• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.256-261
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• 2008

A CFD analysis of helicopter flowfield in forward flight is considered as non-trivial issue because of the complexity of vorticity-dominated flowfield. In this work, a study on the selection of the proper location for the installation of the Pitot probe is conducted using a CFD code which can deal with the interaction of rotor blade vortex and body. To describe the flow patterns for rotating rotor blades and body, the sliding mesh scheme is utilized. Pressure distributions and flow patterns are also analyzed to identify regions free from the interaction of body and wake induced from rotor blades.

• International Journal of Aeronautical and Space Sciences
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• 제7권2호
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• pp.110-120
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• 2006

There have been developed many structural and fluid rotorcraft analysis models in rotorcraft community, and also lots of investigations have been conducted to combine these two models. These investigations turn out to be good at predicting the airloads precisely, but they have not taken the blade nonlinear deflection into account. For this reason, the present paper adopts a sophisticated structural model which can describe three-dimensional nonlinear deflection of the blade. And it is combined with two types of aerodynamic model. First one is generalized Greenberg type of finite-time aerodynamic model, which is originally established for a fixed wing, but later modified to be suitable for coupled flap-lag-torsional aeroelastic analysis of the rotor blade. Second aerodynamic model is based on the unsteady source-doublet panel method coupled with a free wake model. The advantages of the present method are capabilities to consider thickness of the blade and more precise wake effects. Transient responses of the airloads and structural deflections in time domain are mainly analyzed in this paper.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 춘계 학술대회논문집
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• pp.8-13
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• 2007

Unsteady flow simulation for the tiltrotor Smart UAV configuration was performed to investigate the powered rotor wake effect on aerodynamic characteristics. Calculations were performed to simulate various flow conditions based on different flight modes including hover, conversion and cruise. Three-dimensional compressible Navier-Stokes equation code were used for flow calculation and Chimera grid technique overlapping individually generated grids was employed. A dynamic grid method was adopted in simulation of the rotating blades. Flow calculations were also conducted for the un-powered case. Aerodynamic interaction between the rotor and airframe was investigated comparing three data sets from the un-powered, powered, and isolated rotor cases.

• 한국항공우주학회지
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• 제33권2호
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• pp.11-21
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• 2005

3차원 비정렬 격자를 이용한 로터-동체 공력 상호작용에 대한 수치적 해석을 수행하였다. 로터와 동체간의 상대적인 운동을 모사하기 위하여 해석 유동장을 회전하는 부분과 정지된 부분으로 나누어 계산하였다. 블레이드 끝단에서 생성되는 끝단 와류를 포착하기 위하여 준 비정상 적응 격자 기법을 도입하였다. 또한 낮은 속도로 전진 비행하는 헬리콥터 해석을 위해서 저 마하수 예조건화 기법을 적용하였다. 로터-동체 공력 간섭현상에 대한 검증을 위해 Georgia Tech 형상과 NASA에서 실험한 ROBIN 형상에 대한 실험 결과와 비교하여 본 연구 해석 기법이 타당함을 보였다.

• 한국소음진동공학회논문집
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• 제16권3호
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• pp.291-297
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• 2006

The BVI(blade vortex interaction) noise Prediction has been one of the most challenging acoustic analyses in helicopter aeromechanical Phenomenon. It is well known high resolution airloads data with accurate tip vortex positions are necessary for the accurate prediction of this phenomenon. The truly unsteady time-marching free-wake method, which is able to capture the tip vortices instability in hover and axial flights, is expanded with the rotor flapping motion and trim routine to predict unsteady airloads in forward and descent flights. And Farassat formulation 1-A based on the FW-H equation is applied for the noise prediction considering the blade flapping motion. Main objective of this study is to validate the newly developed prediction code. To achieve the objective, the descent flight condition of AH-1 OLS(operational loads survey) configuration is analyzed using present code. The predicted sectional thrust distribution and sectional airloads time histories show the present scheme is able to capture well the unsteady airloads caused by a parallel BVI. Finally, the predicted noise data, observed in two different positions where are 3.44 times of rotor radius far from the hub center, are quite reasonable agreements with the experimental data compared to the other analysis results.

• 동력기계공학회지
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• 제9권1호
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• pp.23-29
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• 2005

Numerical analysis of three-dimensional viscous flow-fields in the turbine rotor passages was carried out to investigate flow physics including the interaction between secondary vortices, tip leakage vortex, and the rotor wake. The blade tip geometry was accurately modeled adopting the embedded H grid system. An explicit four-stage Runge-Kutta scheme was used for the time integration of both the mean flow and turbulence equations. The computational results for the entire turbine rotor flows, particularly the tip clearance flow and the secondary flows, were interpreted and compared with the experimental data from the Penn State turbine stage. The predictions for major features of the flow field have been found to be in good agreement with the experimental data.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 추계 학술대회논문집
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• pp.171-175
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• 2003

Numerical analysis of three-dimensional viscous flow-fields in the turbine rotor passages is carried out to investigate flow physics including the interaction between secondary vortices, tip leakage vortex, and the rotor wake. The blade tip geometry is accurately modeled adopting the embedded H grid topology. An explicit four-stage Runge-Kutta scheme is used for the time integration of both the mean flow and turbulence equations. The computational results for the entire turbine rotor flows, particularly the tip clearance flow and the secondary flows, are interpreted and compared with the experimental data from the Penn State turbine stage. Good agreement between the experimental data and the numerical prediction was achieved in the sense of the major features of the flow fields.

• 대한기계학회논문집B
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• 제25권3호
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• pp.330-338
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• 2001

This paper is concerned with the effect of cylinder wakes upstream on blade characteristics of compressor cascade(NCA 65 series). At first, it is found that the velocity defect ratio of cylinder wake varies according to the acceleration and deceleration in a flow field but, is conserved nearly constant at flow downstream the cascade, irrespective of the flow path in the cascade. When a cylinder wake flows along near the suction surface of the blade, or impinges on the leading edge, the turbulent velocities are supplied on or inside the outer edge of boundary layer near the leading edge of suction surface, and the transition to a transitional or turbulent boundary layers is induced, so that the laminar separation is prevented, but the profile loss increases. The transition of boundary layer to a transitional or turbulent one is strongly related with the strength of added turbulent velocities near the leading edge on the suction surface, which is influenced by the flow path of a cylinder wake.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.610-615
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• 2001

Effects of rotor-stator blade count ratio on the unsteady aerodynamic characteristics of a cascade was studied by using a Navier-Stokes code. Present Navier-Stokes code is a parallel code and works on a multi-cpu machine. It is based on the SIMPLE algorithm and uses QUICK scheme for convection terms and second order back difference for all temporal derivatives. Computations were carried out for two cases : case 1 is for 3 stator cascade passages subjected to two upstream wakes while case 2 is for 2 stator cascade passages subjected to three upstream wakes. Numerical solutions show that rotor-stator blade count ratio plays a significant role in the unsteady aerodynamic characteristics of the stator cascade. Case 2 shows smaller unsteady fluctuation than case 1, even if they show the same time averaged value. The smaller fluctuation of case 2 is believed due to strong interaction between unsteady vortices. The unsteady lift variation of case 2 is shown to have many high frequency fluctuations as more unsteady vortices travel around the cascade. The unsteady turbulent kinetic energy due to the upstream wake is also shown to decay faster through the cascade passage than in the free stream.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.661-667
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• 2001

This paper is concerned with the effects of periodically approaching upstream wakes on cascade-flow and loss. The reduced frequency of the periodic wakes was varied in the narrow range from 0.5 to 0.7. According to a wake-passing through the cascade, two velocity deficits appear near the boundary layer contour in the downstream from about 60% chord-length. The first velocity deficit is caused by a periodic wake and the second one appears after some delayed time. The second velocity deficit may be interpreted as the results of reattachment of flow-separation. The higher reduced frequency decreases the duration time of separation appearance and the lesser loss of aerofoil is resulted.