• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 Proceedings of 2004 Korea-Japan Joint Seminar on Particle Image Velocimetry
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• pp.15-23
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• 2004

The present study is aimed to achieve dynamic visualization from the in-house 3-D stereoscopic PIV to represent quantitative flow information such as time-resolved 3-D velocity distribution, vorticity, turbulent intensity or Reynolds stresses and so on. One of the application of the present study is Leading edge extension(LEX) flow appearing on modern delta wing aircraft. The other is mixing flow in stirring tank used in industry field. LEX in a highly swept shape applied to a delta wing features the modern air-fighters. The LEX vortices generated upon the upper surface of the wing at high angle of attack enhance the lift force of the delta wing by way of increased negative suction pressure over the surfaces. The present method resolves also the complicated flow patterns of two type impellers rotating in stirring vessel. Flow quantities such as three velocity vector components, vorticity and other flow information can be easily visualized via the 3D time-resolved post-processing visualization. And it makes the easy understanding of the unsteady flow characteristics of the typical industrial mixers.

• Advances in aircraft and spacecraft science
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• 제3권3호
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• pp.243-257
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• 2016

The increase of air traffic volume has brought an increasing amount of issues related to carbon and NOx emissions and noise pollution. Aircraft manufacturers are concentrating their efforts to develop technologies to increase aircraft efficiency and consequently to reduce pollutant discharge and noise emission. Ultra High By-Pass Ratio engine concepts provide reduction of fuel consumption and noise emission thanks to a decrease of the jet velocity exhausting from the engine nozzles. In order to keep same thrust, mass flow and therefore section of fan/nacelle diameter should be increased to compensate velocity reduction. Such feature will lead to close-coupled architectures for engine installation under the wing. A strong jet-wing interaction resulting in a change of turbulent mixing in the aeroacoustic field as well as noise enhancement due to reflection phenomena are therefore expected. On the other hand, pressure fluctuations on the wing as well as on the fuselage represent the forcing loads, which stress panels causing vibrations. Some of these vibrations are re-emitted in the aeroacoustic field as vibration noise, some of them are transmitted in the cockpit as interior noise. In the present work, the interaction between a jet and wing or fuselage is reproduced by a flat surface tangential to an incompressible jet at different radial distances from the nozzle axis. The change in the aerodynamic field due to the presence of the rigid plate was studied by hot wire anemometric measurements, which provided a characterization of mean and fluctuating velocity fields in the jet plume. Pressure fluctuations acting on the flat plate were studied by cavity-mounted microphones which provided point-wise measurements in stream-wise and spanwise directions. Statistical description of velocity and wall pressure fields are determined in terms of Fourier-domain quantities. Scaling laws for pressure auto-spectra and coherence functions are also presented.

• International Journal of Aeronautical and Space Sciences
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• 제18권3호
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• pp.474-484
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• 2017

This paper studies the applicability of an efficient numerical model based on artificial neural networks (ANNs) to predict the dynamic responses of the wing structure of an airplane due to atmospheric turbulence in the time domain. The turbulence velocity is given in the form of a stationary Gaussian random process with the von Karman power spectral density. The wing structure is modeled by a classical beam considering bending and torsional deformations. An unsteady vortex-lattice method is applied to estimate the aerodynamic pressure distribution on the wing surface. Initially, the trim condition is obtained, then structural dynamic responses are computed. The numerical solution of the wing structure's responses to a random turbulence profile is used as a training data for the ANN. The current ANN is a three-layer network with the output fed back to the input layer through delays. The results from this study have validated the proposed low-cost ANN model for the predictions of dynamic responses of wing structures due to atmospheric turbulence. The accuracy of the predicted results by the ANN was discussed. The paper indicated that predictions for the bending moments are more accurate than those for the torsional moments of the wing structure.

• 한국항공우주학회지
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• 제36권10호
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• pp.954-961
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• 2008

원형 손상구멍이 있는 날개 주위 유동장에 대한 실험연구를 수행하였다. 손상은 시위의 10% 직경의 시위에 수직인 원형 구멍으로, 구멍 중심은 1/4 시위 혹은 1/2 시위에 위치하고 있다. 입자영상유속계에 의한 유동장 측정과 날개의 아래 및 윗면에서의 정압장을 시위를 기준으로 한 레이놀즈수 Rec=2.85×105에서 측정하였다. 입자영상유속계에 의한 유동 측정 결과 손상 구멍 주위에는 두 가지 형태의 유동구조가 형성되었다. 하나는 약한 제트로 손상 구멍 하류에서 부착된 후류가 생성된다. 다른 하나는 받음각 증가에 의한 강한제트에 의한 것으로 손상구멍으로부터 자유흐름으로 관통되어 접근하는 경계층 흐름을 박리시켜 역류가 있는 박리 후류구조를 생성한다. 날개면 압력 자료는 원형 손상 구멍 근처에서 큰 압력변화를 보여주었다. 이러한 압력변화는 손상구멍이 앞전 쪽에 가까울수록 증가하였다.

• Smart Structures and Systems
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• 제3권1호
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• pp.89-114
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• 2007

Two aspects of the design of a small-scale smart wing are addressed in this work, related to the ability of the wing to modify its cross section assuming the shape of two different airfoils and to the possibility of deflecting the profiles near the trailing edge in order to obtain hingeless control surfaces. The actuation is provided by one-way shape memory alloy wires eventually coupled to springs, Shape Memory Alloys (SMAs) being among the most promising materials for this kind of applications. The points to be actuated along the profiles and the displacements to be imposed are selecetd so that they satisfactorily approximate the change from an airfoil to the other and to result in an adequate deflection of the control surface; the actuators and their performances are designed so that an adequate wing stiffness is guaranteed, in order to prevent excessive deformations and undesired airfoil shape variations due to aerodynamic loads. The effect of the pressure distributions, calculated by way of the XFOIL software, and of the actuators loads, is estimated by FE analyses of the loaded wing. Two prototypes are then realised incorporating the variable airfoil and the hingeless aileron features respectively, and the verification of their shapes in both the actuated and non-actuated states, supported by image analysis techniques, confirms that interesting results are achievable with the proposed lay out and design considerations.

• 한국해양공학회지
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• 제24권2호
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• pp.47-52
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• 2010

The proper surface pressure on the pistons rings in the diesel engine of a ship is very important, because the pressure controls the oil that is needed to maintain friction at acceptable levels between the pistons and the cylinders. In this paper, basic and theoretical concepts to compute the ring pressure were formulated and applied to obtain the proper surface pressures on selected sample piston rings. During the calculation of the pressure on the piston rings, the computation of the accurate free shape of the piston ring was required. Earlier, Arnold and Prescott introduced theories to compute the free shapes of piston rings, and their approach used rectangular and polar coordinates. In this paper, the free shapes of piston rings using two different theories were computed and compared. The results were quite close, representing the free shape of the piston ring. Ring pressure was computed using the Arnold's free shape that was obtained. A simple GUI was made to compute the surface pressure on the piston rings.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2000년도 Proceeding of CIN-KIN Joint Symposium 2000 on M.E.T. Under STCW 78/95 and SINO-KOREA MARITIME CONTACT IN MID-CENTURIES
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• pp.107-114
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• 2000

Marine analysis was made to investigate the hydrodynamic effects of a Wing in Ground (WIG) by means of finite difference techniques. The air flow field around WIG is analyzed by the Marker & Cell (MAC) based method, and the interaction between WIG and the free surface are studied by showing pressure distributions above the free surface. In the latter part, computations are extended to make clear the flow characteristics of a high speed catamaran in the rang of Froude numbers 0.2 to 1.0 with a separation to length ratios of 0.2, 0.3 and 0.5. The Navier-Stokes solver is invoked in which the nonlinear free-surface boundary condition is applied. For the validation, computational results are compared with the experiments.

• 대한조선학회논문집
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• 제31권1호
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• pp.84-93
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• 1994

본 연구에서는 NACA0012단면을 갖는 타원형날개끝 캐비테이션과 유기소음특성에 미치는 표면거칠기의 영향이 실험적으로 조사되었다. 사용한 표면거칠기는 조도 $200{\mu}m$의 입자로서, 날개끝 3cm 구간에 부착하였다. 또한 날개끝과 앞날에 각각 3cm의 거칠기를 준 경우도 별도로 조사되었다. 캐비테이션 발생시험 결과 캐비테이션 초기발생위치는 실험한 받음각 범위에서 날개끝으로부터 대략 1/2 코오드정도 후류이며, 캐비테이션 수가 감소함에 따라 변화하는 형상을 보였다. 날개끝 캐비테이션에 의한 소음은 주파수 3-50kHs사이의 비교적 고주파수에서 음압이 증가하는 양상을 보였으나, 더 낮은 캐비테이션수에서 날개 앞날 캐비테이션으로 확장되면 전 주파수 범위에 걸쳐서 소음이 증가하었다. 캐비테이션과 소음발생은 표면거칠기가 증가할때 개선되는 경향을 보였으나 그 차이는 크지않았다. 날개 앞날과 끝날에 거칠기를 준 경우가 낮은 캐비테이션수에서 다소 유리한 캐비테이션 특성을 보여준 반면 양력-항력비의 감소에 따른 문제점도 지적되었다.

• 대한조선학회논문집
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• 제30권1호
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• pp.94-103
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• 1993

NACA0020 단면을 갖는 타원형 날개끝에서 발생되어 전개되는 Tip Vortex를 연구하기 위하여 날개표면과 후류에서의 유동특성을 조사하였다. 날개표면 유동은 Tufts법과 캐비테이션 관찰로 분석되었으며 날개표면 압력계측으로 유동가시화 결과를 보완하였다. 연구결과 강력한 스팬방향 압력구배가 Tip Vortex 생성에 결정적 영향을 줌과 아울러 날개 양쪽면에서의 유동이 공히 보오텍스의 생성에 기여함을 알 수 있었다. 한편, 자세한 Tip Vortex의 구조를 보기위하여 캐비테이션 관찰, Laser Sheet 기법에 의한 보오텍스 단면가시화 및 유속계측이 실시되었는데 보오텍스의 형상과 강도는 날개의 받음각에 지배되어 나타났다. 날개끝 유동의 전반적인 특성은 비점성유동 가정하에서 사용되는 보오텍스 모델링을 보완할 목적으로 분석되었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1996년도 춘계 학술대회논문집
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• pp.85-92
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• 1996

Numerical simulations are made for the three-dimensional flow around a wing in ground effect craft haying the complex geometry. A numerical tool is developed for the primary design of hull and wing shape of practical Wing-In-Ground effect(WIG) stop. The finite-difference method is utilized to descretize the governing equations and pressure field is obtained by using Marker-And-Cell(MAC) method. The air and water flows are simultaneously simulated in the time-marching solution procedure for the Navier-Stokes equation. The porosity technique and the density function are devised for the implementation of the three-dimensional body-boundary and the free-surface conditions, respectively. In this paper, a craft is modeled simply by three blocks containing a wing mounted on a main body horizontally, with the endplate. The numerical calculations of a WIG advancing in a calm water are performed and the WIG-generated wave profiles are also obtained. In the final paper, details of the numerical methods employed for the present study and calculated results are discussed.