• Structural Engineering and Mechanics
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• 제30권1호
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• pp.67-76
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• 2008

Limit cycle oscillations of a two-dimensional airfoil with quadratic and cubic pitching nonlinearities are investigated. The equivalent stiffness of the pitching stiffness is obtained by combining the linearization and harmonic balance method. With the equivalent stiffness, the equivalent linearization method for nonlinear flutter analysis is generalized to address aeroelastic system with quadratic nonlinearity. Numerical example shows that good approximation of the limit cycle can be obtained by the generalized method. Furthermore, the proposed method is capable of revealing the unsymmetry of the limit cycle; however the ordinary equivalent linearization method fails to do so.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.75-76
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• 2003

Direct numerical simulation results of aeolian tones generated by a two-dimensional obstacle (circular cylinder, square cylinder, NACA0012 airfoil) in a uniform flow are presented and the generation and propagation mechanisms of the sound are discussed. The unsteady compressible Navier-Stokes equations are solved by a highly-accurate finite difference scheme over the entire region from near to far fields. The direct numerical simulation results are also compared with the results obtained by Curle's acoustic analogy.

• Wind and Structures
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• 제5권2_3_4호
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• pp.245-256
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• 2002

Two-dimensional formulations for wind forces on elongated bodies, such as bridge decks, are reviewed and links with expressions found in two-dimensional airfoil theory are pointed out. The present research focus on indicial lift responses and admittance functions which are commonly used to improve buffeting analysis of bluff bodies. A computational fluid dynamic (CFD) analysis is used to derive these aerodynamic functions for various sections. The numerical procedure is presented and results are discussed which demonstrate that the particular shapes of these functions are strongly dependent on the evolution of the separated flows around the sections at the early stages.

• 한국항공우주학회지
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• 제37권2호
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• pp.121-130
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• 2009

전진 비행중인 자동회전 로터에 대한 비정상 수치해석 기법이 개발되었다. 자동회전 로터의 플래핑과 회전운동 방정식은 주어지는 시간간격에 따라 연속적으로 적분되며 이 때 회전면에서의 유도 속도장은 동적 유도흐름 이론(dynamic inflow theory)에 의해 계속 업데이트 되면서 블레이드의 모든 요소에서 유효 받음각을 결정하여 비정상 상태를 모사한다. 로터의 임의의 초기 회전속도 및 플래핑각에서 정상상태로 천이(transition)되는 과정을 시뮬레이션 하였고 블레이드 에어포일 공력 데이터들을 이용하여 방정식들의 수치해인 자동회전의 정상상태를 예측하였다. 2차원 Navier-Stokes 솔버로 받음각과 레이놀즈수에 따라 해석된 에어포일 데이터를 이용하여 자동회전의 비정상 시뮬레이션을 수행한 해석 결과는 풍동실험 결과와 잘 일치하였다

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2001년도 춘계 학술대회논문집
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• pp.51-59
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• 2001

An evaluation of one zero-equation and two one-equation eddy viscosity-transport turbulence closure models as implemented CFDS(Characteristic Flux Difference Splitting ) code is presented herein. Comparisons of Baldwin-Lomax model as zero-equation and Baldwin-Barth and Spalart-Allmaras model as one-equation are presented for three test cases, first inlvolving the 3 dimensional supersonic flow at M=1.98 over tangent ogive cylinder, second involving the 2 dimensional transonic flow at M=0.79 over RAE 2822 airfoil, third involving the 3 dimensional transonic flow at M=0.84 over ONERA M6 wing. The numerical results of CFDS code will also examined through direct comparison with experimental data.

• Advances in aircraft and spacecraft science
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• 제2권1호
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• pp.77-94
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• 2015

The paper focuses on the integration of a non-linear one-dimensional model of Synthetic Jet (SJ) actuator in a well-assessed numerical simulation method for turbulent compressible flows. The computational approach is intended to the implementation of a numerical tool suited for flow control simulations with affordable CPU resources. A strong compromise is sought between the use of boundary conditions or zero-dimensional models and the full simulation of the actuator cavity, in view of long-term simulation with multiple synthetic jet actuators. The model is integrated in a multi-domain numerical procedure where the controlled flow field is simulated by a standard CFD method for compressible RANS equations, while flow inside the actuator is reduced to a one-dimensional duct flow with a moving piston. The non-linear matching between the two systems, which ensures conservation of the mass, momentum and energy is explained. The numerical method is successfully tested against three typical test cases: the jet in quiescent air, the SJ in cross flow and the flow control on the NACA0015 airfoil.

• 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.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1998년도 유체기계 연구개발 발표회 논문집
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• pp.64-69
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• 1998

In this study, a preliminary design method of the axial fan was systematically established based on the two-dimensional cascade theory. Flow deviation, lift coefficient, distribution of velocity and pressure coefficient on blade surfaces were predicted by an inviscid theory of Martensen method, which was also applied to select an airfoil of required performance in the present design process. The aerodynamic performance of designed blades can be predicted quickly and reasonably by using the through-flow calculation method in the preliminary design process. It would be recommendable to adopt three-dimensional viscous flow calculation at the final design refinement stage.

• 한국유체기계학회 논문집
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• 제2권1호
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• pp.22-28
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• 1999

In this study, a preliminary design method of the axial fan was systematically established based on the two-dimensional cascade theory. Flow deviation, lift coefficient, distribution of velocity and pressure coefficient on blade surfaces were predicted by an inviscid flow theory of Martensen method, which was also applied to select an airfoil for required performance in the present design process. The aerodynamic performance of designed blades can be predicted quickly and reasonably by using the through-flow calculation method in the preliminary design process. It would be recommendable to adopt three-dimensional viscous flow calculation at the final design refinement stage.

• 한국소음진동공학회논문집
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• 제16권3호
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• pp.263-269
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• 2006

The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipolar broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and the full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to turbulence-cascade interaction.