Juhee Lee

Aerodynamic Characteristics and Shape Optimization of Airfoils in WIG Craft Considered Ground Effect

Shape optimization of airfoil in WIG craft has been performed by considering the ground effect. The WIG craft should satisfy various aerodynamic characteristics such as lift, lift to drag ratio, and static height stability. However, they show a strong trade-off phenomenon so that it is difficult to satisfy aerodynamic properties simultaneously. Optimization is carried out through the multi-objective genetic algorithm. A multi-objective optimization means that each objective is considered separately instead of weighting. Due to the trade-off, pareto sets and non-dominated solutions can be obtained instead of the unique solution. NACA0015 airfoil is considered as a baseline model, shapes of airfoil are parameterized and rebuilt with four-Bezier curves. There are eighteen design variables and three objective functions. The range of design variables and their resolutions are two primary keys for the successful optimization. By two preliminary optimizations, the variation can be reduced effectively. After thirty evolutions, the non-dominated pareto individuals of twenty seven are obtained. Pareto sets are all the set of possible and excellent solution across the design space. At any selections of the pareto set, these are no better solutions in all design space.

Global Shape Optimization of Airfoil Using Multi-objective Genetic Algorithm

The shape optimization of an airfoil has been performed for an incompressible viscous flow. In this study, Pareto frontier sets, which are global and non-dominated solutions, can be obtained without various weighting factors by using the multi-objective genetic algorithm An NACA0012 airfoil is considered as a baseline model, and the profile of the airfoil is parameterized and rebuilt with four Bezier curves. Two curves, front leading to maximum thickness, are composed of five control points and the rest, from maximum thickness to tailing edge, are composed of four control points. There are eighteen design variables and two objective functions such as the lift and drag coefficients. A generation is made up of forty-five individuals. After fifteenth evolutions, the Pareto individuals of twenty can be achieved. One Pareto, which is the best of the . reduction of the drag furce, improves its drag to and lift-drag ratio to . Another Pareto, however, which is focused on increasing the lift force, can improve its lift force to , while sustaining its drag force, compared to those of the baseline model.

Optimization of Wings in Ground Effect Using Multi- Objective Genetic Algorithm

The shape optimization using the multi-objective genetic algorithm and the analysis of the 3-dimensional wings in ground effect has been performed. Unlike an airplane flying out of ground effect, wings in ground effect have to satisfy static height stability to cruise steadily above the ground or water surface. In this study, both aerodynamic performance and static height stability are considered as objectives. Due to the multi-objective optimization, the optimal solutions are not unique but a set of non-dominated potential solutions: Pareto optima. After twenty evolutions, 74 non-dominated Pareto optima can be obtained. Three objectives, lift coefficient, lift-to-drag ratio and static height stability, are strongly tradeoff each other so that the unique and dominate solution is not existed. The Pareto optima obtained in this study are placed on the edge of the objective space. From the analysis of the Pareto optima, static height stability was improved at the lower height and the higher angle of attack. The lift-to-drag ratio increases with the lower height since the pressure on the lower wing surface increases while that on the upper surface remains constant. The influence of the tip vortex reduces as ground approached.

Aerodynamic Characteristics of Giromill with High Solidity

풍력발전기는 무한히 재생가능한 바람 에너지를 전기적 에너지로 변환하는 청정 에너지 변환장치Key Words : Symmetric Airfoil(대칭익형), Vertical Axis Wind Turbine(수직축풍력발전기), Giromill(자이로밀), Aerodynamic Characteristics(공기역학적 특성), CFD(전산유체역학), High Solidity(높은 솔리디티), 초록: 3차원 비정상유동해석을 통하여 자이로밀의 공기역학적 특성을 고찰하였다. 일반적으로 소형자이로밀은 구조가 간단하고 솔리디티가 높아 제작이 쉽고 자구동(self-starting)이 가능하다는 장점을 가지고 있다. 그러나 TSR (tip speed ratio)가 4~7인 다리우스풍력발전기와 다르게 1~3정도로 매우 낮다. 본 연구에 사용한 자이로밀은 일정한 단면을 가진 3 개의 직선날개로 구성되어 있으며 솔리디티는 0.75 이다. 솔리디티가 매우 낮은 다리우스풍력발전기와 다르게 자이로밀은 TSR 이 증가함에 따라 날개 상호간의 간섭과 하류에 위치하는 날개로 유입되는 유동속도의 급격한 감소로 인하여 양력이 감소하고 날개의 회전속도에 의하여 주변의 공기가 가속되면서 항력의 증가로 성능이 저하되었다. 이로 인하여 TSR 이 2.4에서 최고의 성능을 나타내며 이후로 급격히 감소하는 것을 알 수 있었다. Abstract: A 3-dimensional unsteady numerical analysis has been performed to evaluate the aerodynamic characteristics of a Giromill. Generally, the structure of a Giromill is simple and therefore easy to develop. In addition, the high solidity of the Gironmill helps improve the self-starting capacity at a low tip speed ratio (TSR). However, contrary to the Darrieus wind turbine which has a TSR of 4–7, a Giromill has a low TSR of 1–3. In this study, the aerodynamic characteristics of the Giromill are investigated using computational fluid dynamics (CFD). Three straight-bladed wings are used, and the solidity of the Giromill is 0.75. In contrast to a Darrieus wind turbine having low solidity, the Giromill shows a sudden decrease in the aerodynamic performance because of the interference between the wings and an increase in the drag on the wings in the downstream direction where wind flow is significantly reduced. Consequently, the aerodynamic performance decreased at a TSR value lower than 2.4.

Aerodynamic Characteristics and Static Height Stability of WIG Effect Vehicle with Direct Underside Pressurization

A 3-dimensional numerical investigation of a WIG effect vehicle with DUP (direct underside pressurization) is performed to predict aerodynamic characteristics and the static height stability. DUP can considerably reduce take-off speed and minimize the hump drag while the vehicle accelerates on the water to take off. The DUP of the model vehicle, Aircat, consists of a propeller in the middle of the fuselage and an air chamber under the fuselage. The air accelerated by the propeller comes into the camber through the channel in the middle of fuselage and augments lift by changing its dynamic pressure to static pressure dramatically. However, the air accelerated by a propeller produces excessive drag and reduces static height stability.

Flow/Heat Transfer Analysis and Shape Optimization of a Heat Exchanger with Internally Finned Tube

Analyses of flow and heat transfer characteristics and shape optimization of internally finned circular tubes have been performed for three-dimensional periodically fully developed turbulent flow and heat transfer. CFD and mathematical optimization are coupled in order to optimize the shape of heat exchanger. The design variables such as fin widths and fin height (h) are numerically optimized by minimizing the pressure loss and maximizing the heat transfer rate for limiting conditions of

Influence of endplate on aerodynamic characteristics of low-aspect-ratio wing in ground effect

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