• Nuclear Engineering and Technology
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• v.29 no.4
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• pp.269-279
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• 1997

The errors associated with incorrect sampling and transport of radioactive aerosol from radwaste thermal process off-gas are analyzed and the conditions of representative sampling and correct transport of radioactive aerosol for off-gas system evaluation are discussed. An estimation method of sampling errors for individual radionuclides is proposed and applied to simulated vitrification melter aerosols. Prediction methods for particle deposition in sample transport tube under laminar as well as turbulent flow conditions are also described by example calculations with simulated incinerator off-gas From the results of example calculations and plots, instrumental and operational conditions of radioactive aerosol sampling system with minimized errors and correction methods for nonideal sampling and transport are recommended.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.999-1011
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• 1989

A consideration on the trubulence models for describing the redeveloping turbulent boundary layer beyond separation-reattachment in the flow over a backward-facing step is given through experimental and numerical studies. By considering the blance among the measured values of respective terms in the transport equations for the turbulent kinetic energy and the turbulent shear stress, the recovering process of the redeveloping boundary layer from non-equilibrium to equilibrium has been investigated, which takes place slowly over a substantial distance in the downstream direction. In the numerical study, the standard K-.epsilon. model and the Reynolds stress model have been applied to two kinds of flow regions, one for the entire downstream region after the backward-facing step and another for the downstream region after reattachment. Then the results are compared to a meaningful extent, with the experimental values of the turbulent kinetic energy k, the turbulent energy production term P, the dissipation term K-.epsilon. model, a necessity for a new modelling has been brought forward, which can be also applied to the case of the nonequlibrium turbulent flow.

• Journal of computational fluids engineering
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• v.13 no.2
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• pp.20-26
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• 2008

A numerical study is carried out to analyze the steady three-dimensional turbulent flow and convective heat transfer in a staggered pin-fin array with diamond shaped elements at various geometrical configurations. Steady Reynolds-averaged Navier-Stokes equations and energy equation are solved using a finite volume based solver. Shear stress transport (SST) model is used as turbulence closure. The computational domain is composed of one pitch of pin-fin displacement with periodic boundary conditions on the surfaces normal to the streamwise direction and the cross-streamwise direction. The numerical results for Nusselt number and friction factor are validated with experimental results. The effects of pin angle, pin height and pitch on Nusselt number, friction factor and efficiency index are investigated.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.183-184
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• 2014

The multi-environment probability density function model has been applied to simulate the turbulent stratified premixed flames. The direct quadrature method of moments (DQMOM) has been adopted to solve the transport PDF equation due to its computational efficiency and robustness. Computations are made for the non-swirling turbulent stratified premixed flames including SWB1, SWB5 and SWB9. The numerical results obtained in this study are precisely compared with experimental data in terms of axial velocity, unconditional means and conditional means for scalar field including temperature and species mass fraction.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.2
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• pp.254-263
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• 2015

In this study, numerical simulations are carried out to investigate the dynamic SGS model effects in a Kerosene-LOx coaxial swirl injector under high pressure conditions. The turbulent model is based on large-eddy simulation (LES) with real-fluid transport and thermodynamics. To assess the effect of the dynamic subgrid-scale (SGS) model, the dynamic SGS model is compared with that of the algebraic SGS model. In a swirl injector under supercritical pressure, the characteristics of temporal pressure fluctuation and power spectral density (PSD) present comparable discrepancies dependant on the SGS models, which affect the mixing characteristics. Mixing efficiency and the probability density (PDF) function are conducted for a statistical description of the turbulent flow fields according to the SGS models. The back-scattering of turbulent kinetic energy is estimated in terms of the film thickness of the swirl injector.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.7 s.250
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• pp.700-706
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• 2006

This study presents a numerical procedure to optimize the shape of dimple surface to enhance turbulent heat transfer in a rectangular channel. The response surface based optimization method is used as an optimization technique with Reynolds-averaged Wavier-Stokes analysis of fluid flow and heat transfer with shear stress transport (SST) turbulence model. The dimple depth-to-dimple print diameter ratio, channel height-to-dimple print diameter ratio, and dimple print diameter-to-pitch ratio are chosen as design variables. The objective function is defined as a linear combination of heat transfer related term and friction loss related term with a weighting factor. full factorial method is used to determine the training points as a mean of design of experiment. The optimum shape shows remarkable performance in comparison with a reference shape.

• International Journal of Automotive Technology
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• v.6 no.6
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• pp.571-577
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• 2005

Combustion of turbulent sprays in a direct injection diesel engine is modeled by the conditional moment closure (CMC) model. The CMC routines are combined with the KIVA code to provide conditional flame structures to determine mean state variables, instead of mean reaction rates. An independent transport equation is solved for each flame group with equal mass of sequentially evaporating fuel vapor. CMC calculation begins as the fuel mass for each flame group begins to evaporate with corresponding initialization conditions. Comparison is made with measured pressure traces for four operating conditions at different rpm's and injection conditions. Results show that the CMC model with multiple flame histories can successfully be applied to ignition and mixing-controlled combustion phases of a diesel engine.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.229-232
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• 2008

This study presents a numerical procedure to optimize the shape of stepped circular pin-fins to enhance turbulent heat transfer. The KRG method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer with shear stress transport turbulent model. The objective function is defined as a linear combination of heat transfer and friction loss related terms with a weighting factor. Ten training points are obtained by Latin Hypercube Sampling for two design variables. Optimum shape has been successfully obtained with the increased objective function.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.229-232
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• 2008

This study presents a numerical procedure to optimize the shape of stepped circular pin-fins to enhance turbulent heat transfer. The KRG method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer with shear stress transport turbulent model. The objective function is defined as a linear combination of heat transfer and friction loss related terms with a weighting factor. Ten training points are obtained by Latin Hypercube Sampling for two design variables. Optimum shape has been successfully obtained with the increased objective function.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.23-26
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• 2002

An evaluation of one algebraic and two one-equation eddy viscosity-transport turbulence closure models as implemented to the CFDS(Characteristic Flux Difference Splitting) scheme is presented for the efficient computation of the turbulent flow. Comparisons of Baldwin-Lomax model as algebraic turbulence model and Baldwin-Barth and Spalart-Allmaras model as one-equation turbulence model are presented for three test cases for 3-dimensional flow. The numerical result of the CFDS schem is examined through comparison with the experimental data.