• 한국군사과학기술학회지
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• 제26권2호
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• pp.149-158
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• 2023

To predict the aerodynamic characteristics of the grid fins from subsonic to supersonic speeds, low fidelity SW as well as CFD SW were applied. VLM(Vortex Lattice Method) and SE(Shock-Expansion) method were used at subsonic and supersonic speed domain respectively for the rapid prediction of low fidelity SW. For 2 configurations of the grid fins, the CFD computations and tests using the trisonic wind tunnel were also performed to compare the results of the grid fins. The results of low fidelity SW, CFD SW and the wind tunnel tests data were agreed well each other. Through further research on the grid fins, the effective parameters of the grid fin configurations according to the speed regime will be investigated.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.59.2-59.2
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• 2011

Although there are many activities on the construction of wind farm to produce amount of power from the wind, in practice power productions are not as much as its expected capabilities. This is because a lack of both the prediction of wind resources and the aerodynamic analysis on turbines with far wake effects. In far wake region, there are velocity deficits and increases of the turbulence intensity which lead to the power losses of the next turbine and the increases of dynamic loadings which could reduce system's life. The analysis on power losses and the increases of fatigue loadings in the wind farm is needed to prevent these unwanted consequences. Therefore, in this study velocity deficits have been predicted and aerodynamic analysis on turbines in the far wake is carried out from these velocity profiles. Ainslie's eddy viscosity wake model is adopted to determine a wake velocity and aerodynamic analysis on wind turbines is predicted by the numerical methods such as blade element momentum theory(BEMT) and vortex lattice method(VLM). The results show that velocity recovery is more rapid in the wake region with higher turbulence intensity. Since the velocity deficit is larger when the turbine has higher thrust coefficient, there is a huge aerodynamic power loss at the downstream turbine.

• 대한기계학회논문집B
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• 제33권7호
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• pp.495-505
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• 2009

A two-dimensional circular cylinder freely falling in a channel has been simulated by using immersed boundary - lattice Boltzmann method (IB-LBM) in order to analyze the characteristics of motion originated by the interaction between the fluid flow and the cylinder. The wide range of the solid/fluid density ratio has been considered to identify the effect of the solid/fluid density ratio on the motion characteristics such as the falling time, the transverse force and the trajectory in the streamwise and transverse directions. In addition, the effect of the gap between the cylinder and the wall on the motion of a two-dimensional freely falling circular cylinder has been revealed by taking into account a various range of the gap size. As the cylinder is close to the wall at the initial dropping position, vortex shedding in the wake occurs early since the shear flow formed in the spacing between the cylinder and the wall drives flow instabilities from the initial stage of freely falling. In order to consider the characteristics of transverse motion of the cylinder in the initial stage of freely falling, quantitative information about the cylinder motion variables such as the transverse force, trajectory and settling time has been investigate.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 전기학술대회논문집
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• pp.1149-1154
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• 2005

The finite difference lattice Boltzmann method(FDLBM) is a quite recent approach for simulating fluid flow, which has been proven as a valid and efficient tool in a variety of complex flow problems. It is considered an attractive alternative to conventional FDM and FVM, because it recovers the Navier-Stokes equations and is computationally more stable, and easily parallelizable to simulate for various laminar flows and a direct simulation of aerodynamics sounds. However, the research of a numerical simulation of turbulent flow by FDLBM, which is important to analyze the structure of turbulent flow in engineering fields, is not carried out. In this research, the FDLBM built in the turbulent model is applied, and a flowfield around 2-dimensional square to validate the applied model with 2D9V is simulated. Besides, 2D computation of the cavity noise generated by flow over a cavity at a Mach number of 0.1 and a Reynolds number based on cavity depth of 5000 is calculated. The computation result is well presented a understanding of the physical phenomenon of tonal noise occurred primarily by well-jet shear layer and vortex shedding and an aeroacoustic feedback loop.

• 한국항공운항학회지
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• 제30권4호
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• pp.57-64
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• 2022

A study on propllers for unmaned aerial vehicles is conducted using the open softwares. Since the shape of the propeller is closely related to the thurst characteristics of the propulsion system, adopting an appropriate propeller will significantly reflect stable aerodynamic performances. In this study, propellers for unmanned aerial vehicles were modeled by using OpenVSP and Propel for comparison, the thrust characteristics according to the number of blades and the diameter of the propeller were analyzed. In addition, the tendency of thrust characteristics according to various propeller pitch angles was confirmed. Based on the analysis results of this study, the applicability of the propeller shape to the design of the unmanned aerial vehicle was confirmed. It is shownthat the analysis results of this study can be utilized when modeling the propeller shape in research such as a conceptual design of unmanned aerial vehicle. In this case, it should be noted that OpenVSP does not involve the viscous effect of air.

• 한국항공우주학회지
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• 제40권8호
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• pp.695-702
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• 2012

본 연구에서는 개념설계 단계에서의 해석 결과의 정확도를 높이기 위한 다정밀도 해석과 모든 분야의 요구도를 만족하기 위한 다분야통합 설계 최적화 기법을 적용하였다. 무인항공기의 해석을 위하여 경험식 기반의 저정밀도 해석도구들이 초기 사이징, 공력, 추진, 임무, 중량, 성능, 안정성 도구들로 모듈화되어 개발 및 검증되었다. 개발된 해석도구를 이용하여 설계통합 프로그램을 구성하고, 설계의 정확도를 증가시키기 위하여 다정밀도 해석에 와류 격자법을 이용하였다. 다분야통합 설계 최적화를 위하여 MDF 기법이 적용되었다. 또한 최적화 도구로는 구배기반 최적화 기법을 적용하였다. 제시한 방법의 타당성을 밝히기 위하여, 저정밀도 해석만을 적용한 방법과 다정밀도 해석을 적용한 두 가지 방법의 최적화 결과를 비교하여 본 연구에서 제안된 다정밀도 해석이 개념설계 단계에서 적용 가능함을 보였다.

• 한국항공우주학회지
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• 제36권2호
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• pp.156-162
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• 2008

본 연구에서는 자유후류기법을 이용하여 복합재 무힌지 로터 블레이드에 대한 정적 공탄성 해석을 수행하였다. 1차원 보의 거동을 해석하기 위하여 대변형 보 이론이 적용되었다. 또한, 복합재 블레이드의 단면 해석을 위하여 이방성 보 이론이 적용되었다. 공탄성 해석에 필요한 공력 하중들은 와류격자법(VLM)에 기초한 3차원 공기력 모델을 통하여 계산되었다. 이때, 정지비행시의 후류는 순차적 시간 적분 자유후류법을 통하여 묘사되었다. 복합재 무힌지 로터 블레이드의 정적 변형에 대한 해석 결과를 2차원 준정상 공기력과 경험후류기법을 통한 해석 결과들과 비교하여 살펴보았다. 결과적으로, 정지비행시 후류 효과에 의해 정적 변형의 결과가 달라짐을 확인하였다.

• 한국항공우주학회지
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• 제44권6호
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• pp.520-529
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• 2016

본 연구의 목적은 중고도-장기체공 무인기의 성능을 역설계를 통해 분석하는 것이며, 역설계를 위한 모델로 RQ-1 Predator를 선정하였다. CATIA 프로그램을 사용하여 RQ-1 Predator의 외형에 대한 형상과 중량 분포를 생성하였다. RQ-1 Predator의 공력특성은 주로 와류격자법과 경험식을 조합하여 수행하였으며, 추진 성능은 Howe의 경험식을 통해 수행되었다. 상승률, 실용상승한도, 항속 거리, 그리고 체공 시간에 대한 역설계를 수행하였으며, 역설계 결과가 참고문헌과 잘 일치함을 확인하였다.

• 대한조선학회논문집
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• 제38권4호
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• pp.11-22
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• 2001

프로펠러-WIG(Wing in Ground Effect)선의 상호작용 및 성능을 포텐셜 유동에 의해 해석하였다. 프로펠러는 보오텍스 격자법(VLM)을 사용하였고 WIG선은 포텐셜 기저 패널법을 사용하여 각 경계조건을 만족시키면서 반복계산을 통하여 상호작용 및 성능을 해석하였다. 자유수면은 강체로 가정하여 경상법을 사용하였다. 프로펠러-WIG의 상호작용 및 성능을 해석하기에 앞서 발표된 실험결과와 계산결과가 있는 MP101 프로펠러와 MR-21 타의 상호작용 및 성능해석을 수행하여 개발된 프로그램의 정도를 검증하였다. 프로펠러-WIG선의 상호작용해석은 프로펠러의 부착위치, 직경 및 회전수의 변화에 따른 비행고도 높이 변화에 대한 양력 및 피치모멘트를 계산하여 비교하였다. 날개 앞에 부착된 프로펠러는 WIG선의 양력을 급격히 향상시키며 정적안정성을 향상시킴을 알았다. 따라서 적절한 프로펠러의 크기, 부착위치 및 회전수의 선택이 PARWIG선의 성능향상을 위해 필수적임을 알았다.

• 대한조선학회논문집
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• 제49권6호
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• pp.528-533
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• 2012

Flexible composite propellers are subject to large deformation under heavy loading, and hence the hydrodynamic performance of deformed propeller might deviate from that of the metallic propeller under negligible deformation. To design the flexible propeller, it is therefore necessary to be able to evaluate the structural response of the blades to the hydrodynamic loadings, and then the influence of the blade deformation upon the hydrodynamic loadings. We use the lifting-surface-theory-based propeller analysis and design codes in solving the hydrodynamic problem, and the finite-element-method program formulated with 20-node iso-parametric solid elements for the analysis of the structural response. The two different hydrodynamic and structural programs are arranged to communicate through the carefully-designed interface scheme which leads to the derivation of the geometric parameters such as the pitch, the rake and the skew distributions common to both programs. The design of flexible propellers, suitable for manufacturing, is shown to perform the required thrust performance when deformed in operation. Sample design shows the fast iteration scheme and the robustness of the design procedure of the flexible propellers.