• Journal of the Society of Naval Architects of Korea
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• v.31 no.4
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• pp.58-65
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• 1994

It is very important to understand characteristics of solution due to the variation of computational grid sizes, especially when turbulence model not incorporating wall-function is used. The present paper performs numerical investigation on the grid dependency of numerical solution for three dimensional turbulent flow field around a ship. In the present study a finite volume method with a modified sub-grid scale turbulence model and a numerically constructed non-orthogonal curvilinear coordinate system capable of conforming complex ship geometries are used. Numerical studies are then performed for a mathematical Wigley hull and the Series 60, $C_B=0.8$ hull forms. The results for various grid sizes are compared with each other and with measured data to show grid dependencies of numerical solutions.

• Transactions of the Korean hydrogen and new energy society
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• v.31 no.4
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• pp.387-394
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• 2020

A parametric study of a 2.5 kW class propeller type micro hydraulic turbine was performed. In order to analyze the internal flow characteristics in the hydraulic turbine, three dimensional Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model were used and the hexahedral grid system was used to construct computational domain. To secure the reliability of the numerical analysis, the grid dependency test was performed using the grid convergence index method based on the Richardson extrapolation, and the grid dependency was removed when about 1.7 million nodes were used. For the parametric study, the axial distance at shroud span (L) between the inlet guide vane and the runner, and the inlet and outlet blade angles (β₁, β₂) of the runner were selected as the geometric parameters. The inlet and outlet angles of the runner were defined in the 3 spans from the hub to tip, and a total of 7 geometric parameters were investigated. It was confirmed that the outlet angles of the runner had the most sensitive effect on the power and efficiency of the micro hydraulic turbine.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.6
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• pp.445-451
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• 2018

This paper describes on introduction of CASE 4(Delta Wing) for EFD-CFD comparison workshop which is in charged of aerodynamic subcommittee of The Korean Society for Aeronautical and Space Science. The wind tunnel test will be performed later, angle of attack is set -5~20deg and mach number is set 0.7, 0.85, 1.2 to solve the transonic flow. The simulation test of grid dependency is conducted to determine the proper grid size of delta wing analysis. The tendency of lift and drag coefficient is determined according to the change of angle of attack based on the selected grid size.

• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.19-22
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• 1998

Automatic mesh generation procedures applied to industrial now problems lead to complex mesh topologies where usually no special considerations to mesh resolution are taken. In the present study a fast and flexible solution algorithm in combination with generalized higher order discretization schemes is presented and its application to intake port calculation is demonstrated.

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.5
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• pp.550-559
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• 2014

Hydraulic performance of the 1 inch ball valve have been analyzed based on the three-dimensional Reynolds-averaged Navier-Stokes analysis and an experiment. The experimental test rig of the 1 inch ball valve has been developed to investigate pressure drop for the 1 inch ball valve. The numerical model, which has reliability and effectiveness, has been constructed through the grid dependency test and validation with the results of the experiment. Shear stress transport turbulence model has been used to enhance an accuracy of the turbulence prediction in the pipeline and ball valve, respectively. Effects of the ball valve angle on the flow characteristics and friction performance have been evaluated.

• Transactions of the Korean Society of Automotive Engineers
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• v.23 no.2
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• pp.191-198
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• 2015

In this study, the flow characteristics at the ventilation holes was analyzed by using numerical method when carbon composite brake disk was rotated at a constant speed. In order to ensure the validity of the analysis results, grid dependency test was performed by considering the accuracy and appropriateness, and 4mm mesh size was selected for decrease of the maximum error rate 63.6%. As a result, the outside air flows in the clearance between the disk and shaft in case of B model. whereas, the outside air flows in the clearance or the outlet of the ventilation holes in case of A and C models. And also average static pressure at the outlet was changed depending on shape of the ventilation holes and rotational speed of the disk in case of A and C models. Besides, in the B model, intake air according to the clearance goes with side surface of ventilation hole, and so increased by mean velocity of 4.64m/s and mean pressure of 0.58pa in the ventilation hole outlet, in case of disk rotational speed of 146.21rad/s.

• Journal of computational fluids engineering
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• v.10 no.4 s.31
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• pp.18-23
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• 2005

Numerical simulations of two-dimensional steady incompressible lid-driven flow in a square cavity are presented by a new solution code(PowerCFD) which adopts an unstructured cell-centered method. Solutions are obtained for configurations with a Reynolds number as high as 10,000 with both rectangular and hybrid types of unstructured grid mesh in order to validate the code's independency of grid type. Interesting features of the flow are presented in detail and comparisons are made with benchmark solutions found in the literature. It is found that the code is capable of producing accurately the nature of the lid-driven cavity flow at high Reynolds numbers with no grid type dependency.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.2
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• pp.90-97
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• 2004

Flow mechanism of contractive and dilative motion is numerically investigated to obtain a propulsive force in highly viscous fluid. An axisymmetric code is developed with unstructured grid system based on cell-centered scheme. It is validated by comparing with the results of Stokes approximation for the problem of uniform flow past a sphere in low Reynolds number(R$_{n}$=1). The validated code is applied to the simulation of contractive and dilative periodic motion of body whose results are quantitatively compared with the two dimensional case. In order to investigate the grid dependency, two different grids are applied to the present computations. The present study provides key information for the development of an axisymmetric Micro-hydro-robot.t.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.210-217
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• 2011

Recently, research on evaluating thermal comfort by using CFD has been vigorously active. This research evaluates not only distribution of temperature and air flow analysing but also thermal comfort in indoor space by applying human model. But research of human model's shape, Grid characteristic and turbulence model has not yet been studied. In this paper, human model's shape, physical characteristic of variable Grid, and change of turbulence model has been studies by CFD. In this study. FLUENT is used for analysis and PMV(predicted Mean Vote), PPD(Predicted Percentage Dissatisfied) and EHT(Equivalent Homogeneous Temperature} are used for evaluation and comparison of thermal comfort. As a result, it shows that shape of CSP and lattice features does not affect on global flow field or evaluation on PMV, PPD. However, it demonstrates more precise result from evaluation of thermal comfort by equivalent temperature when it used detailed human model considering prism grid.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.03a
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• pp.50-58
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• 2003

We have developed a locally variable time-step scheme matching with discontinuous grids in the flute-difference method for the efficient simulation of seismic wave propagation. The first-order velocity-stress formulations are used to obtain the spatial derivatives using finite-difference operators on a staggered grid. A three-times coarser grid in the high-velocity region compared with the grid in the low-velocity region is used to avoid spatial oversampling. Temporal steps corresponding to the spatial sampling ratio between both regions are determined based on proper stability criteria. The wavefield in the margin of the region with smaller time-step are linearly interpolated in time using the values calculated in the region with larger one. The accuracy of the proposed scheme is tested through comparisons with analytic solutions and conventional finite-difference scheme with constant grid spacing and time step. The use of the locally variable time-step scheme with discontinuous grids results in remarkable saving of the computation time and memory requirement with dependency of the efficiency on the simulation model. This implies that ground motion for a realistic velocity structures including near-surface sediments can be modeled to high frequency (several Hz) without requiring severe computer memory