• 한국전산유체공학회지
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• 제13권3호
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• pp.28-34
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• 2008

In engineering application of large eddy simulation, there are still questions as follows grid dependency on numerical results, the effect of upwind scheme against a calculation instability, appropriate boundary conditions dealing with turbulence fluctuation and the performance of SGS models. In this study, in order to develop the LES to the engineering application, large eddy simulation was carried out to investigate the effect of upwind scheme, turbulent subgrid model and the grid dependancy of the flow around a wall-mounted cube in a channel at Re=40,000 based on cubic height and bulk mean velocity. The computed velocities, turbulence quantities, separation and reattachment length were evaluated compared with the experimental results of R. Matinuzzi and C. Tropea.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2009년도 정기총회 및 추계학술대회 논문집
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• pp.206-208
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• 2009

In this paper, a systematical controller design method for a twostage grid-connected photovoltaic power conditioning system is proposed. For a pre-stage boost converter to achieve the stable operation in the entire region of solar array, the digital resistive current mode controller is used. This algorithm is very simple to implement with a digital controller and there is no power stage parameter dependency in the controller design. For a post-stage single-phase full-bridge inverter, a PI controller with a feedforward compensation for the inner current control is employed. Furthermore, in case that the operating point of the solar array under varying environmental conditions is higher than the required voltage for the inverter current control, the bypass mode for the boost converter is possible for the more efficient operation. The proposed control scheme is validated through the experiment of the prototype two-stage power conditioning system hardware with a 200W solar array.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 추계 학술대회논문집
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• pp.81-85
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• 2005

Three-dimensional steady incompressible laminar entry flows in a square duct of $90^{\circ}$ bend are numerically simulated by a new solution code(PowerCFD) using unstructured cell-centered method. Solutions are obtained with three unstructured grid types of hexahedron, prism and hybrid at a Reynolds number, based on the hydraulic diameter and bulk velocity, of 790. Interesting features of the flow are presented in detail. Detailed comparisons between the computed solutions and the available experimental data are given mainly for the velocity distributions at cross-sections in a $90^{\circ}$ bend of a square duct with fully-developed entry flows. It is found that the code is capable of producing the nature of laminar flow in curved square duct with no grid type dependency.

• 대한조선학회논문집
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• 제44권4호
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• pp.370-378
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• 2007

In this study. a numerical analysis has been performed for the turbulent flow around a 15,000TEU twin-skeg container ship using a commercial CFD code. FLUENT. The computed results have been compared with the model test data from MOERI. We investigated viscous resistance coefficient. wake distribution and characteristics of the shear flow according to the grid numbers. Although the free surface is approximated by the plane of symmetry in this work. the calculated axial velocity and transverse vector show a good agreement with the MOERI experimental data except for the region of 0.9 level of axial velocity at the propeller plane. The numerical analysis show that commercial CFD code is useful tool for the evaluation of complex hull form with twin-skegs.

• 한국유체기계학회 논문집
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• 제19권1호
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• pp.37-44
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• 2016

In this study, a parametric study of a centrifugal pump with double volute has been performed numerically using three-dimensional Reynolds-averaged Navier-Stokes equations. The shear stress transport model was selected as turbulence closure through turbulence model test. The finite volume method and unstructured grid system were used for the numerical analysis. The optimal grid system in the computational domain was determined through a grid dependency test. The expansion coefficient, circumferential and radial starting positions and length of divider were selected as the geometric parameters to be tested. And, the hydraulic efficiency and the radial thrust coefficient were considered as performance parameters. It was found that the radial thrust and hydrualic efficiency are more sensitive to the expansion angle and circumferential starting position of the divider than the other geometrical parameters.

• 한국수소및신에너지학회논문집
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• 제28권1호
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• pp.113-119
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• 2017

An investigation on aerodynamic performance of a highly-loaded axial fan has been conducted to find the effects of tip injection and casing groove on aerodynamic performance in this study. Three-dimensional Reynolds-averaged Navier-Stokes equations with $k-{\varepsilon}$ turbulence model were used to analyze the fluid flow in the fan with Fluid-Structure Interaction (FSI) analysis. The hexahedral grid was used to construct computational domain, and the grid dependency test drew the optimal grid system. FSI analysis was also carried out to predict the deformation of rotor and stator blades, and the effect of deformation on the aerodynamic performance of axial fan was analyzed compared to the performance predicted without FSI analysis.

• 한국수소및신에너지학회논문집
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• 제31권3호
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• pp.314-321
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• 2020

In this work, a preliminary design of an inlet guide vane and runner for developing a 2.5 kW hydraulic turbine was conducted by using computational fluid dynamic analysis. Three-dimensional Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model were used to analyze the fluid flow in the hydraulic turbine. The hexahedral grid system was used to construct computational domain, and the grid dependency test was performed to obtain the optimal grid system. Velocity triangle diagram considering the flow angles of the inlet guide vane and runner was analyzed to obtain a basic geometry of the inlet guide vane and runner. Through modification of the preliminary design, the hydraulic performances of the turbine have improved under overall drop conditions. Especially, the efficiency and power of the turbine increased by 0.95% and 1.45%, respectively, compared to those of the reference model.

• 한국항공우주학회지
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• 제45권12호
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• pp.1021-1030
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• 2017

본 논문은 유한요소 열해석 시 불일치하는 격자 접촉면의 열교환계수를 효과적으로 계산하는 방법에 대해 논의한다. 원래 유한요소해석은 두 경계면 사이의 격자가 일치해야 하는데, 복잡하고 다양한 재질의 형상들의 접촉면을 모두 일치하기 위해서는 많은 수고와 계산량이 소요된다. 본문은 이를 극복하기 위해 서로 다른 두 격자면의 접촉 열교환계수를 각 절점으로 효과적으로 분배하는 새로운 기법을 제안하였다. 제시된 기법의 지향점을 서술하고 이를 위해 격자면의 형상에 의존성이 낮은 절점 가중치 분배 기법을 서술하였다. 그리고 이를 3차원의 곡면 접촉면에도 적용하여 제시한 방법론의 범용성을 확인함으로서 열해석을 포함한 여타 유한요소 해석 기법에도 적용 가능함을 알 수 있다.

• 한국수소및신에너지학회논문집
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• 제31권1호
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• pp.151-159
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• 2020

This study aimed to investigate the performance characteristics of vertical axis turbine of tidal energy convertor. Three-dimensional Reynolds-averaged Navier-Stokes equation with shear stress transport turbulence model has been solved to analyze the fluid flow of the vertical axis turbine. The hexahedral grids have been used to construct the computational domain and the grid dependency test has been performed to find the optimum grid system. Four steps have been carried out to design the vertical axis turbine of the 100 kW class tidal energy convertor.

• 한국유체기계학회 논문집
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• 제19권5호
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• pp.42-49
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• 2016

Aerodynamic analysis of a low-voltage electric motor has been performed with various inlet vent shapes. Effects of inlet vent shape on aerodynamic performance of a motor cooling fan have been investigated numerically using three-dimensional Reynolds-averaged Navier-Stokes equations. The k-${\varepsilon}$ turbulence model was used for the analysis of turbulence. The finite volume method and unstructured tetrahedral grids were used in the numerical analysis. Optimal grid system in the computational domain was selected through a grid-dependency test. From the results of the flow analysis, considerable energy loss by flow separation was observed in the flow passage. It was found that mass flow rate through the cooling fan in the low-voltage motor can be increased by modifying the inlet vent shape. And, some inlet vent shapes were suggested to improve the aerodynamic performance of the motor cooling fan.