• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.142-147
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• 2005

A numerical study of evaluation of turbulence models for thermal striping phenomenon is performed. The turbulence models chosen in the present study are the two-layer model, the shear stress transport (SST) model and the V2-f model. These three models are applied to the analysis of the triple jet flow with the same velocity but different temperature. The unsteady Reynolds-averaged Navier-Stokes (URANS) equation method is used together with the SIMPLE algorithm. The results of the present study show that the temporal oscillation of temperature is predicted only by the V2-f model, and the accuracy of the mean velocity, the turbulent shear stress and the mean temperature is a little dependent on the turbulence model used. The the two-layer model and the SST model shows nearly the same capability of predicting the thermal striping and the amplitude of the temperature fluctuation is predicted best by the V2-f model.

• 한국해양학회지
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• v.30 no.1
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• pp.13-26
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• 1995

In this paper three turbulence models including two-equation model by Blumberg and Mellor (1987), one-equation model with mixing length formula of Blackadar's (1962), and zero-equation model of Prandtl's (1925) were compared in homogeneous, unstratified channel flows. Steady flows which a steep-sided trapezoidal trench with uniform discharge, tidal flow and steady wind-driven flow in finite channels are considered in detail. Steady flows in a trench and tidal flows in a finite channel were reproduced fairly accurately and there was virtually no difference among results of three turbulence models. However, In case of steady wind-driven flow only two-equation model reproduced the important features of experimental data. the other two models underestimated the surface velocity. In tidal and wind-driven flows with negligibly small adjective and diffusive effects, the two-equation model gives rise to parabolic profile of eddy viscosity with maximum at the mid0depth, and the one and zero equation model based on Blackadar formula linear profile with maximum at the surface.

• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.90-95
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• 1998

The two-dimensional incompressible and compressible Navier-Stokes codes are developed for the computation of the viscous turbulent flow over high-lift airfoils. Incompressible code using pseudo-compressibility and dual-time stepping method involves a conventional upwind differencing scheme for the convective terms and LU-SGS scheme for time integration. Compressible code also adopts an FDS scheme and LU-SGS scheme. Several two-equation turbulence models (the standard $k-{\varepsilon}$ model, the $k-{\omega}$ model. and $k-{\omega}$ SST model) are evaluated by computing the flow over single and multi-element airfoils. The compressible and incompressible codes are validated by computing the flow around the transonic RAE2822 airfoil and the NACA4412 airfoil, respectively. Both the results show a good agreement with experimental surface pressure coefficients and velocity profiles in the boundary layers. Also, the GA(W)-1 single airfoil and the NLR7301 airfoil with a flap are computed using the two-equation turbulence models. The grid systems around two- and three-element airfoil are efficiently generated using Chimera grid scheme, one of the overlapping grid generation methods.

• Journal of computational fluids engineering
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• v.10 no.4 s.31
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• pp.1-11
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• 2005

A numerical study of the evaluation of turbulence models for thermal striping phenomenon is performed. The turbulence models chosen in the present study are the two-layer model, the shear stress transport (SST) model and the V2-f model. These three models are applied to the analysis of the triple-jet flow with the same velocity but different temperatures. The unsteady Reynolds-averaged Navier-Stokes (URANS) equation method is used together with the SIMPLEC algorithm. The results of the present study show that the temporal oscillation of temperature is predicted by the SST and V2-f models, and the accuracy of the mean velocity, the turbulent shear stress and the mean temperature is a little dependent on the turbulence model used. In addition, it is shown that both the two-layer and SST models have nearly the same capability predicting the thermal striping, and the amplitude of the temperature fluctuation is predicted best by the V2-f model.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.4
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• pp.220-227
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• 2015

Complex thermal hydraulic characteristics exist inside the reactor because the reactor internals consist of fuel assembly, internal structures and so on. In this study, to examine the effect of Reynolds-Averaged Navier-Stokes (RANS)-based two-equation turbulence models in the analysis of flow distribution inside a 1/5 scaled-down APR+, simulation was performed using the commercial computational fluid dynamics software, ANSYS CFX R.13 and the predicted results were compared with the measured data. It was concluded that reactor internal flow pattern was locally different depending on the turbulence models. In addition, the prediction accuracy of k-${\varepsilon}$ model was superior to that of other two-equation turbulence models and this model predicted the relatively uniform distribution of core inlet flow rate.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.3
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• pp.307-316
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• 2012

Numerical simulations of 3D aircraft configurations are performed in order to understand the effects of turbulence models on the prediction of aircraft's aerodynamic characteristics. An in-house CFD code that solves 3D RANS equations and two-equation turbulence model equations are used. The code applies Roe's approximated Riemann solver and an AF-ADI scheme. Van Leer's MUSCL extrapolation with van Albada's limiter is also adopted. Various versions of Menter's $k-{\omega}$ SST turbulence models as well as Coakley's $q-{\omega}$ model are incorporated into the CFD code. Menter's $k-{\omega}$ SST models include the standard model, the 2003 model, the model incorporating the vorticity source term, and the model containing controlled decay. Turbulent flows over a wing are simulated in order to validate the turbulence models contained in the CFD code. The results from these simulations are then compared with computational results from the $3^{rd}$ AIAA CFD Drag Prediction Workshop. Numerical simulations of the DLR-F6 wing-body and wing-body-nacelle-pylon configurations are conducted and compared with computational results of the $2^{nd}$ AIAA CFD Drag Prediction Workshop. Aerodynamic characteristics as well as flow features are scrutinized with respect to the turbulence models. The results obtained from each simulation incorporating Menter's $k-{\omega}$ SST turbulence model variations are compared with one another.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.1
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• pp.40-50
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• 1994

For an accurate prediction of the temperature field induced by heated water discharged into a shallow crossflow, a two-dimensional near-field numerical model is developed. It is based on a 4-equation turbulence model in which the transport equations for mean of the temperature fluctuation squared and its dissipation rate are added to those of a 2-equation turbulence model which cannot give the information of the thermal time scale ratio. Vertical diffusion is also considered by including buoyancy production and turbulence heat flux terms. The developed model is applied to a steady flow in an open channel with simple geometry and the results are compared with existing experimental data and those of the already established 2-equation turbulence model. Numerical results of the model agree with the experimental data better than those of the 2-equation model. The present model also simulates quite adequately the physical characteristics of thermal discharge in the jet entrainment and stable regions.

• Water Engineering Research
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• v.3 no.4
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• pp.247-258
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• 2002

This paper presents a non-isotropic turbulence modeling of flows over bedforms. The Reynolds stress model is used for the turbulence closure. In the model, Launder, Reece, and Rodi's model and Hanjalic and Launder's model are employed f3r the pressure strain correlation term and the diffusion term, respectively. The mean flow and turbulence structures are simulated and compared with profiles measured in the experiments. The numerical solutions from two-equation turbulence models are also provided for comparisons. The Reynolds stress model yields the separation length of eddy similar to the other numerical results. Using the developed model, the resistance coefficients are also estimated for the flows at different Froude numbers. Karim's (1999) relationship is used to determine the bedform geometry. It is found that the values of the form drag and the skin friction are very similar to those obtained by the other turbulence models. meaning higher values of the form drag and lower values of the skin friction compared with the empirical formulas.

• 한국전산유체공학회:학술대회논문집
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• 1999.05a
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• pp.85-89
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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 at the center axis and on the sonic surface in the shear layer, and the pressure difference is resolved across these waves interacted with the turbulence mixing layer. In this paper, the axi-symmetric Navier-Stokes equation has been used with two equation $k-{\varepsilon}$ turbulence closure model. The second order TVD scheme with flux limiters, based on the flux vector split by the smooth eigenvalue split, has been used to capture internal shocks and other discontinuities. The correction term for the compressible flow and the damping function are used in the turbulence model. 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.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.172-177
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• 2004

In the present work, we have interests on the modification of parallel implemented with MPI(Message Passing Interface) programming method, 3-Dimensional, unsteady, incompressible Navier-Stokes equation solver to analyze the low-Reynolds number flow In order to accurate calculation aerodynamic coefficients in low-Reynolds number flow field, we modified the two-equation turbulence model. This paper describes the development and validation of a new two-equation model for the prediction of flow transition. It is based on Mentor's low Reynolds $\kappa-\omega$ model with modifications to include Total Stresses Limitation (TSL) and Separation Transition Trigger (STT)