• 대한기계학회논문집B
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• 제33권11호
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• pp.924-931
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• 2009

The two-dimensional turbulent flow around the horn-type rudder has been examined in the present study by using the commercial code FLUENT. The standard ${\kappa}-{\epsilon}$ model is used as a closure relationship. The geometry of horn rudder is based on the NACA 0020 airfoil. The simulations for various angle attack (${\alpha}$) and yaw angle(${\delta}$) are carried out. The effect of Reynolds number is also investigated in this study. The cavitation is more possible when the yaw angle is $6^{\circ}$ and it is more serious as Reynolds number increases.

• 한국항공우주학회지
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• 제46권1호
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• pp.1-9
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• 2018

람다 날개 형태의 무인전투기는 동체-날개 융합익의 형태를 띄고 있어 일반적인 항공기에 비해 상대적으로 항력이 작고 레이더 반사 면적이 작아 우수한 스텔스 성능을 갖는다. 그러나 앞전 후퇴각에 의해 생성되는 앞전 와류의 영향으로 특정 받음각에서 피칭모멘트가 급격히 증가하는 현상이 나타난다. 본 연구에서는 무미익 람다 날개 형상을 기반으로 한 UCAV 1303 모델을 사용하여 풍동시험과 전산해석을 수행하였다. 실험 풍속은 50 m/s, 받음각 범위는 $-4^{\circ}{\sim}28^{\circ}$ 으로 하였으며 전산해석 또한 실험 조건과 동일하게 연구를 수행하였다. 본 연구를 통해 UCAV의 날개 비틀림이 피칭모멘트의 안정성에 미치는 영향을 확인하였다. 그 결과 날개에 음의 비틀림 각을 적용하였을 때 날개 바깥쪽에서의 유동 박리가 지연되면서 Pitch-break가 발생하는 받음각이 증가하였고, 양의 비틀림 각을 적용하였을 때 Pitch-break가 발생하는 받음각이 감소하였지만 양항비가 증가하는 것을 확인하였다.

• 수산해양기술연구
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• 제42권3호
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• pp.169-178
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• 2006

This research aims at establishing the fundamental characteristics of the kite through the analysis of the flow field around various types of kites. The approach of this study were adopted for the analysis; visualization by CFD(computational fluid dynamics). Also, the lift/drag and PIV(particle image velocimetry) tests of kites had been performed in our previous finding. For this situation, models of canvas kite were designed by solidworks(design program) for the CFD test using the same conditions as in the lift/drag tests. And we utilized FloWorks as a CFD analysis program. The results obtained from the above approach are summarized as follows: According to comparison of the measured and analyzed results from mechanical tests, PIV and CFD test, the results of all test were similar. The numerical results of lift-coefficient and drag-coefficient were 5-20% less than those of the tests when attack angle is $10^{\circ},\;20^{\circ}\;and\;30^{\circ}$. In particular, it showed the 20% discrepancy at $40^{\circ}$. The numerical results of the ratio of drag and lift were 8-13% less than those of the tests at $10^{\circ}$ and 10% less than those of the tests at $20^{\circ},\;30^{\circ}\;and\;40^{\circ}$. Pressure distribution gradually became stable at $10^{\circ}$. In particular, the rectangular and triangular types had the centre of the high pressure field towards the leading edge and the inverted triangular type had it towards the trailing edge. The increase of the attack angle resulted in the eddy in order of the rectangular, triangular and inverted triangular type. The magnitude of the eddy followed the same order. The effect of edge-eddy was biggest in the triangular type followed by the rectangular and then the inverted triangular type. The action point of dynamic pressure as a function of the attack angle was close to the rear area of the model with the small attack angle, and with large attack angle, the action point was close to the front part of the model.

• 한국수자원학회논문집
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• 제34권6호
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• pp.753-761
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• 2001

본 논문에서는 교각주위에서의 국부세굴 방지를 위한 사석 크기 및 접근각도 영향계수를 결정하기 위한 실험을 실시하였으며, 실험결과에 기초하여 사석크기 결정 공식과 접근각도 영향계수를 제안하였다. 접근각도 영향계수는 교각의 장폭비에 따라 다른 값을 보이며 교각에서의 접근각도가 증가됨에 따라 영향계수가 증가하는 경향을 보인다. 본 연구에서는 90%, 92.86%, 95%의 개도비와 1∼4의 장폭비를 가진 교각과 00, 150, 300, 450 및 600의 접근각도에 따른 실험을 실시하여 교각주위에서 국부 세굴 방지를 위한 사석크기를 결정하는 1개의 공식을 제안하였다. 본 논문에서 제안된 사석보호공의 크기 결정공식을 사용하여 사석을 크기를 산정한 결과와 기존의 6개의 사석 보호공 공식을 비교한 결과, 본 공식을 사용한 결과는 Richardson 공시을 이용하여 산정한 사석크기와 비슷한 결과를 나타내었다. 교각설치지점에 대한 흐름의 접근각도 영향계수가 고려된 본 논문에서 제안된 사석보호공 공식은 향후 국내 하천에서의 국부세굴 방지를 위한 사석보호공 설계에 폭넓게 사용될 수 있을 것으로 판단된다.

• 한국항공우주학회지
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• 제34권5호
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• pp.1-11
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• 2006

본 연구에서는 연속적 블로잉 요소들의 변화가 낮은 레이놀즈 수를 가지는 유동장에서 NACA 0015 익형 주위의 유동제어 및 익형의 실속제어에 미치는 영향에 대하여 비정렬 격자계를 사용하는 수치적 기법을 이용하여 살펴보았다. 실속 이전의 받음각들에서 연속적 블로잉 요소들의 변화에 따른 공력계수 및 모멘트 계수의 변화를 통하여 각 요소들의 유동제어 효과를 살펴보았으며, 각 요소들의 변화에 따른 실속각의 변화를 통하여 실속제어 효과를 살펴보았다. 실속이전의 받음각에서 비교적 강한 세기의 블로잉을 수행하면 항력의 증가를 동반한 양력의 증가가 나타났다. 앞전부근에서의 적절한 세기의 연속적 블로잉은 실속이전의 각에서 양력의 증가를 나타내고, 실속제어 특성을 보였다. 블로잉 제트의 방향이 유동제어를 하지 않았을 때의 블로잉 슬롯 주변 유동의 방향과 일치하는 경우가 가장 좋은 유동제어 특성을 나타냄을 알 수 있었다.

• 항공우주시스템공학회지
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• 제7권3호
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• pp.1-6
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• 2013

Numerical optimization of two dimensional high lift configuration was performed with flow solver and optimization method based on RSM(Response Surface Model). Navier-Stokes solver with Spalart-Allmaras turbulence model was selected for the simulation of highly complex and separated flows on the flap. For the simultaneous optimization of both flap shape and setting (gap/overlap), 10 design variables (eight variables for flap shape variation and two variables for flap setting) were chosen. In order to generate the response surface model, 128 experimental points were selected for 10 design variables. The objective function considering maximum lift coefficient, lift to drag ratio and lift coefficient at specific angle of attack was selected to reduce flow separation on the flap surface. The present method was applied to two dimensional fowler flap in landing configuration. After applying the present method, it was shown that the optimized high lift configuration had less flow separation on the flap surface and lift to drag ratio was suppressed over entire angle of attack range.

• 대한조선학회논문집
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• 제48권3호
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• pp.233-237
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• 2011

In the present experiments, vortical structures behind the hydrofoil trailing edge are visualized and analyzed as an elementary study for propeller singing phenomena. Two sorts of hydrofoil are selected for the measurement of shedding vortices. One was KH45 hydrofoil section and the other is KH45 with the truncated trailing edge that is positioned at X/C = 0.9523(C=chord length). Assuming the Strouhal number of 0.23, the shedding frequencies of vortices are extracted by analyzing the boundary layer thickness and the flow speed. The frequency distribution of shedding vortices is obtained with the variation of angle-of-attack while the flow speed is fixed to 8m/s. The truncation of the trailing edge makes the frequency of shedding vortices about 120Hz lower than that of original trailing edge and makes the vorticity value higher than the original trailing edge.

• Wind and Structures
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• 제34권1호
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• pp.29-42
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• 2022

Following the BARC initiative, wind tunnel measurements have been performed on a 5:1 rectangular cylinder. Pressure distribution has been measured in several sections, checking the two-dimensionality of the flow around the model. Mean values compare well with previous data. These measurements have been processed using the standard Proper Orthogonal Decomposition (POD) and the snapshot POD to obtain phase-resolved cycles. This decomposition has been used to analyze the characteristics of the flow around the cylinder, in particular, the behavior of the recirculation bubble in the upper/lower surfaces. The effect of the angle of attack, the turbulence intensity and the Reynolds number has been studied. First and second modes extracted from POD have been found to be related to the reattachment of the flow in the upper surface. Increasing the angle of attack is related to a delay in the reattachment position, while an increase in turbulence intensity makes the reattachment point to move towards the windward face.

• 한국전산유체공학회지
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• 제13권4호
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• pp.66-71
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• 2008

This research computes the viscous flow field and aerodynamics around the model of a commercial passenger airplane, Boeing 747-400, which cruises in transonic speed. The configuration was realized through the reverse engineering based on the photo scanning measurement. In results, the pressure coefficients at the several wing section on the wing surface of the airplane was described and discussed to obtain the physical meaning. The lift coefficient increased almost linearly up to $17^{\circ}$. Here the maximum lift occurred at $18^{\circ}$ according to the angle of attack. And the minimum drag is expected at $-2^{\circ}$. The maximum lift coefficient occurred at the Mach number 0.89, and the drag coefficient rapidly increased after the Mach number of 0.92. Also shear-stress transport model predicts slightly lower aerodynamic coefficients than other models and Chen's model shows the highest aerodynamic values. The aerodynamic performance of the airplane elements was presented.

• 한국가시화정보학회지
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• 제17권2호
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• pp.25-31
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• 2019

A device that consists of an array of hydrofoils (called a vane deployer) is widely used in ocean engineering. In general, the vane deployer has to spread out efficiently, which is possible by enhancing the lift-to-drag ratio. In the present study, using a computational fluid dynamics, we investigate the effect of hydrofoil arrangement on the lift-to-drag ratio to establish the condition in which a reasonable level of constant lift-to-drag ratio is achieved in a wide range of angle of attack, to avoid a degradation of the hydrodynamic performance. First, the flow around two-dimensional hydrofoil array is examined by varying the size of hydrofoil components, gap between the hydrofoils, and arrangement type. As a result, we determine the optimized hydrofoil array configuration whose lift-to-drag ratio is nearly independent on the angle of attack. Finally, a three-dimensional simulation is performed for the optimized geometry to estimate the performance of actual vane deployer.