• 한국가시화정보학회지
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• 제8권2호
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• pp.23-30
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• 2010

Regarding the aircrafts with a rotor blade system, the miniaturization of them is limited due to the rotor blade length and the tail rotor system. To miniaturize an aircraft, an equipment is required that increases thrust and also shortens the length of the rotor blade. The present study will conduct the flow analysis for miniaturizing the aircraft by applying a duct to the coaxial rotor blade system without tail rotor. First, the verification on the calculated results was conducted through the computational flow analysis on the coaxial rotor blade system without a duct. Then, the flow analysis for the coaxial rotor blade systems was performed including Ka-60 duct, Single duct, Twin duct, and Double duct, respectively. From the numerical results, the thrust coefficient appeared higher with the duct than without a duct for the coaxial rotor blade system. Especially, in the case of Double duct, the thrust was improved due to the increase of incoming flow and the extension of the wake area. These results will be used as the basic concepts for miniaturizing the aircraft with the rotor blade system. The flow analysis on the coaxial rotor blade system including the fuselage remains as a future work.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.153-156
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• 2006

A turbine stage consists of a stator and rotor. A stator provides the required inlet flow conditions so that a rotor can produce the necessary power. Passing wakes generated at the trailing edge of a stator make an interaction with a rotor. In the present study, this interaction flow mechanism is investigated using the numerical analysis. In case of the large gap distance between the stator and rotor, the stator and rotor flow analysis can be separated. First, only the stator flow field is solved. Second, the rotor flow field is solved including the passing wake information from the stator analysis. The passing wake experiences the shearing as it approaches to the rotor leading edge. And it is chopped when it strikes the rotor body. After that, the chopped wakes becomes the prolongation as it goes downstream. Also, the aerodynamic characteristics with the variation of the gap distance between a stator and rotor was investigated. Pressure jumps due to the passing wakes result in the pressure and lift loss and it gets stronger with the closer gap distance. This unsteady effect proves to be directly related to the fatigue and noise in turbomachinery and this study would be helpful to investigate such fields.

• 한국가시화정보학회지
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• 제9권2호
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• pp.40-47
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• 2011

Tilt-rotor aircraft can be used in various fields because they have the capabilities of the vertical take-off and landing and the high-speed cruise flight. In the present study, the flow analysis of a tilt-rotor aircraft is conducted at various tilt angles. The lift and drag forces of the tilt-rotor aircraft are obtained and the wakes by the rotor-blade are visualized. The result shows that the rotor-blade affects the lift force in a hovering mode and the main wing has an influence on the lift force in a cruise mode. Additional thrust is required at the tilt angle of around 40 degree due to the least lift force. The drag force is dependent on the rotor-blade at overall tilt angles. The minus drag force appears between the tilt angles of 90 degree and 55 degree. Also, the drag force is dramatically increased at the other tilt angles. The wake by rotor-blade affects the flow around the fuselage of the tilt-rotor aircraft at the tilt angles of 75 degree and 60 degree.

• 한국유체기계학회 논문집
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• 제18권6호
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• pp.37-44
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• 2015

Conjugate heat analysis on a high pressure turbine stage including secondary flow paths has been carried out. The secondary flow paths were designed to be located in front of the nozzle and between the nozzle and rotor domains. Thermal boundary conditions such as empirical based temperature or heat transfer coefficient were specified at nozzle and rotor solid domains. To create heat transfer interface between the nozzle solid domain and the rotor fluid domain, frozen rotor with automatic pitch control was used assuming that there is little temperature variation along the circumferential direction at the nozzle solid and rotor fluid domain interface. The simulation results showed that secondary flow injected from the secondary flow path not only prevents main flow from penetrating into the secondary flow path, but also effectively cools down the nozzle and rotor surfaces. Also thermal barrier coating with different thickness was numerically implemented on the nozzle surface. The thermal barrier coating further reduces temperature gradient over the entire nozzle surface as well as the overall temperature level.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1998년도 제10회 학술강연회논문집
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• pp.13-13
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• 1998

A simple model of the tip leakage flow models of the rotor downstream flow is developed, based on Lakshminarayana's theoretical concept on the tip clearance flow and the experimental data published in open literature. And new spanwise distribution models of deviation angle and pressure loss coefficient due to the tip leakage flow are formulated for use in association with the streamline curvature method as a through flow analysis. Combining these new models and previous deviation and loss models due to secondary flow, a robust streamline curvature method is established for flow analysis of single-stage, subsonic axial turbines with wide ranges of turning angle, aspect ratio and blading type. At the exit from rotor rows, the flow variables are mixed radially according to a spanwise transport equation. The proposed streamline curvature method is tested against a forced vortex type turbine as well as a free vortex type one. The results show that the spanwise variations of flow angle, axial velocity and loss coefficients at rotor exit are predicted with good accuracy, being comparable to a steady three-dimensional Navier-Stokes analysis. This simple and fast flow analysis is found to be very useful for the turbine design at the initial design phase.

• 한국해양공학회지
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• 제35권3호
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• pp.229-237
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• 2021

A numerical hydrodynamic performance analysis of the pitch-type multibody wave energy converter (WEC) is carried out based on both linear potential flow theory and computational fluid dynamics (CFD) in the unidirectional wave condition. In the present study, Salter's duck (rotor) is chosen for the analysis. The basic concept of the WEC rotor, which nods when the pressure-induced motions are in phase, is that it converts the kinetic and potential energies of the wave into rotational mechanical energy with the proper power-take-off system. This energy is converted to useful electric energy. The analysis is carried out using three WEC rotors. A multibody analysis using linear potential flow theory is performed using WAMIT (three-dimensional diffraction/radiation potential analysis program), and a CFD analysis is performed by placing three WEC rotors in a numerical wave tank. In particular, the spacing between the three rotors is set to 0.8, 1, and 1.2 times the rotor width, and the hydrodynamic interaction between adjacent rotors is checked. Finally, it is confirmed that the dynamic performance of the rotors slightly changes, but the difference due to the spacing is not noticeable. In addition, the CFD analysis shows a lateral flow phenomenon that cannot be confirmed by linear potential theory, and it is confirmed that the CFD analysis is necessary for the motion analysis of the rotor.

• 한국유체기계학회 논문집
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• 제7권6호
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• pp.15-20
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• 2004

Numerical analysis of the partial admission turbine in the KARI turbopump has been performed. Flow field of the partial admission turbine is intrinsically unsteady and three dimensional. To avoid heavy computational efforts, the frozen rotor method is adopted in computation and compared with the mixing plane approach. The frozen rotor method can represent the variation of a flow field along the circumferential direction of rotor blades, which have the different relative positions to the nozzle with one another. It also illustrates the wake loss mechanism starting from the lip of a nozzle, which is not captured in the mixing plane method. The frozen rotor method has proven to be an efficient tool for the design of a partial admission turbine.

• 한국항공우주학회지
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• 제35권4호
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• pp.275-280
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• 2007

터빈스테이지는 정익과 동익으로 구성되어 있다. 정익은 동익이 필요한 축 파워를 내도록 입구조건을 만들어준다. 정익 끝단에서 발생된 후류는 동익과 간섭을 일으킨다. 본 연구에서는 이러한 정익 동익간의 간섭현상을 고찰하였다. 정익과 동익의 간격이 큰 경우, 유동해석은 독립적으로 수행 될 수 있다. 정익 주위의 유동을 해석한 후, 발생되는 후류특성을 계산하여 동익의 유동해석에 포함시키었다. 정익에서 발생된 후류는 동익에 접근함에 따라 구부러지고 절단되며 흐름방향으로 연장되는 특성을 가지고 있다. 또한 정익과 동익 간격 영향을 고찰하였으며 그 간격이 가까울수록 후류의 압력 피크로 인한 압력 및 양력손실이 커짐을 알 수 있다.

• 동력기계공학회지
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• 제21권5호
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• pp.20-28
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• 2017

The steady-state, incompressible and three-dimensional numerical analysis was performed to investigate the flow fields around the seabed tiller used for soil improvement in coastal fisheries and the pulling force and buoyancy generated by tiller operation. The turbulence model used in this study is a realizable $k-{\varepsilon}$. As a results, at a stationary current or a current speed of 1.2 knots, where rotor rotates in a clockwise direction, a typical vortex pair appears near the tip of the rotor except for the edge, and the strength of the vortex pair increases with the number of revolutions of the rotor. The pulling force of the tiller rotating in the counterclockwise direction increases with the number of revolutions. Also, when the current flows at 1.2 knots and the rotor rotates clockwise, the pulling force of the tiller acts on the upstream side irrespective of the number of rotations of the rotor, so that no force is applied. The buoyancy of the tiller acts on the seawater surface if the flow direction inside the rotor is the same as the direction of rotation of the rotor, regardless of the current velocity, otherwise it acts on the seabed.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.160-163
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• 2010

부분흡입형 초음속 터빈의 노즐과 1단 로터 사이의 축방향 간극이 터빈의 단 성능과 유동장에 어떤 영향을 미치는지 알아보기 위해 터빈에 대한 3차원 유동해석을 수행하고 그 결과를 분석하였다. 상용 유동해석 프로그램 $FLUENT^{TM}$를 사용하였으며 다섯 가지 경우의 축간극에 대해 계산을 하였다. 노즐-로터 축간극이 팁 누설 유량의 증가와 로터 출구의 유동각에 영향을 주는 것을 확인하였다.