• Journal of Power System Engineering
• /
• v.16 no.2
• /
• pp.17-23
• /
• 2012

The steady three-dimensional computational thermal flow analysis using standard k-${\varepsilon}$ turbulence model was carried out to investigate the heat transfer characteristics of a cabin cooler for a commercial vehicle. The heat exchanging method of this cabin cooler is to use the cooling effect of a thermoelectric module. In view of the results so far achieved, the air system resistance of a cabin cooler is about 12.4 Pa as a static pressure, and then the operating point of a cross-flow fan considering in this study is formed in the comparatively low flowrate region. The air temperature difference obtained from the cold part of an thermoelectric module is about $26^{\circ}C$, and the cooling water temperature difference obtained from the hot part of an thermoelectric module is about $3.5^{\circ}C$.

• Journal of Power System Engineering
• /
• v.16 no.5
• /
• pp.47-54
• /
• 2012

The steady three-dimensional numerical analysis on the thermal flow using standard k-${\varepsilon}$ turbulence model was carried out to investigate the air cooling effect of a cooler on the cabin for a commercial vehicle. Here, the heat exchanging method of this cabin cooler uses the cooling effect of a thermoelectric module. In consequence, the air system resistance of a cooler within the cabin is about 12.1 Pa as a static pressure, and then the operating point of a virtual cross-flow fan considering in this study is formed in the comparatively low flowrate region. The discharging air temperature of a cooler is about $14{\sim}15^{\circ}C$. Moreover, the air cooling temperature difference obtained under the outdoor cabin temperature of $40^{\circ}C$ shows about $7{\sim}9^{\circ}C$ in a driver resting space and about $9{\sim}14^{\circ}C$ in the front of a driver's seat including the space of a driver's foot.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.03a
• /
• pp.729-731
• /
• 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.

• Journal of Power System Engineering
• /
• v.18 no.3
• /
• pp.59-65
• /
• 2014

The computational fluid dynamics was carried out to evaluate turbulent models on the swirling flow of a gun-type gas burner(GTGB) according to the mesh size. The commercial SC/Tetra software was used for a steady-state, incompressible and three-dimensional numerical analysis. In consequence, the velocity magnitude from the exit of a GTGB and the flowrate predicted by the turbulent models of MP k-${\varepsilon}$, Realizable k-${\varepsilon}$ and RNG k-${\varepsilon}$ agree with the results measured by an experiment very well. Moreover, the turbulent kinetic energy predicted by the turbulent model of standard k-${\varepsilon}$ with mesh type C only agrees with the experimental result very well along the radial distance. On the other hand, the detailed prediction of the information of swirling flow field near the exit of a GTGB at least needs a CFD analysis using a fairly large-sized mesh such as a mesh type C.

• Wind and Structures
• /
• v.17 no.4
• /
• pp.361-377
• /
• 2013

Wall functions have been widely used in computational fluid dynamics (CFD) simulations and can save significant computational costs compared to other near-wall flow treatment strategies. However, most of the existing wall functions were based on the asymptotic characteristics of near-wall flow quantities, which are inapplicable in complex and non-equilibrium flows. A modified wall function is thus derived in this study based on flow over a plate at zero-pressure gradient, instead of on the basis of asymptotic formulations. Turbulent kinetic energy generation ($G_P$), dissipation rate (${\varepsilon}$) and shear stress (${\tau}_{\omega}$) are composed together as the near-wall expressions. Performances of the modified wall function combined with the nonlinear realizable k-${\varepsilon}$ turbulence model are investigated in homogeneous equilibrium atmosphere boundary layer (ABL) and flow around a 6 m cube. The computational results and associated comparisons to available full-scale measurements show a clear improvement over the standard wall function, especially in reproducing the boundary layer flow. It is demonstrated through the two case studies that the modified wall function is indeed adaptive and can yield accurate prediction results, in spite of its simplicity.

• 한국전산유체공학회:학술대회논문집
• /
• 2003.10a
• /
• pp.43-45
• /
• 2003

Nonlinear relationship between Reynolds stresses and the rate of strain for nonlinear${\kappa}-{\varepsilon}$ turbulence models is validated theoretically by using the boundary layer assumptions against the turbulence­driven secondary flows in noncircular ducts and then the prediction performance for several nonlinear models is evaluated numerically through the application to the turbulent flow in a square duct.

• Journal of the Korean Statistical Society
• /
• v.27 no.3
• /
• pp.349-358
• /
• 1998

Consider the AR(1) model $X_{t}$=$\beta$ $X_{t-1}$+$\varepsilon$$_{t}$ where $\beta$ < 1 is an unknown parameter to be estimated and {$\varepsilon$$_{t}$} denotes the independent and identically distributed error terms with unknown common distribution function F. In this paper, a strong representation for the least absolute deviation (LAD) estimate of $\beta$ in AR(1) models is obtained under some mild conditions on F. on F.F.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2009.05a
• /
• pp.545-549
• /
• 2009

본 연구에서는 주흐름방향으로 식생 영역이 교차적으로 존재하는 개수로 흐름에 대한 3차원 수치 모의를 수행하였다. 지배방정식의 난류 폐합을 위해 $k-{\varepsilon}$ 난류모형을 이용하였다. 먼저, 하상의 일부만 식재된 부분 식생 수로를 수치모의 하고 기존의 실험 결과와 비교하였다. 그 결과 본 모형이 평균유속 분포를 매우 잘 예측하는 것으로 나타났으나, 레이놀즈응력 분포는 실험 결과에 비해 비식생영역에서는 다소 과소 산정하고 식생영역에서는 과대 산정하는 것으로 나타났다. 이는 본 모형이 등방성 모형이기 때문에 식생 경계부에서 발생되는 난류의 비등방성 효과를 정확히 예측 할 수 없기 때문인 것으로 판단된다. 또한 주흐름방향으로 식생 영역이 교차적으로 존재하는 대응 식생 수로를 수치모의하고, 계산 결과를 기존의 실험 결과와 비교하였다. 그 결과 본 모형이 대응 식생 수로에서의 유속 분포를 매우 잘 예측하는 것으로 나타났다. 또한 식생 밀도가 증가함에 따라 식생이 흐름 방향을 변화시켜 점차 만곡수로와 유사한 형태의 흐름이 형성되는 것으로 나타났다.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2003.10a
• /
• pp.11-15
• /
• 2003

In order to suppress a repulsive interfacial energy between hydrophilic clay and hydrophobic polymer matrix in preparing a polymer/clay nanocomposite, a third component of amphiphilic nature such as poly($\varepsilon$-caprolactone) (PCL) was introduced into the model system of styrene-acrylonitrile copolymers (SAN)/Na-montmorillonite. Once $\varepsilon$-caprolactone was polymerized in the presence of Na-rnontmorillonite, the successful ring-opening polymerization of $\varepsilon$-caprolactone and the well-developed exfoliated structure of PCL/Na-montmorillonite mixture were confirmed, Thereafter, SAN was melt-mixed with PCL/Na-montmorillonite nanocomposite, which resulted in that SAN matrix and PCL fraction were completely miscible to form homogeneous mixture with retention of the exfoliated state of Na-montmorillonite, exhibiting that PCL effectively stabilizes the repulsive polymer/clay interface and contributes the improvement of mechanical properties of the nanocomposites.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.6 no.4
• /
• pp.101-107
• /
• 1998

A three-dimensional multi-phase flow is simulated around a smooth tire. This simulation is conducted by solving Navier-Stokes equation with a k-$\varepsilon$ turbulent model. The numerical calculations are carried out by modeling a multi-phase free surface flow mixed with air and water at the inlet. The numerical solutions show an intuitively resonable behavior of water around a moving tire. The calculated pressure around the tire surface along the moving direction is presented. The moving velocities of the tire are chosen to be 30, 40, 60, and 70 km/h. The numerically simulated pressures around the tire are compared with existing experimental data. The comparison shows a new possible tool of analyzing a hydroplaning phenomenon for an automobile tire by means of a computational fluid dynamics.