• 한국전산유체공학회지
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• 제21권3호
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• pp.48-54
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• 2016

In the present work, numerical simulations were conducted on the scaled model of the BWB type UCAV in the subsonic region using ANSYS FLUENT V15. The prediction method was validated through comparison with experimental results and the effect of the twisted wing was investigated. To consider the transitional flow phenomenon, ${\gamma}$ transition model based on SST model was adopted. The coefficients of lift, drag and pitching moment were compared with experimental results and the pressure distribution and streamlines were investigated. The twisted wing decreases the lift force but increases lift-to-drag ratio through delay of stall and leading edge vortex's movement to the front, also the non-linearity of the pitching moment is decreased.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.414-419
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• 2011

Missile am fighter aircraft have been challenged by low restoring nose-down pitching moment at high angle of attach. The consequence of weak nose-down pitching moment can be resulting in a deep stall condition. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance and safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed at high angle of attack up to 60 degrees around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.3 and Reynolds number of $10^5$. The lift, drag, pressure distribution, etc. are analyzed according to the angle of attack. The results at a low angle of attack are compared with other results before a stall condition. From a certain high angle of attack, the strong vortex formed by the leading edge are flowing downstream as like Karman vortex around a circular cylinder. Unsteady velocity field, periodic vortex shedding, the unsteady pressure distribution on the airfoil surface, and the acoustic fields are analyzed. The effects of these unsteady characteristics in the aerodynamic coefficients are analyzed.

• 한국전산유체공학회지
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• 제18권1호
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• pp.1-6
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• 2013

Missile and fighter aircraft have been challenged by low restoring nose-down pitching moment at high angle of attach. The consequence of weak nose-down pitching moment can be resulting in a deep stall condition. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance and safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed at high angle of attack up to 50 degrees around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.3 and Reynolds number of $10^5$. The lift, drag, pressure, entropy distribution, etc. are analyzed according to the angle of attack. The results of average lift coefficients are compared with other results according to the angle of attack. From a certain high angle of attack, the strong vortex formed by the leading edge are flowing downstream as like Karman vortex around a circular cylinder. The primary and secondary oscillating frequencies are analyzed by the effects of these unsteady aerodynamic characteristics.

• International Journal of Aeronautical and Space Sciences
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• 제16권1호
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• pp.8-18
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• 2015

A numerical simulation for a nonslender BWB UCAV configuration with a rounded leading edge and span of 1.0 m was performed to analyze its aerodynamic characteristics. Numerical results were compared with experimental data obtained at a free stream velocity of 50 m/s and at angles of attack from -4 to $26^{\circ}$. The Reynolds number, based on the mean chord length, is $1.25{\times}106$. 3D multi-block hexahedral grids are used to guarantee good grid quality and to efficiently resolve the boundary layer. Menter's shear stress transport model and two transition models (${\gamma}-Re_{\theta}$ model and ${\gamma}$ model) were used to assess the effect of the laminar/turbulent transition on the flow characteristics. Aerodynamic coefficients, such as drag, lift, and the pitching moment, were compared with experimental data. Drag and lift coefficients of the UCAV were predicted well while the pitching moment coefficient was underpredicted at high angles of attack and influenced strongly by the selected turbulent models. After assessing the pressure distribution, skin friction lines and velocity field around UCAV configuration, it was found that the transition effect should be considered in the prediction of aerodynamic characteristics of vortical flow fields.

• 한국항공우주학회지
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• 제32권5호
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• pp.10-17
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• 2004

본 연구에서는 헬리콥터의 전진비행성능 향상에 필수적인 로터블레이드의 동적실속성능을 향상시키기 위한 수동제어기법에 대한 연구를 수행하였다. 로터블레이드의 동적실속성능을 향상시키기 위해서는 블레이드 익형에 발생하는 유동박리에 대한 제어를 통해 양력 특성과 피칭모멘트 특성을 동시에 향상시켜야만 한다. 본 연구에서는 실제구현이 용이한 고정 앞전Droop과 Gurney 플랩을 심한 동적실속영역에 대해 동시에 적용하여 기존의 동적실속 제어기법에 비해서 탁월한 양력성능 향상 및 피칭 모멘트 성능 향상을 얻을 수 있음을 확인하였다.

• Interaction and multiscale mechanics
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• 제1권3호
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• pp.381-396
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• 2008

The aerostatic instability of cable-supported bridges is studied, with emphasis placed on modeling of the geometric nonlinear effects of various components of cable-supported bridges. Two-node catenary cable elements, which are more rational than truss elements, are adopted for simulating cables with large or small sags. Aerostatic loads are expressed in terms of the mean drag, lift and pitching moment coefficients. The geometric nonlinear analysis is performed with the dead loads and wind loads applied in two stages. The critical wind velocity for aerostatic instability is obtained as the condition when the pitching angle of the bridge deck becomes unbounded. Unlike those existing in the literature, each intermediate step of the incremental-iterative procedure is clearly given and interpreted. As such, the solutions obtained for the bridges are believed to be more rational than existing ones. Comparisons and discussions are given for the examples studied.

• 문화기술의 융합
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• 제9권6호
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• pp.941-946
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• 2023

미래 운송수단으로 거론되는 UAM을 중심으로 함께 주목받는 eVTOL 항공기의 양력과 항속속도 및 항속거리 증대를 위해 Tilt Rotor와 Tandem Wing 개념을 본 논문의 기체에 도입했다. 기체를 제작 및 비행 실험을 진행하여 비행 영상과 비행 로그를 확보했다. 비행 영상과 비행 로그를 분석한 결과 기체 모멘트가 과도하게 앞으로 쏠리는 현상이 발생했고 자세가 회복되지 않음을 파악했다. 이에 XFLR5에서 날개 붙임각과 면적을 변경하며 기체의 세로안정성을 확보하기 위한 최적의 피칭 모멘트 계수를 도출되도록 CATIA를 통해 설계된 기체를, XFLR5로 해석했다. 본 연구의 결과는 Tilt Rotor와 Tandem Wing이 적용된 기체가 안정적인 피칭 모멘트 계수를 가질 수 있도록 도움을 주며, 이를 통해 세로안정성을 더욱 향상할 수 있는 새로운 방안을 제시했다.

• 한국해양공학회지
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• 제10권3호
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• pp.125-137
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• 1996

Experimental wind tunnel tests have been attempted to investigate the aerodynamic characteristics of floating offshore structure using some types of scaled mldels. The static behaviors of lift, drag forces and pitching moment of its models are measured to exammine the relationship between wind loads and incidence angle, wind velocity, shape of models. The effect of solid ground has been obtained also.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 추계 학술대회논문집
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• pp.101-104
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• 2004

CFD simulation is peformed for 2D and 3D frisbees flying at 10m/s. For convenience of simulation, rotation of 3D model is not considered. CFD results show that pitching moment makes the nose down and holes at the leading and trailing edges improve the lift characteristics of the frisbee.

• International Journal of Aeronautical and Space Sciences
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• 제17권3호
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• pp.315-323
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• 2016

This paper deals with experimental investigation of active flow control via synthetic jets using an unmanned combat air vehicle (UCAV) planform. Fourteen arrays of synthetic jets, mounted along both leading edges, were fully or partially activated to increase aerodynamic efficiency and reduce pitch-up moment. The measurements were carried out using a six-component external balance, a pressure scanner, and tuft flow visualization. It was observed that aerodynamic efficiency (L/D) and pitching moment were clearly affected by the location of jets. In particular, inboard and outboard actuation could effectively increase L/D. Moreover, inboard actuation showed a reduction in the pitch-up, even more than that generated by the full actuation. These results suggest that inboard actuation not only effectively increases L/D but also reduces the pitch-up using only a few actuators.