• The KSFM Journal of Fluid Machinery
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• v.9 no.5 s.38
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• pp.36-41
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• 2006

In the present study, a transient incompressible viscous turbulent flow is simulated for the automotive torque converter with moving mesh technique. For the analysis, entire torque converter flow passages are modeled. Computed torque ratio, capacity factor and efficiency show a good agreement with the experiment data. The flow instabilities characterized by back-flow and wake etc. appeared in some cascade passages are shown to be propagating along tangential direction. These flow patterns are mainly influenced by the pump and turbine blade passing and can't be predicted through conventional steady simulation with a mixing plane approach. The understanding of the unsteady flow characteristics in a torque converter achieved in the present study may lead to the optimal design of a torque converter.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.4
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• pp.515-521
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• 1998

In this study the mixing process of two-phase flow which makes two jets existing vlocity difference are analyzed. The primary jet is jetted on the condition of the state mixed pulverized solid pariticle with air and the velocity in the secondary jet is changed into three kinds velocities(0.60, 75m/s) The velocity vector field concentration field and turbulent properties of solid particles are measured by using 3-Dimensional Particles Dynamics Analyzer. As the velocity of secondary jet increases the solid particle recirculation zone becomes larger. Also solid particle concentration gets dense due to velocity decrement of particles.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2810-2815
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• 2008

Flow pulsation in the gap connecting with two parallel channels is investigated by RANS and URANS approaches. The two parallel channels are connected by a small channel called for a gap. The parallel channels are designed to have different cross section area with its ratio of 0.5. Computations are conducted using a CFX 11.0 code. The bulk Reynolds number is 60,000. Predicted results are compared with the previous experimental result. Mean velocity profile at the center of gap region are compared with experiments for its validation. Spectral analysis on the lateral velocity in the center of the gap is presented. Auto and cross correlation for the axial-flow velocity pattern are presented. The unsteady structure of the flow pulsation was visualized in the region of the gap in the parallel channel.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.7
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• pp.584-591
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• 2002

The objective of the present study is to develop a model to predict heat and gas flow movement by fire in a tunnel. The model includes component models such as turbulence model, combustion model, fire model, jet fan model, etc. It has been validated using the data from Memorial Tunnel Fire Ventilation Test Program. The predictions are in good quantitative agreement with the experimental data in the far-field region of the tunnel. It should be further investigated to develop models for radiation between surfaces, for composite boundary conditions for conduction and convection, and for vigorous turbulent mixing in a tunnel especially for a large size of fire.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.546-550
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• 2010

흐름과 장파에 의하여 발생되는 난류의 subgrid scale mixing effects를 고려할 수 있는 수심적분형 모형(depth-integrated model)을 제시하였다. 완전비선형의 수심적분형 모형은 약분산(weakly dispersive) 환경에서 흐름의 회전성(rotational)을 고려하도록 perturbation approach를 이용하여 유도되었다. 동일한 방법을 이용하여 수심적분형 이송확산방정식(depth-integrated scalar transport equation)을 유도하였다. 방정식은 4차정확도의 유한체적기법을 이용하여 해석하였으며, 다양한 혼합양상을 보이는 흐름에 대한 수치모의를 수행하였다.

• 한국연소학회:학술대회논문집
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• 2013.06a
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• pp.81-82
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• 2013

This study has been mainly motivated to numerically model the supercritical mixing and combustion processes encountered in the liquid propellant rocket engines. In the present approach, turbulence is represented by the standard k-e model. To account for the real fluid effects, the propellant mixture properties are calculated by using generalized cubic equation of state. In order to realistically represent the turbulence-chemistry interaction in the turbulent nonpremixed flames, the flamelet approach based on the real fluid flamelet library has been adopted. Based on numerical results, the detailed discussions are made for the effects of swirl on flame structure of supercritical kerosene liquid propellant combustion.

• Journal of Mechanical Science and Technology
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• v.19 no.12
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• pp.2245-2252
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• 2005

Thermal stratification in the branch piping of power plants can be generated by turbulent penetration or by valve leakage. In this study, a numerical analysis was performed to estimate the thermal stratification phenomenon by in-leakage in the SIS branch piping of nuclear power plant. Leakage rate, leakage area and leakage location were selected as evaluation factors to investigate the thermal stratification effect. As a result of the thermal stratification effect according to leakage rate, the maximum temperature difference between top and bottom of the horizontal piping was evaluated to be about 185K when the valve leakage rate was about 10 times as much as the allowed leakage rate. For leakage rate more than 10 times the allowed leakage rate, the temperature difference was rapidly decreased due to the increased mixing effect. In the result according to leakage area, the magnitude of temperature difference was shown in order of $3\%,\;1\%\;and\;5\%$ leakage area of the total disk area. In the thermal stratification effect, according to the leakage location, temperature difference when leakage occurred in the lower disk was considerably higher than that of when leakage occurred in the upper disk.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.77-78
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• 2011

A multi-step quasi-global mechanism is developed for the kerosene/oxygen combustion analysis including dissociation products. Reaction constants of the global reaction are determined to have agreement with experimental data. The mechanism is used for the numerical analysis of the combustion flow field of the kerosene/oxygen shear coaxial injector. The results from high-resolution numerical analysis confirmed qualitatively that the recess enhance the fuel/air mixing and combustion efficiency by the increased flow instabilities.

• Nuclear Engineering and Technology
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• v.53 no.10
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• pp.3207-3216
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• 2021

Three-dimensional structures of a vortical flow field and heat transfer characteristics in a partially blocked 7-pin fuel assembly mock-up of sodium-cooled fast reactor have been investigated through a numerical analysis using a commercial computational fluid dynamics code, ANSYS CFX. The simulation with the SST turbulence model agrees well with the experimental data of outlet and cladding wall temperatures. From the analysis on the limiting streamline at the wall, multi-scale vortexes developed in axial direction were found around the blockage. The vortex core has a high cladding wall temperature, and the attachment line has a low cladding wall temperature. The small-scale vortex structures significantly enhance the convective heat transfer because it increases the turbulent mixing and the turbulence kinetic energy. The large-scale vortex structures supply thermal energy near the heated cladding wall surface. It is expected that control of the vortex structures in the fuel assembly plays a significant role in the convective heat transfer enhancement. Furthermore, the blockage plate and grid spacer increase the pressure drop to about 36% compared to the bare case.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.199-204
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• 1996

In the present the mean temperature and the temperature fluctuation of non-isothermal parallel liquid sodium jets were measured and analyzed changing the temperature difference and mean velocity of the hot and cold sodium. The sampling frequency and sampling time were 420Hz and three seconds, respectively. The wave-form characteristics were discussed in regard to the peak-to-peak amplitudes and the periods provided by a wave analysis. And also the correlations of the temperature fluctuation in rms value and the peak amplitude are derived. The overall mean accuracy ratios of the correlations are 1.07 and 1.08 with a standard deviation of 0.17 and 0.15, respectively.