• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.12
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• pp.970-976
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• 2008

Characteristics of methane turbulent non-premixed flame have been studied experimentally in coflow jets with initial temperature variation. The results showed that the premixed flame model and the large-scale mixing model for turbulent flame stabilization were effective for methane fuel considered initial temperature variation. Especially, the premixed flame model has been improved by considering nitrogen dilution for the liftoff height of turbulent lifted flame. In estimating blowout velocity and the liftoff height at blowout with the premixed flame model and the large-scale mixing model, the two turbulent models were excellently correlated by considering the effect of physical properties and buoyancy for the initial temperature variation.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.2
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• pp.254-263
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• 2015

In this study, numerical simulations are carried out to investigate the dynamic SGS model effects in a Kerosene-LOx coaxial swirl injector under high pressure conditions. The turbulent model is based on large-eddy simulation (LES) with real-fluid transport and thermodynamics. To assess the effect of the dynamic subgrid-scale (SGS) model, the dynamic SGS model is compared with that of the algebraic SGS model. In a swirl injector under supercritical pressure, the characteristics of temporal pressure fluctuation and power spectral density (PSD) present comparable discrepancies dependant on the SGS models, which affect the mixing characteristics. Mixing efficiency and the probability density (PDF) function are conducted for a statistical description of the turbulent flow fields according to the SGS models. The back-scattering of turbulent kinetic energy is estimated in terms of the film thickness of the swirl injector.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1399-1409
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• 1999

It is known that previous models are unsatisfactory in predicting adverse pressure gradient turbulent flows. In the present paper, a revised low Reynolds number $k-{\varepsilon}$ model is proposed. In this model, a newly developed term is added lo the dissipation rate equation. In order to reflect appropriate effects for an adverse pressure gradient. The added tenn is derived by considering the distribution of mean velocity and turbulent properties in the turbulent flow with, adverse pressure gradient. The new $k-{\varepsilon}$ model was applied to calculations of flat plate flow with adverse pressure gradient, conical diffuser flow and backward facing step flow. It was found that the three numerical results showed better agreement than other models compared with DNS results and experimental ones.

• 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
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• v.19 no.3
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• pp.741-750
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• 1995

The turbulent buoyancy-driven flow in 2-dimensional enclosed cavities heated from the vertical side is numerically calculated for both cases of a Rayleigh number of 5*10$^{10}$ for air and 2.5*10$^{10}$ for water. Three different turbulence models are considered : standard k-.epsilon. model of Ozoe and low-Reynolds-number model of Lam and Bremhorst, and another low-Reynolds-number model of Davidson. The results indicate that the use of low-Reynolds number models is recommended for the indoor airflow computation, and the results from Davidson model are reasonably close to the reported experimental data. A sensitivity study shows that the amounts of wall-heat transfer and the velocity profiles with the Lam and Bremhorst model largely depend on the choice of the wall function for .epsilon..

• 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.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.598-603
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• 2003

A CFD analysis has been performed to investigate turbulent heat transfer in a triangular rod bundle with a pitch-to-diameter ratio(P/D) of 1.06. Anisotropic turbulence models predicted the turbulence-driven secondary flow in the triangular subchannel and the distributions of time mean velocity and temperature showing significantly improved agreement with the measurements over the linear standard ${\kappa}-{\varepsilon}$. The anisotropic turbulence models predicted turbulence structure in large flow region fairly well but could not predict the very high turbulent intensity of azimuthal velocity observed in narrow flow region(gap).

• Nuclear Engineering and Technology
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• v.36 no.2
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• pp.153-164
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• 2004

A computational fluid dynamics (CFD) analysis has been performed to investigate the turbulent flow and heat transfer in a triangular rod bundle with pitch-to-diameter ratios (P/D) of 1.06 and 1.12. Anisotropic turbulence models predicted the turbulence-driven secondary flow in a triangular subchannel and the distributions of the time mean velocity and temperature, showing a significantly improved agreement with the measurements from the linear standard $k-{\epsilon}$ model. The anisotropic turbulence models predicted the turbulence structure for a rod bundle with a large P/D fairly well, but could not predict the very high turbulent intensity of the azimuthal velocity observed in the narrow flow region (gap) for a rod bundle with a small P/D.