• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.3
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• pp.181-189
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• 2000

The aerodynamic characteristics of large transport vehicle has become more and more important in recent vehicle design to improve driving performance in high speed cruising and raise the product valve with regard to a comfortable driving condition. Hence, detailed knowledge of the flow field around truck coner vane is essential to improve fuel efficiency and reduce the dirt contamination on vehicle body surface. In this study, three-dimensional flow characteristics around corner vane attached to truck cabin were computed for the steady, incompressible, and high speed viscous flow, adopting the RNG k-$\varepsilon$ turbulence model. In order to investigate the influence of configuration and structure of corner vane, computations were carried out for four cases at a high Reynolds number, Re=4.1$\times$106 (based on the cabin height). The global flow patterns, drag coefficient and the distributions such as velocity magnitude, turbulent kinetic energy around the corner vane, were examined. As a result of this study, we could identify the flow characteristics around corner vane for the variation of corner vane length and width. Also, suggest the improved structure to reduce the dirt contamination in cabin side.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.407-413
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• 2011

VIC (Vortex-In-Cell) method for viscous incompressible flow is presented to simulate the wake behind a modified NACA16 foil. With uniform rectangular grid, the velocity in field is calculated using streamfunction from vorticity field by solving the Poisson equation in which FFT(Fast Fourier Transform) is combined with 2nd order finite difference scheme. Here, LES(Large Eddy Simulation) with Smagorinsky model is applied for turbulence calculation. Effective viscosity is formulated using magnitude of strain tensor(or vorticity). Then the turbulent diffusion as well as viscous diffusion becomes particle strength exchange(PSE) with averaged eddy viscosity. The well-established panel method is combined to obtain the irrotational velocity and to apply the no-penetration boundary condition on the body panel. And wall diffusion is used for no-slip condition numerical results of turbulent stresses are compared with experimental results (Bourgoyne, 2003). Before comparing process, LES(Large Eddy Simulation) SGS(Subgrid scale) stress is transformed Reynolds averaged stress (Winckelmans, 2001).

• 한국전산유체공학회:학술대회논문집
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• 1998.05a
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• pp.15-28
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• 1998

As an alternative for solving the incompressible Navier-Stokes equations, we present a vorticity-based integro-differential formulation for vorticity, velocity and pressure variables. One of the most difficult problems encountered in the vorticity-based methods is the introduction of the proper value-value of vorticity or vorticity flux at the solid surface. A practical computational technique toward solving this problem is presented in connection with the coupling between the vorticity and the pressure boundary conditions. Numerical schemes based on an iterative procedure are employed to solve the governing equations with the boundary conditions for the three variables. A finite volume method is implemented to integrate the vorticity transport equation with the dynamic vorticity boundary condition . The velocity field is obtained by using the Biot-Savart integral derived from the mathematical vector identity. Green's scalar identity is used to solve the total pressure in an integral approach similar to the surface panel methods which have been well-established for potential flow analysis. The calculated results with the present mettled for two test problems are compared with data from the literature in order for its validation. The first test problem is one for the two-dimensional square cavity flow driven by shear on the top lid. Two cases are considered here: (i) one driven both by the specified non-uniform shear on the top lid and by the specified body forces acting through the cavity region, for which we find the exact solution, and (ii) one of the classical type (i.e., driven only by uniform shear). Secondly, the present mettled is applied to deal with the early development of the flow around an impulsively started circular cylinder.

• Journal of applied mathematics & informatics
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• v.25 no.1_2
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• pp.67-83
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• 2007

The characteristics of steady two-dimensional laminar boundary layer flow of a viscous and incompressible fluid past a moving wedge with suction or injection are theoretically investigated. The transformed boundary layer equations are solved numerically using an implicit finite-difference scheme known as the Keller-box method. The effects of Falkner-Skan power-law parameter (m), suction/injection parameter ($f_0$) and the ratio of free stream velocity to boundary velocity parameter (${\lambda}$) are discussed in detail. The numerical results for velocity distribution and skin friction coefficient are given for several values of these parameters. Comparisons with the existing results obtained by other researchers under certain conditions are made. The critical values of $f_0$, m and ${\lambda}$ are obtained numerically and their significance on the skin friction and velocity profiles is discussed. The numerical evidence would seem to indicate the onset of reverse flow as it has been found by Riley and Weidman in 1989 for the Falkner-Skan equation for flow past an impermeable stretching boundary.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.20 no.3
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• pp.203-224
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• 2016

The heat and mass transfer characteristics of the unsteady hydromagnetic natural convection flow with Hall current and Soret effect of an incompressible, viscous, electrically conducting, heat absorbing and optically thin radiating fluid flow past a suddenly started vertical infinite plate through fluid saturated porous medium in a rotating environment are taken into account in this paper. Derivations of exact analytical solutions are aimed under different physical properties. The velocity, concentration and temperature profiles, Sherwood number and Nusselt number are easily examined and discussed via the closed forms obtained. Soret effect and permeability parameter tends to accelerate primary and secondary fluid velocities whereas hall current, radiation and heat absorption have reverse effect on it. Radiation and heat absorption have tendency to enhance rate of heat transfer at the plate. The results obtained here may be further used to verify the validity of obtained numerical solutions for more complicated transient free convection fluid flow problems.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.1 s.139
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• pp.1-9
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• 2005

Waterjet propulsion is widely used to thrust high speed marine vessels in excess of 30-35 knots by virtue of the high propulsive efficiency, good maneuverability, and less cavitation. From the aspect of power loss, approximately $7-9\%$ of the total power is lost in intake duct due to the flow separation, nonuniformity, etc. Thus, detail understanding of flow phenomena occurring within intake duct is essential to reduce the power loss, as well as noise and vibration. The present work solved 30 incompressible RANS equations to provide complicated viscous flow features of intake duct. The numerical results were compared with experiments and good agreements were obtained for three jet velocity ratios.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.05a
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• pp.40-45
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• 2001

Recently, the use of numerical simulation has been increased rapidly because of the development of high performance computer systems. The present study is aimed to investigate flow characteristics of a two-dimensional sharp plane. Unsteady calculation by FDM(Finite Difference Method) based upon SOLA scheme which was performed at $Re=2{\times}10^4$in viscous incompressible flow within a finite domain on the irregular grid formation. Total numbers of irregular grids are $8{\times}10^4$. The minimum grid size is 1/100 of the plane length L which is the representative length. The inclined angles of every objects are $15^{\circ}, \;30^{\circ}\;and\; 45^{\circ}.$ And, the edge angle of the plane is $30^{\circ}.$ This study discussed the flow characteristics in term of the turbulent intensity, vorticity and frequency analysis. Developed flows show that the periodic Karman vortices occur at the back of the plane.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.15-20
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• 2005

Two-dimensional incompressible Navier-Stokes flow solver is developed using SIMPLER method to study the unsteady viscous flow physics over two-dimensional ellipses. Unsteady viscous flows over various thickness-to-chord ratios of 0.6, 0.8, 1.0, and 1.2 elliptic cylinders are simulated at different Reynolds numbers of 200, 400, and 1,000. This study is focused on the understanding the effects of Reynolds number and elliptic cylinder thickness on the drag and lift forces. The present numerical solutions are compared with available experimental and numerical results and show a good agreement. Through this study, it is observed that the Reynolds number and the cylinder thickness affect not only the frequency of the force oscillations but also the mean values and the amplitudes of the total drag and lift forces significantly.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.1
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• pp.16-27
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• 2002

A level-set method is used for analyzing the behaviors of gas bubbles in two fluids incompressible viscous flow domain. The governing equations are solved by using a finite volume method. The numerical results are verified by comparing with the experimental and other computational results. Computations for the deformations and motions of one or multi-bubbles in the flow domain with the initial undisturbed free interface are conducted. It can be seen that numerical results for different surface tension and density ratio arise very different behaviors of bubbles. When bubbles rise near the free interface, the free interface gives some great influence on the behaviors of bubbles. The present results computed by a level-set method give useful information about the properties of bubble motions and deformations.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.3
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• pp.333-347
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• 2013

The present study numerically models the interaction between a regular wave and the roll motion of a rectangular floating structure. In order to simulate two-dimensional incompressible viscous two-phase flow in a numerical wave tank with the rectangular floating structure, the present study used the volume of fluid method based on the finite volume method. The sliding mesh technique is adopted to handle the motion of the rectangular floating structure induced by fluid-structure interaction. The effect of the wave period on the flow, roll motion and forces acting on the structure is examined by considering three different wave periods. The time variations of the wave height and the roll motion of the rectangular structure are in good agreement with experimental results for all wave periods. The present response amplitude operator is in good agreement with experimental results with the linear potential theory. The present numerical results effectively represent the entire process of vortex generation and evolution described by the experimental results. The longer wave period showed a different mechanism of the vortex evolution near each bottom corner of the structure compared to cases of shorter wave periods. In addition, the x-directional and z-directional forces acting on the structure are analyzed.