• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.729-731
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• 2008

Three-dimensional unsteady simulation using RNG $\kappa-\varepsilon$ turbulence model is used in full flow passage of model Kaplan turbine. Then the pressure pulsation is obtained. Monitoring data of pressure pulsation in the turbine is obtained through experiment and is compared with the numerical simulation. And a good coherence is shown between the simulation and the experiment. Then the regularity of the pressure pulsation s distribution and transmission in the turbine is discussed in detail.

• 한국자동차공학회논문집
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• 제11권3호
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• pp.115-123
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• 2003

With the advent of high performance computers and more efficient numerical algorithms, computational fluid dynamics(CFD) has come out as a modem alternative for reducing the use of wind tunnels test in automotive engineering. However, in spite of the fact that many competent researchers have made all their talents in developing turbulence model over since the past dozen or more years, it has been an important impediment in using the CFD effectively to design machinery and to diagnose or to improve engineering problems in the industry since the turbulence model has been acting as the Achilles' tendon in aspect of the reliability even to this time. In this study, Reynolds-averaged Wavier-Stokes equations were solved to simulate an incompressible turbulent flow around a bus-like bluff body near ground plane. In order to investigate the effect of the discretisation schemes and turbulence model on the aerodynamic forces several turbulence models with five convective difference schemes are adopted. From the results of this study, it is clear that choice of turbulence model and discretisation scheme profoundly affects the computational outcome. The results also show that the adoption of RNG $k-\varepsilon$ turbulence model and nonlinear quadratic turbulence model with the second order accurate discretisation scheme predicts fairly well the aerodynamic coefficients.

• 한국산학기술학회논문지
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• 제9권4호
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• pp.865-870
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• 2008

대형디젤 기관에서 매연배기가스에 대한 배기가스 재순환장치의 영향을 KIVA-3V 전산유체해석코드를 통해서 수치 해석적으로 연구했다. 지배방정식으로 RNG k-$\varepsilon$ 난류 모델을 이용했고, 무화, 벽 침투 그리고 매연 등의 물리적인 현상을 나타내기 위해서 TAB, Wave, Watkins-Park, Nagle-Strickland 모델이 적용되었다.

• 한국산학기술학회논문지
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• 제18권3호
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• pp.545-550
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• 2017

대동맥이나 협착된 경동맥에서는 심장수축기에 간헐적으로 난류현상이 발생하고 있으며, 혈액의 점성특성으로 인해 기존 난류모델로는 정확한 해석이 어려운 실정이다. 혈류는 점탄성 유체의 성질을 가지고 있어 유체의 전단 변형률 증가에 따라 점도가 감소하는 점탄성 유체이며, 이러한 점탄성 유체는 난류 유동시 저항 감소 현상이 발생한다. 기존의 난류해석 모델들은 점성변화가 없는 뉴턴 유체에 적합한 모델들이 대부분이기 때문에, 점탄성 유체의 저항 감소 현상을 고려한 비뉴턴 유체 해석에 적합한 난류 모델개발이 필요하다. 본 논문은 난류 모델 가운데 수렴성이 좋고 해석시간이 짧은 표준 $k-{\varepsilon}$ 모델을 기반으로 저항 완충 함수를 이용하여 비뉴턴 유체의 저항감소 현상을 해석할 수 있는 수정된 난류모델을 제시하였으며, 이를 기존 난류모델들과 비교하여 제시된 난류 모델을 검증하였다. 새로 제시된 수정된 난류모델은 벽함수 및 점성저층을 고려하지 않았기 때문에 해석시간이 대폭적으로 감소하였으며, 적은 격자수를 이용하여 효율적으로 비뉴턴 유체의 난류 현상을 해석할 수 있기 때문에 향후 혈류해석 및 점탄성유체 해석에 적용할 예정이다.

• 한국전산유체공학회지
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• 제15권3호
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• pp.9-15
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• 2010

In this study, we calculated arc discharges and flow characteristics driven by arcs in a thermal puffer chamber, which is one of most outstanding high-voltage interrupters, for understanding the complex physics and the probability of thermal breakdown. The four main parts of arc model for this virtual-reality are radiation, PTFE ablation, Cu evaporation, and turbulence. Among these important parts the turbulence model can be critical to the reliability of computation results during the whole arcing history because the plasma flow is affected by high heat energy and mass momentum. Two turbulence models, the Prandtl's mixing length model and the standard $k-\varepsilon$ model, are applied for these calculations and are compared with pressure-rise inside chamber and arc voltage between the contacts as well as flow characteristics near current zero.

• 대한토목학회논문집
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• 제28권6B호
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• pp.643-651
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• 2008

본 연구에서는 횡방향 언덕-저면의 하상형상을 갖는 개수로 흐름을 수치모의 하였다. 곡선좌표계에 대한 지배방정식을 유도하고, 난류폐합을 위해 Speziale(1987)가 제안한 비선형 $k-{\varepsilon}$ 모형을 이용하였다. 개발된 모형의 개수로 흐름에 대한 적용성 및 모형 상수의 민감도를 분석하기 위해 직사각형 개수로 흐름을 수치모의 하였다. 그 결과 모형상수 $C_D$와 $C_E$는 각각 이차흐름 강도 및 난류의 비등방성에 영향을 미치는 것으로 확인되었다. 또한 비선형 $k-{\varepsilon}$ 모형이 자유수면에서 발생되는 난류의 비등방성을 정확히 모의할 수 없는 것으로 나타났으나, 전반적인 이차흐름 분포는 비교적 잘 예측하는 것으로 확인되었다. 한편 개발된 모형을 이용하여 횡방향 하상형상을 갖는 개수로 흐름을 수치모의하고 기존의 실험 결과와 비교하였다. 그 결과 비선형 $k-{\varepsilon}$ 모형이 하상형상의 언덕과 저면에서 발생되는 상향류 및 하향류를 비교적 정확히 예측하는 것으로 나타났으며, 계산된 주흐름방향 평균유속 및 난류구조 역시 기존의 실험 결과와 잘 일치하였다. 그러나 비선형 $k-{\varepsilon}$ 모형은 하상형상의 저면을 향하는 하향류를 과소 산정하는 것으로 확인되었다.

• 한국전산유체공학회지
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• 제8권2호
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• pp.57-63
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• 2003

Two nonlinear κ-ε models with the wall function method are applied to the fully developed turbulent flow in a square duct. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in details both qualitatively and quantitatively with each other. A nonlinear κ-ε model with the wall function method capable of predicting accurately duct flows involving turbulence-driven secondary motion is presented in the present paper. The nonlinear κ-ε model of Shih et al.[1] adopted in a commercial code is found to be unable to predict accurately duct flows with the prediction level of secondary flows one order less than that of the experiment.

• 한국전산유체공학회지
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• 제8권1호
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• pp.23-29
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• 2003

Two nonlinear κ-ε models with the wall function method are applied to the fully developed turbulent flow in a square duct. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in details both qualitatively and quantitatively with each other. A nonlinear κ-ε model with the wall function method capable of predicting accurately duct flows involving turbulence-driven secondary motion is presented in the present paper. The nonlinear κ-ε model of Shih et al.[1] adopted in a commercial code is found to be unable to predict accurately duct flows with the prediction level of secondary flows one order less than that of the experiment.

• 한국전산유체공학회지
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• 제20권1호
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• pp.47-56
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• 2015

In this paper, we study the effect of various turbulence models by comparing the aerodynamic characteristics and the flow patterns computed for aircraft models. An in-house CFD solver, MSAPv, that solves the three dimensional RANS equations with the turbulence model equations is used. The turbulence models used in this study are the Spalart-Allmaras model, Menter's $k-{\omega}$ SST model, Coakley's $q-{\omega}$ model, and Huang and Coakley's $k-{\varepsilon}$ model. DLR-F6 WB and WBNP configurations are selected for the study. We concentrate on the separated flow pattern variations with the turbulence models at the wing-body junction and the wing-pylon junction as well as drag polar curves.

• 한국물환경학회지
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• 제22권1호
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• pp.159-165
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• 2006

Numerical simulation of turbulence flow in a circulating channel was performed. The RNG $k-\varepsilon$ model and Reynolds stress model of the FLUENT was used for evaluating the flow mechanisms. The simulation results were compared with the experimental data measured by a ADV (Acoustic Doppler Velocitmeter). The distribution of chironomids was analyzed by the computational results. They distributed at the region of lower velocities and lower turbulence intensity. In the case of a hemisphere structure being located on the straight section, chironomids lived in the upstream and downstream area of the hemisphere. The secondary currents also affected the distribution of chironomids. In conclusion, the computational fluid dynamic techniques can be inexpensively applied for analysing the relationship between flow characteristics and distribution of benthic macroinvertebrates.