• Journal of Environmental Science International
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• v.2 no.1
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• pp.17-26
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• 1993

The layer that is directly influenced by ground surface is called the atmospheric boutsdary layer in comparison with the free atmosphere of higher layer. In the boundary layer, the changes of wind, temperature and coefficient of turbulent diffusion in altitude are large and have great influences an atmospheric diffusion. The purpose of this paper is to express the structure and characteristics of development of mixed layer by using laboratory experiment and numerical simulation. Laboratory experiment using water tank are performed that closely simulate the process of break up of nocturnal surface inversion above heated surface and its phenomena are analyzed by the use of horizontally averaged temperature which is observed. The result obtained from the laboratory experiment is compared with theoretical ones from ; \textsc{k}-\varepsilon numerical model. The results are summarized as follows. 1) The horizontally averaged temperature was found to vary smoothly with height and the mixed layer developed obviously being affected by the convection. 2) The mean height of mixed layer may be predicted as a function of time, knowing the mean initial temperature gradient. The experimental values are associated well with the theoretical values computed for value of the universal constant $C_r$= 0.16, our $C_r$ value is little smaller than the value found by Townsend and Deardoru et al.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.385-390
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• 2003

Shape of a multi-blades centrifugal fan is optimized by response surface method based on three-dimensional Navier-Stokes analysis. For numerical analysis, Reynolds-averaged Wavier-Stokes equations with standard $k-{\varepsilon}$ turbulence model are transformed into non-orthogonal curvilinear coordinate system, and are discretized with finite volume approximations. Due to the large number of blades in this centrifugal fan, the flow inside of the fan is regarded as steady flow by introducing the impeller force models for economic calculations. Optimizations with and without constraints are carried out. Design variables, location of cur off, radius of cut off, expansion angle of scroll and width of impeller were selected to optimize the shapes of scroll and blades. Data points for response evaluations were selected by D-optimal design, and linear programming method was used for the optimization on the response surface. As a main result of the optimization, the efficiency was successfully improved. The correlation of efficiency with relative size of inactive zone at the exit of impeller is discussed as well as with average momentum fluxes in the scroll.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.34.2-34.2
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• 2010

We built 7 potential extra-terrestrial planets including the full 3D Earth model with various surface types and 6 planet models, each with uniform surface characteristics. The surface types include ice, tundra, forest, grass, ground and ocean. We then imported these 7 planets into integrated ray tracing(IRT) model to compute their disk averaged spectra and to understand the spectral behavior depending on the geometrical view, illumination phase and seasonal change. The IRT computation show that the 6 planets with uniform surfaces exhibit clear spectral differences from that of the Earth. We then built a phase and seasonal DAS database for the 6 uniform surface planets and used them for parametric spectral decomposition technique to derive the Earth DAS. This computation resulted in the first potential solution to the surface type ratio of the Earth compared to the measured earth surface type ratio. The computational details and the implications are discussed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.31-34
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• 2012

Numerical simulations of the steady and unsteady state were conducted for a coaxial swirl injector with Kerosene fuel. Non-premixed equilibrium model based on chemical equilibrium assumption was used as turbulence-chemistry interaction model. As an equations of state, SRK(Soave-Redlich-Kwong) EOS was applied to deal with the behavior of real fluid in a high pressure condition. Through the steady and unsteady computations, mean values of steady and time-averaged unsteady state were compared on the temperature and OH mass fraction and it was shown that the flame structure of steady state was different to that of time-averaged unsteady state.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.3
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• pp.87-99
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• 1994

Reynolds Averaged Navier-Stokes equations are solved numerically for the computation of turbulent flow around a Wigley double model. A second order finite difference method is applied for the spatial discretization on the nonstaggered grid system and 4-stage Runge-Kutta scheme for the numerical integration in time. In order to increase the time step, residual averaging scheme of Jameson is adopted. Pressure field is obtained by solving the pressure-Poisson equation with the appropriate Neumann boundary condition. For the turbulence closure, 0-equation turbulence model of Baldwin-Lomax is used. Numerical computation is carried out for the Reynolds number of 4.5 million. Comparisons of the computed results with the available experimental data show good agreements for the velocity and pressure distributions.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.3
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• pp.595-609
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• 2015

The wake characteristics of Contra-Rotating Propeller (CRP) were investigated using numerical simulation and flow measurement. The numerical simulation was carried out with a commercial CFD code based on a Reynolds Averaged Navier-Stokes (RANS) equations solver, and the flow measurement was performed with Stereoscopic Particle Image Velocimetry (SPIV) system. The simulation results were validated through the comparison with the experiment results measured around the leading edge of rudder to investigate the effect of propeller operation under the conditions without propeller, with forward propeller alone, and with both forward and aft propellers. The evolution of CRP wake was analyzed through velocity and vorticity contours on three transverse planes and one longitudinal plane based on CFD results. The trajectories of propeller tip vortex core in the cases with and without aft propeller were also compared, and larger wake contraction with CRP was confirmed.

• The KSFM Journal of Fluid Machinery
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• v.15 no.4
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• pp.19-26
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• 2012

In this paper, a parametric study on ribs which are installed in an equilateral triangular internal cooling channel is presented. The numerical analysis of the flow structure and heat transfer characteristics is performed using three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model. The numerical results are obtained at Reynolds number, 20,000. The parametric study is performed for the parameters, the angle of a rib, rib pitch-to-hydraulic diameter ratio, rib width-to-hydraulic diameter ratio, and rib height-to-hydraulic diameter ratio. The computational results are validated with the experimental data for area-averaged Nusselt number.

• Interaction and multiscale mechanics
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• v.5 no.1
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• pp.27-40
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• 2012

The two-dimensional incompressible flow of a linear viscoelastic fluid we considered in this research has rapidly oscillating initial conditions which contain both the large scale and small scale information. In order to grasp this double-scale phenomenon of the complex flow, a multiscale analysis method is developed based on the mathematical homogenization theory. For the incompressible flow of a linear viscoelastic Maxwell fluid, a well-posed multiscale system, including averaged equations and cell problems, is derived by employing the appropriate multiple scale asymptotic expansions to approximate the velocity, pressure and stress fields. And then, this multiscale system is solved numerically using the pseudospectral algorithm based on a time-splitting semi-implicit influence matrix method. The comparisons between the multiscale solutions and the direct numerical simulations demonstrate that the multiscale model not only captures large scale features accurately, but also reflects kinetic interactions between the large and small scale of the incompressible flow of a linear viscoelastic fluid.

• Journal of the Society of Naval Architects of Korea
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• v.40 no.5
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• pp.17-25
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• 2003

Velocity field behind a container ship model with a rotating propeller has been investigated using PIV (particle image velocimetry) system. Four hundred instantaneous velocity fields were measured at 4 different blade phases and ensemble-averaged to investigate the spatial evolution of vortical structure of near wake within one propeller diameter downstream. The phase-averaged mean velocity fields show the potential wake and the viscous wake formed due to the boundary layers developed on the blade surfaces. The interaction between bilge vortex developed along the hull surface and the tangential velocity component of incoming flow causes to have asymmetric flow structure in the transverse plane.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.1
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• pp.60-66
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• 2000

In order to improve cavitation characteristics for a high-speed propeller, leading edge shape of a 2-D hydrofoil is investigated numerically and experimentally. For flowfield analysis around the leading edge, the incompressible Reynolds Averaged Navier-Stokes(RANS) equation is solved using the standard $k-\varepsilon$ turbulence model and a finite volume method(FVM). The cavitation thickness, which is occurred on hydrofoil surface, is predicted using the panel code. It is shown that the calculation codes predict the experimental trend fairly well. From these results, new hydrofoils are designed