• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.411-414
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• 2006

풍력 발전기의 블레이드는 다른 회전기와는 달리 항상 지면의 경계층, 요-에러에 의한 어긋난 유입류, 타워와의 간섭효과의 환경에서 운영된다. 따라서 정상운전상태에서도 이와 같은 환경에서 겪게 되는 공력하중의 해석이 블레이드의 설계에서 중요하게 요구된다. 본 연구에서는 이의 비정상 공력하중해석을 위하여 자유후류기법을 이용한 방법을 연구하였다. 특히, 타워와의 간섭해석을 위하여 FVE라 명명한 후류 모델을 개발하여 적용하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.4
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• pp.275-280
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• 2007

A turbine stage consists of stators and rotors. The stator provides the required inlet flow conditions so that the rotor can produce the necessary power. Passing wakes generated from the trailing edge of the stator make an interaction with the rotor. In the present study, this flow mechanism is investigated using the numerical analysis. In case of a large gap distance between the stator and rotor, the flow can be solved independently. First, only the stator flow field is solved. Second, the rotor flow field is solved including the passing wake characteristics obtained from the stator analysis. The passing wake experiences the shearing as it approaches to the rotor blade leading edge. And it is chopped when it strikes the rotor blade. After that, the chopped wakes becomes the prolongation as it travels downstream. The flow according to the variation of the gap distance is also studied. Pressure jumps due to the passing wakes result in the pressure and lift loss and it gets stronger with the closer gap distance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.7
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• pp.709-715
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• 2011

In order to observe the wake interaction between tip vortices generated by a two-bladed rotor with slightly different pitch angles, the velocity components of the tip vortices were measured by using a two-dimensional LDV system. It was observed that the swirl velocity components of the ensuing blade deviated from the Vatistas' n = 2 vortex model and the axial velocity components of the preceding blade deviated from the Gaussian profile. It was also found that in the wake-age range of $200^{\circ}$ to $240^{\circ}$, the filament of the ensuing blade tip vortex was stretched as result of the closing in of two vortices. The results from these observations suggest the possibility that a similar wake interaction is generated in actual rotor blades, especially, in the ones with articulated hubs.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.3
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• pp.211-217
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• 2014

This study analyzes the nonlinear interaction between two different vortex shedding frequencies from a cylinder with two diameters. In particular, two different vortex shedding frequencies are generated by preparing a cylinder having two diameters artificially. Flow velocity fluctuations behind the cylinder are measured three-dimensionally. Additionally, we fabricated a hole and placed a pressure transducer for measuring the pressure on the cylinder surface. The pressure signal from the pressure transducer is used as basic signal. A TSC(Trans Spectrum Coherence) is used for checking the strength of the nonlinear interaction between two different vortex shedding frequencies. As a result, the following are clarified: i) frequency distribution behind the cylinder, ii) three-dimensional flow state behind the cylinder through calculation of ensemble average, and iii) close relationship between the vertical vortex and change of low frequency by nonlinear interaction between two different vortex shedding frequencies from the cylinder with two diameters.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.3
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• pp.211-219
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• 2008

A three-dimensional inviscid flow solver has been developed based on unstructured meshes for the investigation of the effect of the external stores on the tail surfaces of a generic fighter aircraft. The numerical method is based on a vertex-centered finite-volume discretization and an implicit point Gauss-Seidel time integration. The calculations were made for a steady flow and the computed results were compared with experimental data to validate the flow solver. An unsteady time-accurate computation of the generic fighter aircraft with external stores at transonic flight conditions showed that the external stores cause unsteady loading on the horizontal tail surface due to the mutual interference between their wake and the horizontal tail surface. It was shown that downward deflection of the trailing edge flap significantly reduces the undesirable interference effect.

• Proceeding of EDISON Challenge
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• 2012.04a
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• pp.33-36
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• 2012

풍력발전기 성능은 유동의 안정성과 풍속에 의해 결정되는데, 이때 유동 불안정성은 풍력발전기의 성능뿐만 아니라 구조적 문제를 함께 유발시킨다. 본 연구에서는 풍력발전기 타워 후류에서의 불안정성을 최소화시키기 위하여 타워 단면의 기초 형상설계 연구를 수행하였다. 기존의 풍력발전기 타워 형상에 부가 구조물을 설치함으로써 Karman vortex의 생성을 지연시키고 와류 간섭현상을 줄여 풍력발전기의 안정성을 증대시키고자 하였다. 이를 위해 다양한 타워 단면 형상에 대하여 양력계수 및 항력계수를 비교 분석하였다. 그 결과 반지름의 1/2 길이의 자유류 방향 tip과 splitter plate를 후방에 설치하는 것이 후류 불안정성을 억제하는데 가장 효율적인 것으로 나타났다.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.382-386
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• 2013

본 연구에서는 Main Rotor Blade Tip 형상 변화에 따른 후류해석을 통해 와류 생성 및 주변 유동을 분석하여 블레이드 팁 형상의 변화가 와류 간섭을 감소시키는지의 여부를 확인하였다. EDISON CFD를 이용하여 블레이드 Blade Tip 형상에 따라 유동이 어떻게 나타나며, Blade 후류의 압력과 점성의 변화를 분석하여 와류의 양상을 해석하였다. 비교 Blade 형상은 2세대 긴 직사각형 모형, KUH 수리온의 Blade, 유로콥터사의 'Blue Edge'로 비교적 최근에 개발된 대표적인 Blade Tip 형상 3개로 정하였다. 결과를 토대로 블레이드 뒷전의 와류흐름 양상을 확인하여 블레이드 와류 간섭현상의 감소를 확인하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.7
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• pp.615-626
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• 2009

The objective of this study is to investigate the interference effects due to tandem rotor's overlap in the forward flight. To resolve the instabilities caused by close proximity of the wake to the blade surface, the field velocity approach is implemented to the existing unsteady panel code coupled with a time-marching free wake model. The modified code is then used to investigate the effects of the selected parameters on the forward flight performance of the tandem rotor. The calculated results for rotor separation effect indicate that stagger(d/D) appears to have little effects on the forward flight performance at high advance ratio and the square of gap(H/D) is inversely proportional to overlap induced power factor. In addition, it is also shown that the overlap induced power factor increases to a certain extent and decrease back as the advance ratio increases.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.2
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• pp.123-132
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• 2015

In this study, an arrangement design process for multiple wind turbines, placed on the 10MW class floating wave-offshore wind hybrid power generation system, was presented, and the aerodynamic performance was evaluated by using a computational fluid dynamics. An arrangement design, which produces a maximum power in the site wind field, was found by using a commercial program, WindPRO, based on a blade element momentum theory, then the effect of wake interference on the system between multiple wind turbines was studied and evaluated by using ANSYS CFX.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.4
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• pp.329-335
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• 2009

The unsteady panel and time-marching free wake are applied to the rotor aerodynamics and wake behaviour. Numerical results of panel and free wake are compared and validated with experimental data. Using these methods, unsteady rotor aerodynamics in BVI condition is analyzed and discussed in detail.