• Proceedings of the Korean Nuclear Society Conference
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• 1998.05a
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• pp.463-468
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• 1998

수직 관다발형 비등관에서의 밀도파 진동 및 유동 폭주형 이상유동 불안정성을 해석하기 위하여 선형화 기법 및 D-partition 방법론에 근거한 해석 코드(ALFS)를 개발하고 기존 실험자료 분석을 통해 코드의 예측 성능을 평가하였다. 그 결과 이상유동이 평형상태에 있는 것으로 가정하는 가장 단순한 모델인 HEM은 전반적으로 유동 불안정성 발생 시점의 열출력을 실험치보다 약 20% 정도 낮게 예측하였으며, 이상 유동의 속도 및 온도의 비평형 상태를 고려하는DEM과 DNEM에 의한 예측 결과는 7∼15%의 평균 오차 범위에서 실험 자료를 예측하는 것으로 나타났다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.7
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• pp.89-96
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• 2006

The combustion temperature in gas generator should be kept below around 1,000K to avoid any possible thermal damages to turbine blade by adopting either fuel rich or oxidizer rich combustion. Thus, non-equilibrium chemical reaction dominates in the gas generator. Meanwhile, Kerosene is a compounded fuel mixed with various types of hydrocarbon elements and difficult to model the chemical kinetics. This study focus to model the non-equilibrium chemical reaction of kerosene/LOX with detailed kinetics developed by Dagaut using PSR(Perfectly stirred reactor) assumption. Also, droplet evaporation time is taken into account by calculating for the residence time of droplet and by decoupling reaction temperature from the reactor temperature. In Dagaut’s surrogate model for kerosene, chemical kinetics of kerosene consists of 1592 reaction steps with 207 chemical species. The comparison of calculation results with experimental data could provide very reliable and accurate numbers in the prediction of combustion gas temperature, species fraction and other gas properties.

• 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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.143-147
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• 2007

Kerosene and diesel are compounded fuels with various types of hydrocarbon elements and difficult to model the chemical kinetics. This study focuses on the prediction of the non-equilibrium reaction of fuel-rich combustion with detailed kinetics developed by Dagaut using PSR(perfectly stirred reactor) assumption. In Dagaut's surrogate model for kerosene and diesel, chemical kinetics consists of 2352 reaction steps with 298 chemical species. Also, Frenklach's soot model was implemented along with detailed kinetics to calculate the gas properties of fuel rich combustion efflux.

• Journal of computational fluids engineering
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• v.17 no.4
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• pp.69-74
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• 2012

Hypersonic flowfields over a sphere is calculated by using a nonequilibrium flow solver. The flow solver features a two-temperature model and finite rate chemical reaction models to describe nonequilibrium thermochemical processes. For the purpose of validation, the calculated shock stand-off distance is compared with the experimental data which is measured in a ballistic range facility. The present nonequilibrium calculation well reproduced the experimental shock stand-off distance in the cases where the experimental flowfields are expected to be nearly equilibrium, as well as in the cases to be nonequilibrium flowfields in the velocity range 4000 to 5500 m/s.

• Journal of computational fluids engineering
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• v.20 no.3
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• pp.1-7
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• 2015

When the steam is used as working fluid in fluid machinery, different from other gases as air, phase transition (steam condensation) can occur and it affects not only the flow fields, but also machine performance & efficiency. Therefore, considering phase transition phenomena in CFD calculation is required to achieve accurate prediction of steam flow and non-equilibrium wet-steam model is needed to simulate realistic steam condensing flow. In this research, non-equilibrium wet-steam model is implemented on in-house code(T-Flow), the flow fields including phase transition phenomena in convergent-divergent nozzle are studied and compared to results of advance researches.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.7 s.262
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• pp.620-627
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• 2007

In this paper, we adapt a modified internal energy non-equilibrium first-order extrapolation thermal boundary condition to the thermal lattice Boltzmann model (TLBM). This model is the double populations approach to simulate hydrodynamic and thermal fields. The bounce-back boundary condition which is a traditional boundary condition of lattice Boltzmann method has only a first order in numerical accuracy at the boundary and numerical instability. A non-equilibrium first-order extrapolation boundary condition has been verified to be of better numerical stability than the bounce-back boundary condition and this boundary condition is proved to be of second-order accuracy for the flat boundaries. The two-dimensional natural convection flow in a square cavity with Pr=0.71 and various Rayleigh numbers are simulated. The results are found to be in good agreement with those of previous studies.

• Proceedings of the Korea Water Resources Association Conference
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• 1995.05a
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• pp.15-26
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• 1995

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.2
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• pp.367-373
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• 2007

The present study investigates numerically nonequilibrium energy transfer between electrons and phonons in metal thin films irradiated by ultrashort pulse lasers and it also provides the temporal and spatial variations of electron and phonon temperatures using the well-established two-temperature model(TTM) on the basis of the Boltzmann transport equation(BTE). This article predicts the crater shapes in gold film structures, and compares the results by using two-dimensional energy transport equation. From the results, it is found that nonequilibrium energy transfer between electrons and phonons takes place, and the equilibrium time increases with the increase of laser fluence. On the other hand, above threshold fluence the ablation time doesn't change nearly with increasing fluences. Compared with one-dimensional TTM, it also reveals that the temporal distributions of electron and phonon temperatures at the top surface estimated by using two-dimensional TTM have a similar tendency. The results show that two-dimensional TTM can simulate the crater shape of metals during the irradiation of femtosecond pulse lasers and the absorbed energy is propagated to z-direction faster than to r-direction.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05a
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• pp.531-537
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• 1995

본 논문에서는 증기폭발의 전파과정을 해석하기 위한 수학적 모델을 제시하였다. 이 모델은 용융물, 용융파편, 그리고 냉각재 기상과 액상 둥 4상 유체의 2차원적인 천이거동을 지배방정식 및 관련상관식의 수치적 해를 구함으로써 증기폭발의 전파속도 및 폭발압력 등을 예측할 수 있다. 모델에 사용된 주요 상관식은 용융물 분쇄, 냉각재 상변화, 에너지 교환, 그리고 운동량 교환함으로 구성되어 있다. 냉각재의 상태를 결정하는데 있어서 냉각재의 기상과 액상 사이의 열역학적인 비평형을 허용할 수 있도록 냉각재의 상태방정식을 구성하였다. 주석/물의 증기폭발에 대한 예제계산을 수행한 결과 폭발의 전파속도 및 압력 등에 있어서 합당한 것으로 밝혀졌다. 또한 중요한 초기변수(중기 분율, 용융물 분율) 및 관련상관식에 대한 민감도 분석을 수행함으로써 모델개선을 위한 중요인자를 제시하였다.