• 한국전산유체공학회:학술대회논문집
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• 2003.08a
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• pp.219-224
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• 2003

An analysis procedure for the MCFC channel flow has been developed to predict the fuel cell performance. As for the electrochemical reaction, among several chemical reaction models, one that fits the data best is adopted after a comprehensive comparative study. The Wavier-Stokes, energy, and species equations are solved to obtain the velocity, temperature and concentration fields for a specified average current density. The procedure is iterative as the local current density, or the reaction rate, is allowed to vary with the gas composition. A series of calculations are then carried out to examine the effects of gas flow rate, gas composition, gas usage rate, inlet gas temperature, and average current density on the fuel cell performance. The fuel cell characteristics, such as the temperature, current density distributions, and the concentration fields, for various operating conditions are presented and discussed.

• 한국전산유체공학회:학술대회논문집
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• 2003.08a
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• pp.37-42
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• 2003

A vorticity-velocity integro-differential formulation of incompressible Wavier-Stokes equations is described, focusing on a scheme for calculating pressure fields in application of the Lagrangian vortex method in connection with panel methods. It deals with the dynamic coupling among velocity, vorticity and pressure, and the Helmholtz decomposition of the velocity field, through a comparative study with the Eulerian finite volume method, we provide an extensive understanding of the Lagrangian vortex methods for numerical simulations of viscous flows around arbitrary bodies.

• Journal of Hydrospace Technology
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• v.2 no.2
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• pp.1-13
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• 1996

This paper presents the result of a computational study on the wake characteristics of two tanker models, i.e. HSVA and Mystery hull forms. The focus of the study is on the distributions of axial, radial and tangential velocities of the two hull forms in way of the propeller, especially over the propeller disk. The effect of bilge vortices on the velocity distribution is also concerned. For the computation of stern and wake flows of the two hull farms, the incompressible Reynolds-Averaged Wavier-Stokes(RANS) equations are numerically solved by the second order finite difference method, which employs a four stage Runge-Kutta scheme with a residual averaging technique and the Baldwin-Lomax model. The calculated pressure distributions on the hull surface and the axial, radial and tangential velocity distributions over the propeller disk are presented for the two hull forms. Finally, the result of wake analysis for the computed wake distribution over the propeller disk is given in comparison with those for the experimental wake distribution fur the both hull forms.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.404-411
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• 2003

Three-dimensional vortical flow and separated flow topology near the casing wall in an axial flow fan having two different tip clearances have been investigated by a Reynolds-averaged Wavier-Stokes (RANS) flow simulation. The simulation shows that the tip leakage vortex formed close to the leading edge of the blade tip on suction side grows in the streamwise direction. On the casing wall, a separation line is formed upstream of the leakage vortex center due to the interference between the leakage vortex and main flow. The reverse flow is observed between the separation line and the attachment line generated downstream of the trailing edge, and increased with enlarging tip clearance. The patterns of a leakage velocity vector including a leakage flow rate are also analyzed according to two tip clearances. It is noted that the understanding of the distribution of a limiting streamline on the casing wall is very important to grasp the characteristics of the vortical flow in the axial flow fan.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.496-501
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• 2003

Reynolds averaged Wavier-Stokes simulations based on the Reynolds stress model was performed to investigated the effect of inlet flow angle on the distributions of the Reynolds stress tensor inside tip leakage vortex of a linear compressor cascade. Two different inlet flow angles ${\beta}=29.3^{\circ}$(design condition) and $36.5^{\circ}$(off-design condition) were considered. Stress tensor analysis, which transforms the Reynolds stress into the principal direction, was applied to show an anisotropy of the normal stresses. Whereas the anisotropy was highest in the region where the tip leakage vortex collides the suction side of the blade and tip leakage flow enters between blade tip of the pressure side and the endwall, it had the lowest value at the center of tip leakage vortex. It was also found that the magnitude of maximum shear stress at design condition was greater than that of off-design condition.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.520-525
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• 2003

A numerical investigation was performed to determine the effect of airfoil on the optimum flap height using NACA0015 Wells turbine. The five double flaps which have 0.5% chord height difference were selected. A Wavier-Stokes code, CFX-TASCflow, was used to calculate the flow field of the Wells turbine. The basic feature of the Wells turbine is that even though the cyclic airflow produces oscillating axial forces on the airfoil blades, the tangential force on the rotor is always in the same direction. Geometry used to define the 3-D numerical grid is based upon that of an experimental test rig. This paper tries to analyze the optimum double flap of Wells turbine with the numerical analysis.

• Journal of the Korean Society of Safety
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• v.10 no.2
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• pp.56-63
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• 1995

A simulation of contaminant dispersion in a water reservoir has been done using 2-D finite difference method(FDM). The steady state velocity field of the reservoir was computed using stream function-vorticity formulation of Wavier-Stokes equation and continuity equation. Based on the computed steady state velocity field, the transient convective diffusion equation of the contaminant dispersion was computed. For the 1m$\times$1m reservoir model with inlet and outlet attached, it was shown that the center of circulation located toward right. For the numerical values of v =0.01($\textrm{cm}^2$/s) and D=0.6($\textrm{cm}^2$/s) and the flow of 50($\textrm{cm}^3$/s ), it was determined that the outflow had to be shut down in 18 seconds to prevent from severe pollution. Also the required time was computed to be 6 seconds for the inflow of 100 ($\textrm{cm}^3$/s). The result of this study is considered, hopefully, to be useful for the design of the water reservoir systems that are the subjects to various contamination.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.53-56
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• 2004

The mixing characteristics of a multiple transverse injection system in a scramjet combustor were studied with numerical methods. The distance among injectors on mixing characteristics were investigated. The three-dimensional Wavier-Stokes equations including k-w SST turbulence model were solved. It was shown that the mixing characteristics of a multiple transverse injection system were very different from those of a single and a dual injection system; the rear injection flow was strongly influenced by blocking effect due to the momentum flux of the front injection flow and thus had higher expansion and penetration than the front injection flow. The multiple injection system had higher mixing rate, higher penetration but had more losses of stagnation pressure than the single injection system.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.363-366
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• 2006

The effectiveness of two passive control techniques for alleviating the pressure oscillation generated in a supersonic cavity flow is investigated numerically. The passive devices suggested in the present research include a triangular bump and a sub-cavity installed near the upstream edge of a rectangular cavity. The supersonic cavity flow characteristics are examined by using the three-dimensional, unsteady Wavier-Stokes computation based on a finite volume scheme. Large eddy simulation (LES) is carried out to properly predict the turbulent features of cavity flow. The results show that the pressure oscillation near the downstream edge dominates overall time-dependent cavity pressure variations. Such an oscillation is attenuated more considerably using the sub-cavity compared with other methods, and a larger sub-cavity leads to better control performance.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.3
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• pp.145-151
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• 2003

Using computational fluid dynamics (CFD) method, we investigated three-dimensional fluid flow field and particle movement with respect to the injected gas flow rate variation in typical cyclone separator system. The results of numerical investigation were deduced by coupling the analysis of fluid flow field with Wavier-stokes equation and the tracking of the particle trajectory with Langrangian approach. It was shown that the increasing of injected gas flow rate resulted in the increasing of pressure loss in the separator. This change of inner pressure had an effect on an aspect of the fluid flow in the separator. Particle movement was determined by fluid flow in the separator and was fully depended on a diameter of particles under the fixed flow rate. Increasing of injected gas flow rate was led to an increasing of the trace of particle, so the particles moved to the lower part of the separator. For this reason, the minimum diameters of the particles were decreased and increased the separation rate under the fixed particle diameter. In conclusion, the changes of injected gas flow rate have an important factor to the fluctuation of the fluid flow field and particle trajectory in the separator.