• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.3
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• pp.280-293
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• 1998

Numerical study on turbulent and mean structures of a turbulent boundary layer with longitudinal and spanwise pressure gradient is carried out by using Reynolds-stress-model (RSM). The existence of pressure gradient in a turbulent boundary layer causes the skewing or divergence of rates of strain, which contributes to production of turbulent kinetic energy. Also, this augmentation of production due to extra rates of strain can increase the turbulent mixing and cause the anisotropy of turbulent intensities in the outer layer. This paper uses the Reynolds Stress Model to capture anisotropy of turbulent structures effectively and is devoted to compare the results computed by using RSM and the standard k-.epsilon. model with experimental data. It is concluded that the RSM can produce the more accurate predictions for capturing the anisotropy of turbulent structure than the standard k-.epsilon. model.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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• pp.467-474
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• 2004

A large-eddy simulation is performed for turbulent flow in a concentric annulus with the inner wall rotation at Re$\sub$Dh/=8900 for three rotation rates N=0.2145, 0.429 and 0.858. Main emphasis is placed on the inner wall rotation effect on near-wall turbulent structures. Near-wall turbulent structures close to the inner wall are scrutinized by computing the lower-order statistics. The anisotropy invariant map for the Reynolds stress tensor and the invariant function are illustrated to reveal the altered anisotropy in turbulent structure. Probability density functions of the splat/anti-splat process are explored to develop a sufficiently complete picture of the contributions of the flow events to turbulent production. The present numerical results show that the altered turbulent structures may be attributed to the centrifugal instability, which leads to the augmentation of sweep and ejection events.

• Journal of Mechanical Science and Technology
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• v.14 no.1
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• pp.93-102
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• 2000

The objective of the present study is to investigate the pressure-strain correlation terms of the Reynolds stress models for the three dimensional turbulent boundary layer in a $30^{\circ}$ bend tunnel. The numerical results obtained by models of Launder, Reece and Rodi (LRR) , Fu and Speziale, Sarkar and Gatski (SSG) for the pressure-strain correlation terms are compared against experimental data and the calculated results from the standard k-${\varepsilon}$ model. The governing equations are discretized by the finite volume method and SIMPLE algorithm is used to calculate the pressure field. The results show that the models of LRR and SSG predict the anisotropy of turbulent structure better than the standard k-${\varepsilon}$ model. Also, the results obtained from the LRR and SSG models are in better agreement with the experimental data than those of the Fu and standard k-${\varepsilon}$ models with regard to turbulent normal stresses. Nevertheless, LRR and SSG models do not effectively predict pressure-strain redistribution terms in the inner layer because the pressure-strain terms are based on the locally homogeneous approximation. Therefore, to give better predictions of the pressure-strain terms, non-local effects should be considered.

• Journal of the Korean Society of Safety
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• v.15 no.3
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• pp.30-39
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• 2000

The present paper deals with the numerical simulation for the spray characteristics with swirling turbulent flows and dilution flows from swirl injectors in a simplified can type of gas turbine combustor. The main objective is to investigate the characteristics of swirling turbulent flows with dilution flows and to provide the qualitative results for the spray characteristics such as the droplet distribution and Sauter Mean Diameter(SMD). The gas-phase equations based on Eulerian approach were discretized by Finite Volume Method, together with SIMPLE algorithm and the Reynolds -Stress-Model. The liquid-phase equations based on Lagrangian method were used to predict the droplet behavior. The results of preliminary test are generally in good agreement with experimental data, and show that the anisotropy exists in the primary zone due to swirl velocity and injected air from primary injector, and then gradually decays due to turbulent mixing and consequently near-isotropy occurs in the region between primary and dilution zones. For the spray characteristics, it is indicated that the swirling flows of primary jet region increase the droplet atomization. In addition, it is showed that the swirling flows at the inlet region lead the air-fuel mixture to be distributed near the igniter and can significantly affect the spray behavior in the primary jet region.

• 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.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.473-478
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• 2000

In this study, the characteristics of the three-dimensional turbulent flow in a rotating square sectioned $90^{\circ}$ bend were investigated by numerical simulation and experiment. In the experimental study, the characteristics of a developing turbulent flow are measured using hot-wire anemometer to seize the rotational effects on the flow characteristics and to compare the results of computational simulation with Reynolds stress model. Each refinement is shown to lead to an appreciable improvement in the agreement between measurement and computation.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1980-1985
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• 2003

Two nonlinear ${\kappa}-{\epsilon}$ 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 ${\kappa}-{\epsilon}$ 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 ${\kappa}-{\epsilon}$ 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.

• 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.

• 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.