• Journal of computational fluids engineering
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• v.8 no.2
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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.

• Journal of computational fluids engineering
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• v.8 no.2
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• pp.8-15
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• 2003

Three nonlinear κ-ε models with the wall function method are applied to the fully developed turbulent flow in a triangular subchannel of a bare rod bundle. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and wall shear stress are compared in details both qualitatively and quantitatively with both each other and experimental data. The nonlinear κ-ε models by Speziale[1] and Myong and Kasagi[2] are found to be capable of predicting accurately noncircular duct flows involving turbulence-driven secondary motion. The nonlinear κ-ε model by Shih et aL.[3] adopted in a commercial code is found to be unable to predict accurately noncircular flows with the prediction level of secondary flows one order less than that of the experiment.

• Journal of computational fluids engineering
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• v.8 no.1
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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.

• Journal of computational fluids engineering
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• v.1 no.1
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• pp.47-54
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• 1996

비유선형 물체 주위의 유동은 정체유동, 경계층 박리 및 재부착, 주기적 와열의 생성등의 복잡한 유동현상이 공존한다. 이와 같은 유동의 2-방정식 난류모델을 이용한 정확한 예측은 일반적으로 불가능 하다고 인식되어 왔으나, 본 연구에서는 기존의 비교적 단순한 난류모델을 활용한 정사각주 주위의 비정상 난류유동의 예측 가능성을 체계적으로 규명하였다. 적절한 난류모델의 선정과 더불어 시간 정확도, 공간 정확도 및 대류항 처리법 등이 해석의 결과에 미치는 영향을 살펴 보았다. 기존의 표준 κ-ε모델은 정체점 주위에서 난류생성항의 과도한 예측으로 말미암아 재부착 및 와열생성의 정확한 예측이 불가능 하였으나, RNG κ-ε 모델을 사용한 경우 이와 같은 현상을 제거 할 수 있었다. 그러나 이 경우에도 예측의 정확도가 시간 증분, 격자의 크기 및 대류항 처리법 등에 영향을 받았으며, 특별히 대류항 처리법에 따라 상당히 민감하게 변하는 것을 알 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.6
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• pp.821-827
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• 2003

Fully developed turbulent flow in a square duct is numerically predicted with two nonlinear low-Reynolds-number ${\kappa}-{\varepsilon}$ models. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in detail with each other. It is found that the nonlinear low-Reynolds-number ${\kappa}-{\varepsilon}$ model adopted in a commercial code is unable to predict accurately duct flows involving turbulence-driven secondary motion with the prediction level of secondary flows one order less than that of the experiment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.8
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• pp.1150-1157
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• 2003

Nonlinear relationship between Reynolds stresses and the rate of strain of nonlinear k-$\varepsilon$models is evaluated theoretically by using the boundary layer assumptions against the turbulence-driven secondary flows in noncircular ducts and then their prediction performance is validated numerically through the application to the fully developed turbulent flow in a square duct. Typical predicted quantities such as mean axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared with available experimental data. The nonlinear k-$\varepsilon$ model 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.

• Journal of computational fluids engineering
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• v.7 no.4
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• pp.35-41
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• 2002

The projectile afterbodies for zero-lift drag reduction has been analyzed using the Navier-Stokes equations with the κ-εturbidence model. The numerical method of a second order upwind scheme has been used on an unstructured adaptive grid system. Base drag reduction methods that have been found effective on axisymmetric bodies are boattailing, base bleed, base combustion, locked vortex afterbodies and multistep afterbodies. In this paper, turbulence flow and pressure charateristics have been studied for geometries of multistep afterbodies. The important geometrical and flow parameters relevant to the design of such afterbodies have been identified by step number, length and height. The flow over multistep aftoerbodies or base have many kinds of compressible flow characteristics including expansion waves at the trailing edge, recompression waves, separation and recirculating flow in the base region, shear flow and wake flow. The numerical results have been compared and analyzed with the experimental data. The flow characteristics have been clearly shown.

• Journal of computational fluids engineering
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• v.3 no.1
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• pp.63-72
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• 1998

The numerical simulations of flowfield and pollutant dispersion over two-dimensional hills of various shapes are described. The Reynolds-averaged Wavier-Stokes equations and concentration diffusion equation based on the gradient diffusion theory have been applied to the atmospheric shear flow over the bell-shaped hills which are basic components of the complex terrain. The flow characteristics such as velocity profiles of the geophysical boundary layer, speed-up phenomena, mean pollutant concentration profiles are compared with experimental data to validate the present numerical procedure and it has been found that the present numerical results agree well with experiments and other numerical data. It has been also found that the distributions of ground level concentration are strongly influenced by the source location and height.

• Journal of computational fluids engineering
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• v.6 no.2
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• pp.40-46
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• 2001

Two-dimensional steady flowfields generated by slot injection into supersonic flow are numerically simulated by the integration of Navier-stokes equation with two-equation κ-turbulence model. High-order upwind scheme is used on unstructured adaptive meshes. The numerical results are compared with experimental data in terms of surface static pressure distributions, the length of the upstream separation region, and the height of the Mach surface for steady flowfields with a Mach number of 3.71 and a unit Reynolds number of 5.83×10/sup 6//m.

• Journal of computational fluids engineering
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• v.4 no.2
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• pp.57-66
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• 1999

Numerical Analysis has been done for the supersonic off-design jet flow due to the pressure difference between the jet and the ambient fluid. The difference of pressure generates an oblique shock or an expansion wave at the nozzle exit. The waves reflect repeatedly on the center axis and the sonic surface in the shear layer. The pressure difference is resolved across these reflected waves. In this paper, the axi-symmetric Navier-Stokes equation has been used with the κ-ε turbulence model. The second order TVD scheme with flux limiters, based on the flux vector split with the smooth eigenvalue split, has been used to capture internal shocks and other discontinuities. Numerical calculations have been done to analyze the off-design jet flow due to the pressure difference. The variation of pressure along the flow axis is compared with an experimental result and other numerical result. The characteristics of the interaction between the shock cell and the turbulence mixing layer have been analyzed.