• Journal of the Korean Society of Combustion
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• v.1 no.2
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• pp.41-49
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• 1996

A numerical study is conducted to investigate the periodically unstable shock induced combustion around blunt bodies in stoichiometric hydrogen-air mixtures. Euler equations are spatially discretized by upwind-biased third order scheme and temporally integrated by Runge-Kutta method. Chemistry model used in this study involves 8 elementary kinetics steps and 7 species. At a constant Mach number, the effects of projectile size, inflow pressure and inflow temperature are examined with Lehr#s experimental condition as a reference. In addition to oscillation frequency, characteristic distances and time averaged values are found from the result to find an relation with dimensionless parameters. As a result, it is found that the effects of inflow pressure and body size are very similar and $Damk{\ddot{o}}hler$ number plays an important role in determining the instability characteristics.

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.172-176
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• 2007

In this study, the numerical model for simulation of tsunamis is constructed by using the dispersion-correction scheme, 2nd upwind scheme, dynamic linking method, and so forth. The composed numerical model is used to simulate a hitorical tsunami event. The target tsunami event is the 1983 Central East Sea Tsunami. And, the predicted run-up heights of the tsunami at Imwon port are very reasonable compared to available observed data.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.4
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• pp.511-518
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• 1986

본 연구에서는 난류모델로는 기존의 K-.epsilon.모델과 LPS방법으로 수정된 K-.epsilon. 모 델을, 수치적 Scheme으로는 Hybrid Difference Scheme과 Skew-upwind Difference Sc- heme을 사용하여 그 결과를 각각 비교하였다.

• Bulletin of the Korean Mathematical Society
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• v.48 no.4
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• pp.873-896
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• 2011

The semi-discrete central scheme and central upwind scheme use Runge-Kutta (RK) time discretization. We do the Lax-Wendroff (LW) type time discretization for both schemes. We perform numerical experiments for various problems including two dimensional Riemann problems for Burgers' equation and Euler equations. The results show that the LW time discretization is more efficient in CPU time than the RK time discretization while maintaining the same order of accuracy.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.235-238
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• 2005

The unsteady supersonic flow over two- and three-Dimensional cavities has been analyzed by the integration of unsteady Reynolds-Averaged Navier-Stokes(RANS) with the k - w turbulence model. The unsteady flow is characterized by the periodicity due to the mutual relation between the shear layer and the internal flow in cavities. Numerical method is upwind TVD scheme based on the flux vector split with the Van Leer limiters, and time accuracy is used explicit 4th stage Runge-Kutta scheme. Cavity flows are Comparison of two- and three-dimensional. The cavity has a L/D ratio of 3 for two-dimensional case. and same L/D and W/D ratio is 1 for three-dimensional case. The Mach and Reynolds numbers are held constant at 1.5 and 450000 respectively. For the three-dimensional case, the flow field is observed to oscillate in the 'shear layer mode' with a feedback mechanism that follow Rossiter's formula. On the other hand, the self-sustained oscillating flow transitions to a 'wake mode' for the two-dimensional simulation, with more violent fluctuations inside the cavity.

• Journal of computational fluids engineering
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• v.10 no.4 s.31
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• pp.51-58
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• 2005

The unsteady supersonic flow over two- and three-dimensional cavities has been analyzed by the integration of unsteady Reynolds-Averaged Navier-Stokes(RANS) with the k-$\omega$ turbulence model. The unsteady flow is characterized by the periodicity due to the mutual relation between the shear layer and the internal flow in the cavity. An explicit 4th order Runge-Kutta scheme and an upwind TVD scheme based on the flux vector split with the van Leer limiters are used for time and space discritizations, respectively. The cavity has a L/D ratio of 3 for two-dimensional case, and same L/D and W/D ratio of I for three-dimensional case. The Mach and Reynolds numbers are 1.5 and 450000 respectively. In the three-dimensional flow, the field is observed to oscillate in the 'shear layer mode' with a feedback mechanism that follows Rossiter's formula. In the two-dimensional simulation, the self-sustained oscillating flow has more violent fluctuation inside the cavity. The primary fluctuating frequencies of two- and three- dimensional flow agree very well with the 2nd mode of Rossiter's frequency. In the three-dimensional flow, the 1st mode of frequency could be seen.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.4 s.247
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• pp.320-327
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• 2006

The computations of chemically reacting laminar and turbulent flows are performed using the preconditioned Navier-Stokes solver coupled with turbulent transport and multi-species equations. A low-Reynolds number $k-\varepsilon$ turbulence model proposed by Chien is used. The presence of the turbulent kinetic energy tenn in the momentum equation can materially affect the overall stability of the fluids-turbulence system. Because of this coupling effect, a fully coupled formulation is desirable and this approach is taken in the present study. Choi and Merkle's preconditioning technique is used to overcome the convergence difficulties occurred at low speed flows. The numerical scheme used for the present study is based on the implicit upwind ADI algorithm and is validated through the comparisons of computational and experimental results for laminar methane-air diffusion flame and $ H_2/O_2$ reacting turbulent shear flow. Preconditioning formulation shows better convergence characteristics than that of non-preconditioned system by approximately five times as much.

• Journal of Mechanical Science and Technology
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• v.15 no.5
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• pp.671-680
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• 2001

Boundary condition is one of the major factors to influence the numerical stability and solution accuracy in numerical analysis. One of the most important physical boundary conditions in the flowfield analysis is the wall boundary condition imposed on the body surface. To solve a two-dimensional Euler equation, totally four numerical wall boundary conditions should be prescribed. Two of them are supplied by the flow tangency condition. The other two conditions, therefore, should be prepared additionally in a suitable way. In this paper, four different sets of wall boundary conditions are proposed and then applied to solve high-speed flowfields around a quarter circle geometry. A two-dimensional compressible Euler solver is prepared based on the finite volume method. This solver hires three different upwind schemes; Steger-Warmings flux vector splitting, Roes flux difference splitting, and Lious advection upstream splitting method. It is found that the way to specify the additional numerical wall boundary conditions strongly affects the overall stability and accuracy of the upwind schemes in high-speed flow calculation. The optimal wall boundary conditions should be also chosen very carefully depending on the numerical schemes used to solve the problem.

• Journal of Navigation and Port Research
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• v.27 no.5
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• pp.473-478
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• 2003

Numerical study was made on the flow characteristics around a circular pipeline between parallel walls. The incompressible Navier-Stokes equations were solved by using a third-order upwind differential scheme. When the distance near a wall is small enough, the vortex shedding is almost completely suppressed because of the interaction with the wall boundary layer separation. This study aims to clarify the characteristics of the vortex shedding regime as the body approaches a wall as Reynolds number varies. The feature of separated vorticity dynamics is analyzed at different conditions with particular attention to the interaction between the pipeline wake and the induced separation on the plane walls.

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.163-167
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• 2007

For numerical analysis of a tidal flow, a two-dimensional hydrodynamic model is developed by solving the nonlinear shallow-water equations. The governing equations are discretized explicitly with a finite difference leap-frog scheme and a first-order upwind scheme on adaptive hierarchical quadtree grids. The developed model is verified by applying to prediction of tidal behaviors. The calculated tidal levels are compared to available field measurements. A very reasonable agreement is observed.