• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1444-1452
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• 1999

The turbulence structure of e. tip vortex generated by e. fixed wing was investigated with the use of two-dimensional laser Doppler velocimetry. The velocity field, composed of circumferential end axial components, was measured on the vertical section to the vortex trail, located at 2C downstream from the wing tip in the incoming flow condition of $Re=2.24{\times}10^5$. A quasi 3-dimensional measurement technique by use of 2-dimensional LDV system was suggested for Reynolds stresses and the higher moments. The validity of this technique was confirmed with the uncertainty analysis. The budget of the turbulence kinetic energy was analyzed by those results in the radial direction of the vortex core. It is resulted that the production is to be very likely balanced with the dissipation in most range of the vortex core.

• Journal of Korean Society for Atmospheric Environment
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• v.15 no.5
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• pp.639-647
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• 1999

Experimental methods of plume dispersion in convective boundary layer using a composite turbulence water tank have been established through (ⅰ) manufacturing of water tank system, (ⅱ) providing of tracer whose volatility is relatively low, (ⅲ) development of software for image processing of dispersed particles in fluid, and (ⅳ) application of appropriate similarity law. Using these methods, the vertical dispersion coefficient $$\sigma$_2$ at long distances on mesoscale and the centerline height $Z_c$ of plumes have been measured. Measurement of $$\sigma$_2$ have been validated through comparison with CONDORS field experiments, and analysed with respect to the intensity of heat flux and mechanical turbulence as well as plume release height. Downwind distance where plume center height approaches to final level has also been analysed in respect of these three parameters.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.75.2-75.2
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• 2010

We have studied the statistical properties of turbulence in molecular clouds identified in the Boston University - Five College Radio Astronomy Observatory (BU-FCRAO) Galactic Ring Survey (GRS). Toward this end, the probability density function (PDF) and velocity distribution were measured for about 50 molecular clouds. We found there exists a good correlation between the PDF width and the velocity dispersion for these molecular clouds. In order to investigate how general properties of astrophysical turbulence depends on the plasma parameters such as magnetic field strength and sonic Mach number, we performed three-dimensional MHD simulations. We then examined if the observed characteristics of interstellar turbulence are consistent with theoretical results from MHD simulations.

• 한국연소학회:학술대회논문집
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• 2003.12a
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• pp.49-56
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• 2003

Mathematical formulation of the zone conditional two-fluid model is established to consider flame-generated turbulence in premixed turbulent combustion. The conditional statistics of major flow variables are investigated to understand the mechanism of flame generated turbulence. The flow field in burned zone shows substantially increased turbulent kinetic energy, which is highly anisotropic due to reaction kinematics across thin flamelets. The transverse component of rms velocities in burned zone become larger than axial component in the core of turbulent flame brush. The major source or sink terms of turbulent kinetic energy are the interfacial transfer by the mean reaction rate and the work terms by fluctuating pressure and velocity on a flame surface.

• Journal of computational fluids engineering
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• v.7 no.1
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• pp.1-9
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• 2002

In this paper, a modification of PISO algorithm based on standard k-ε turbulence model was proposed. The numerical technique used in this research is finite volume method, hybrid scheme for discretizing convection term, Euler implicit scheme for discretizing time term, and non-staggered grid. The basic idea of the modification of PISO algorithm is to perform an additional corrector stage for turbulence kinetic energy and dissipation rate to correct the inconsistence of flow and turbulence. In order to validate this algorithm, simulation of flow around a square cylinder (Re=3000) was performed in two-dimensional case. The results obtained from the proposed scheme show better agreement with those from the experiment than using original PISO algorithm in coherent velocity field.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.47.3-47.3
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• 2019

In this talk, we present numerical simulations of driven hydrodynamic and magnetohydrodynamic (MHD) turbulence with weak/strong imposed magnetic fields. We mainly focus on turbulence driven compressively (∇ × f = 0). Our main goal is to examine how magnetic fields play a role in generating solenoidal modes in compressive turbulence. From our simulation analysis, we find that solenoidal energy densities in hydrodynamic and weak magnetic field cases are generated up to ~ 30% of total ones. On the other hand, in the case of strong magnetic fields, solenoidal energy densities are excited up to ~ 70%. To interpret the results, we further analyze vorticity (w = ∇ × u) equation and find that magnetic fields directly create solenoidal motions, and magnetic tension is most effective in this sense. In hydrodynamic simulations, however, we find that viscous dissipation provides vorticity seeds at the very early stage and they are amplified via stretching process. Lastly, in weak magnetic fields cases, we find that solenoidal motions are created by the effects of magnetic fields, viscosity, and stretching in conjunction.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.1
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• pp.40-50
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• 1994

For an accurate prediction of the temperature field induced by heated water discharged into a shallow crossflow, a two-dimensional near-field numerical model is developed. It is based on a 4-equation turbulence model in which the transport equations for mean of the temperature fluctuation squared and its dissipation rate are added to those of a 2-equation turbulence model which cannot give the information of the thermal time scale ratio. Vertical diffusion is also considered by including buoyancy production and turbulence heat flux terms. The developed model is applied to a steady flow in an open channel with simple geometry and the results are compared with existing experimental data and those of the already established 2-equation turbulence model. Numerical results of the model agree with the experimental data better than those of the 2-equation model. The present model also simulates quite adequately the physical characteristics of thermal discharge in the jet entrainment and stable regions.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2000.11c
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• pp.749-756
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• 2000

Chemical application, one of the most important crop management processes happened to cause spray drift, that would threaten farmers in field as well as dwellers in rural region. Spray drift was affected by micro-meteorological parameters. In Korea, a boom sprayer was introduced but good effects of a boom sprayer was not evaluated. A study to evaluate short distance drift characteristics of a boom sprayer in paddy fields has been undergoing and determining wind characteristics in paddy field was the main purpose of this paper. Micro-meteorological information has been pre-requisite information for evaluating drift in both long and short distances or in both theoretical and experimental ways. Wind velocity, Reynolds stresses, turbulence intensity, skewness, kurtosis etc. were evaluated with height from the ground using a 2-dimensional probe and a hot wire anemometer system.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.55.2-55.2
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• 2017

We study the effect of driving scheme on the density-magnetic field correlation. We numerically investigate how the correlation time of driving affects the correlation between density and magnetic field. We performed MHD turbulence simulation using two different driving schemes - a finite-correlated driving and a delta-correlated driving. In the former, the forcing vectors change continuously with a correlation time comparable to the large-eddy turnover time. In the latter, the direction and amplitude of driving changes in a very short time scale.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.2
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• pp.148-155
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• 1995

For an accurate prediction of the temperature Held induced by surface discharge of heated water into an ambient cross-flow field. a three-dimensional near-field numerical model using k-$\varepsilon$ turbulence clousure is developed Rather restricted as it is, the numerical results of the model agree well with the experimental data. The developed model simulates quite adequately the stratification, gravitational lateral spreading, and upward entrainment of thermal jet which cannot be simulated by a depth-integrated two-dimensional numerical model, as well as the interaction with cross-flow.