• International Journal of Railway
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• v.4 no.4
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• pp.109-115
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• 2011

An analysis and design method for reducing aerodynamic noise in high-speed trains based on biomimetics of noiseless flight of owl is proposed. Five factors related to the morphology of the flight feather have been selected, and the candidate optimal shape of the flight feather is determined. The turbulent flow field analysis demonstrates that the optimal shape leads to diminished vortex formation by causing separation of the flow as well as allowing the fluid to climb up along the surface of the flight feather. To determine the effect of scaling of the owl's flight feather on the noise reduction, a two-fold and a four-fold scaled up model of the feather are constructed, and the numerical simulations are carried out to obtain the aerodynamic noise levels for each scale. Original model is found to reduce the noise level by 10 dBA, while two-fold increase in length dimensions reduces the noise by 12 dBA. Validation of numerical solution using wind tunnel experimental measurements is presented as well.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.3
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• pp.26-31
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• 2005

An efficient estimation of the aerodynamic characteristics for missile configurations is essential in the preliminary stage of a missile design. In this study, a Missile DATCOM family code based on the semi-empirical method was utilized for this purpose. In order to check the accuracy and reliability of the code several test cases have been considered: subsonic flow with high angles of attack and supersonic flow with moderate angles of attack. It turned out that the code in general provides prediction in qualitative agreement with the experimental data and results by other works. Finally, the code was applied to a more complicated missile configuration with canard and freely spinning tail fin.

• Journal of Aerospace System Engineering
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• v.17 no.6
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• pp.94-99
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• 2023

Recently, renewable energy has been widely used as a source of wind energy and solar energy due to the shortage of fossil fuels and environmental problems. Against this backdrop, wind energy is emerging as an important energy source, and the wind power market is showing rapid growth worldwide. In this study, a high-efficiency wind turbine blade was designed with an integrated blade aerodynamic design for prior research on separate blades. The blade airfoil was applied as NACA 4418, and it was verified by comparing it with the analysis results to evaluate the newly designed blade.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.57-65
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• 2009

An efficient and high-fidelity design approach for wing-body shape optimization is presented. Depending on the size of design space and the number of design of variable, aerodynamic shape optimization process is carried out via different optimization strategies at each design stage. In the first stage, global optimization techniques are applied to planform design with a few geometric design variables. In the second stage, local optimization techniques are used for wing surface design with a lot of design variables to maintain a sufficient design space with a high DOF (Degree of Freedom) geometric change. For global optimization, Kriging method in conjunction with Genetic Algorithm (GA) is used. Asearching algorithm of EI (Expected Improvement) points is introduced to enhance the quality of global optimization for the wing-planform design. For local optimization, a discrete adjoint method is adopted. By the successive combination of global and local optimization techniques, drag minimization is performed for a multi-body aircraft configuration while maintaining the baseline lift and the wing weight at the same time. Through the design process, performances of the test models are remarkably improved in comparison with the single stage design approach. The performance of the proposed design framework including wing planform design variables can be efficiently evaluated by the drag decomposition method, which can examine the improvement of various drag components, such as induced drag, wave drag, viscous drag and profile drag.

• The KSFM Journal of Fluid Machinery
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• v.5 no.3 s.16
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• pp.40-45
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• 2002

Since the previous cut-and-try design algorithm requires much cost and time, the automated design technique with the CFD and optimum design algorithm has recently been concerned. In this work, the Navier-Stokes equation was solved to gain more detailed viscous flow information of cascade with rotor-stator interactions. The H-grid embedded by O-grid was generated to obtain more accurate solution by eliminating the branch cut of H-grid near airfoil surface. To handle the relative motion of the rotor to the stationary stator, the sliding multiblock method was applied and the cubic-spline interpolation was used on the block interface boundary. To validate present procedure, the time-averaged aerodynamic loads were compared with experimeatal data. A good agreement was obtained. The Modified Method of Feasible Direction (MMFD) was used to carry out the sensitivity analysis of the change of aerodynamic performance by the changes of the cascade geometry. The present optimization of the cascade gave a dramatic reduction of the drag while the lift maintains at the value within the user-specified tolerance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.11 s.254
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• pp.1084-1092
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• 2006

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.

• Journal of the Korean Society of Visualization
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• v.10 no.1
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• pp.27-33
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• 2012

This paper describes a new design of small-scale horizontal wind blade, called spiral wind turbine blade. Theoretical and numerical approaches on the prediction of aerodynamic performance of the blade have been conducted. A theoretical equation is successfully derived using the angular momentum equation to predict aerodynamic characteristics according to the design shape parameters of spiral blade. To be compared with the theoretical value, a numerical simulation using ANSYS CFX v12.1 is performed on the same design with the theoretical one. Large scale tip vortex is captured and graphically presented in this paper. The TSR-$C_p$ diagram shows a typical parabolic relation in which the maximum efficiency of the blade approximately 25% exists at TSR=2.5. The numerical simulation agrees well with that of the theoretical result except at the low rotational speed region of 0~20 rad/s.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.38-42
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• 2004

The optimal design for a leading car considering the aerodynamic resistance is required on the high-speed train due to increasing of ratio of drag force with proportion for the square of velocity. The aerodynamic analysis using CFD in the stage of concept design offers more economical analysis method which is used to estimate the influence of flow and pressure around the leading car than the experimental method using the Mock-up. In this study, we want to assist the artistic design with aerodynamics analysis in order to get the optimal design for leading car made of composite material. The results of aerodynamic analysis for two leading car models, which one is expressed with lineal beauty and the other is with curvaceous beauty, are compared with each other and offer the proposal of modification for two models in order to decrease be drag force. The shape of curvaceous model is better for the pressure force but slightly worse for the viscous force than the other. The Fluent software is used for the calculation of flow profile in this study.

• Proceedings of the KSR Conference
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• 2003.10c
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• pp.351-357
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• 2003

The optimal design for a leading car considering the aerodynamic resistance is required on the high-speed train due to increasing of ratio of drag force with proportion for the square of velocity. The aerodynamic analysis using CFD in the stage of concept design offers more economical analysis method which is used to estimate the influence of flow and pressure around the leading car than the experimental method using the Mock-up. In this study, we want to assist the artistic design with aerodynamics analysis in order to get the optimal design for leading car with the operation speed at 180km/h. The results of aerodynamic analysis for two leading car models which one is expressed with lineal beauty and the other is with curvaceous beauty are compared with each other and they offer the proposal of modification for two models in order to decrease the drag force. The shape of curvaceous model is better for the pressure force but slightly worse for the viscous force than the other. The Fluent software is used for the calculation of flow profile in this study.

• Advances in aircraft and spacecraft science
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• v.6 no.1
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• pp.31-49
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• 2019

Flutter is a dangerous phenomenon encountered in flexible structures subjected to aerodynamic forces. This includes aircraft, helicopter blades, engine rotors, buildings and bridges. Flutter occurs as a result of interactions between aerodynamic, stiffness and inertia forces on a structure. The conventional method for designing a rotor blade to be free from flutter instability throughout the helicopter's flight regime is to design the blade so that the aerodynamic center (AC), elastic axis (EA) and center of gravity (CG) are coincident and located at the quarter-chord. While this assures freedom from flutter, it adds constraints on rotor blade design which are not usually followed in fixed wing design. Periodic Structures have been in the focus of research for their useful characteristics and ability to attenuate vibration in frequency bands called "stop-bands". A periodic structure consists of cells which differ in material or geometry. As vibration waves travel along the structure and face the cell boundaries, some waves pass and some are reflected back, which may cause destructive interference with the succeeding waves. In this work, we analyze the flutter characteristics of a helicopter blades with a periodic change in their sandwich material using a finite element structural model. Results shows great improvements in the flutter forward speed of the rotating blade obtained by using periodic design and increasing the number of periodic cells.