였다. In the present study, aerodynamic analyses of the NREL 5MW reference wind turbine blades were conducted by using an unstructured mesh flow solver, and the aerodynamic performance loss due to accumulated contaminant along the blade leading edge was investigated. It was found that due to the contaminant, flow separations occur near the leading edge, which results in a reduced aerodynamic performance. This effect is further magnified as the contaminant size becomes larger. It was also found that the performance loss is particularly significant when the turbine operates at low wind speeds where the tip speed ratio is relatively large.
세장비 인 초음속 공동유동에서 차원 효과로 인한 유동 진동 주파수 분석
김태욱(T.U. Kim),박수형(S.H. Park),이승수(S. Lee),유동옥(D.O. Yu),유흥철(H.C. You) 한국전산유체공학회 2018 한국전산유체공학회지 Vol.23 No.3
Unsteady turbulent flow simulations were performed to investigate flow oscillation frequency due to three dimensional effect in supersonic cavity flow of length-to-depth ratio of 3, width-to-depth ratio of 1 and Mach 1.5. Two- and three-dimensional unsteady simulations result were compared with experimental data and prediction from the Rossiter equation. Pressure oscillation in three-dimensional cavity and the corresponding frequency were well matched with the empirical data. The flow structure corresponding to each mode was investigated. The results show that two dimensional flow is in the wake mode and three-dimensional flow is mainly in the shear layer mode. The oscillation frequency spectrum clearly indicate the three-dimensional effect due to the sidewall.