• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.10
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• pp.975-983
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• 2009

This paper presents the work being carried out in order to deduce hover performance of a small-scale single rotor blade as a preliminary study of a small coaxial rotor helicopter development. As an initial research, a test stand capable of measuring thrust and torque of a small-scale rotor blade in hover state was constructed and fabricated. The test stand consists of three parts; a rotating device, a load measuring sensor and a data acquisition system. Thrust and torque were measured with varying collective pitch angle at fixed RPM. Through this research, hover performance tests were conducted for a small-scale single rotor blade operating in low Reynolds number ($Re\;{\approx}3{\times}10^5$), as well as for verifying the test stand itself for acquiring hover performance.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.31-38
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• 2005

Aerodynamic influence coefficient linearly relates pressure with downwash in panel method for load analysis in which the viscosity of a flow is ignored and the compressibility cannot be taken into account in transonic region. Since the planform of an aerodynamic surface determines the coefficient, the panel method has a limit to the analysis of low Reynolds number flow. The accuracy of the pressure distribution can be improved by a direct correction to the pressure or a correction to the downwash, which is considered the change of camber or thickness, using the aerodynamic coefficients from wind tunnel test as constraints. A premultiplying correction method as well as a postmultiplying correction method is applied to a micro air vehicle to provide more accurate aerodynamic pressure for trim and load analyses. Theoretical aerodynamic pressure is obtained from the panel method. Correction factor matrix and correct pressure coefficient are computed for the conditions with two constraints in addition to single constraint. The postmultiplying correction method gives a better improvement in pressure distribution on micro air vehicle due to the flow characteristics on it.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.590-593
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• 2009

To identify the detailed 3D flow characteristics of a model scramjet engine, a unified 3D numerical analysis was performed. The numerical domain of concern includes the entire flow path of the model scramjet engine extending from the intake to the nozzle exhaust. Turbulent models($k-{\omega}$ SST and low Reynolds number k-e with Sarkar model) were applied with comparison of experiment result. Intake side wall's effect on flow characteristics was analyzed in view points of flow quality at inlet duct and near the flame holder as well. The code is paralleled with multi-block feature using MPI(Massage Passing Interface) library to speed up the 3D calculation.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.1
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• pp.61-69
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• 2013

Numerical simulations have been performed for assessment of compressibility correction of two-equation turbulent models suitable for large scale separation flows perturbed by a pintle strokes. Two-equation turbulence models, the low Reynolds k-${\varepsilon}$ and the k-${\omega}$ SST models with or without compressibility correction proposed by Wilcox and Sarkar are evaluated. The detail flow structures are observed and static pressures along nozzle wall are compared with experimental results. Mach disk location and pressure recovery profiles in flow separation region are noticeably distinct between turbulent models of k-${\varepsilon}$ and k-${\omega}$ SST. The compressible effect corrections to those models improve resolving of separation flow behaviors. The compressibility corrections to k-${\varepsilon}$ model have provided very comparable results with test data.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.9
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• pp.759-768
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• 2016

Design and performance analysis of propeller for solar-powered HALE UAV, EAV-3 are conducted. Experiment points of design variables are obtained by using Design of Experiment(DOE) and Kriging meta-model is generated for objective and constraints function. The geometry of propeller is designed by evaluating the response surface with requirement and restrictions. The validity of the design is verified by meta-model based optimization. Computational analyses are carried out by using commercial CFD code and the results are compared with those from a design code and wind tunnel test. The results showed good agreement with predictions of the design code at the design altitude. Also, it is confirmed that the blockage effect due to the measurement device and support strut is included in the test data and the results including this effect compare well with the test data.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.5
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• pp.337-344
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• 2024

This study presents a deep learning-based framework to predict the aerodynamic performance of low Reynolds number airfoils. The framework employs a convolutional neural network (CNN) combined with a variational autoencoder (VAE) to efficiently handle large datasets. Moreover, the signed distance function is used as the network input to represent the airfoil configuration in the image data and parameterize the CNN. A novel generative model based on projection-based manifold learning is proposed to overcome the data mining limitation of computational fluid dynamics which may incur significant computational costs. The interpolation and extrapolation accuracy of the proposed framework is evaluated using the NACA 4-digit airfoil configuration.The results show improved accuracy via data augmentation performed by the proposed generative model.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.23 no.3
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• pp.117-126
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• 1987

The author has analysed profile of flow in rear of motion with single ball with low Reynolds number performed interface layers. For each system whose viscosity of the lower phase is as large as or large that of the upper phase, the profile has based on the thickness of the ball in the lower phase is nearly independent of both the ball single and the physical properties of the upper phase of the solution. The examine of the characteristics between Darwin's total displacement of the fluid and data obtained in this study, the averaged volume of each cases was corrected by the viscosity in the lower phase. When the viscosity in the lower phase is less than that of the upper phase, the volume based on the displacement of the fluid in rear region of ball are influenced by both ball size and the viscosity ratio of the upper phase to the lower phase. In the range of the Reynolds number less than a constant values, the volume ratio is influenced by both Reynolds number and Moltion number but mainly Reynolds. In range of Reynolds number over than the value, the volume ratio is independent of Reynolds number, but influenced by Moltion number.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.6
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• pp.2267-2275
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• 2013

Existing conventional model for analysis of shallow water flow just assumed the internal boundary condition as free-slip, which resulted in the wrong prediction about the velocity, vorticity, water level, shear stress distribution, and time variation of drag and lift force around a structure. In this study, a finite element model that can predict flow characteristics around the structure accurately was developed and internal boundary conditions were generalized as partial slip condition using slip length concept. Laminar flow characteristics behind circular cylinder were analyzed by varying the internal boundary conditions. The simulation results of (1) time variations of longitudinal and transverse velocities, and vorticity; (2) wake length; (3) vortex shedding phenomena by slip length; (4) and mass conservation showed that the vortex shedding had never observed and laminar flow like creeping motion was occurred under free-slip condition. Assignment of partial slip condition changed the velocity distribution on the cylinder surface and influenced the magnitude of the shear stress and the occurrence of vorticity so that the period of vortex shedding was reduced compared with the case of no slip condition. The maximum mass conservation error occurred in the case of no slip condition, which had the value of 0.73%, and there was 0.21 % reduction in the maximum mass conservation error by changing the internal boundary condition from no slip to partial slip condition.