• Transactions of the Korean Society of Mechanical Engineers
• /
• v.12 no.5
• /
• pp.1158-1174
• /
• 1988

A numerical technique is developed for the solution of fully developed turbulent recirculating flow in the passage of variable area using the non-orthogonal coordinate transformation. In the numerical analysis, primitive pressure-velocity finite difference equations were solved by SIMPLER algorithm with 2-equation turbulence model and algebraic stress model (ASM). QUICK scheme on the differencing of convective terms which is free from the inaccuracies of numerical diffusion has been applied to the variable grids and the results compared with those from HYBRID scheme. In order to test the effect of streamline curvatures on turbulent diffusion Lee and Choi streamline curvature correction model which has been obtained by modifying the Leschziner and Rodi's model is testes. The ASM was also employed and the results are compared to those from another turbulence model. The results show that difference of convective differencing schemes and turbulence models give significant differences in the prediction of velocity fields in the expansion region and outlet region of the combustor, however show little differences in the parallel flow region.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.2 no.1
• /
• pp.38-50
• /
• 1994

To improve the efficiency of internal combustion engines, it is necessary to understand mixed air-fuel in-cylinder flow processes accurately at intake and compression strokes. There is experimental and numerical methods to analyse in-cylinder flow process. In numerical method, standard $k-{\varepsilon}$ model with wall function was mostly adopted in in-cylinder flow process. But this type model was not efficiently predicted in the near wall region. Therefore in the present study, low Reynolds number $k-{\varepsilon}$ model was adopted near the cylinder wall and standard $k-{\varepsilon}$ model in other region. Also QUICK scheme was used for convective difference scheme. This study takes axisymmetric reciprocating model engine motored at 200rpm with a centrally located valve, incorporated 60 degree seat angie, and flat piston surface excluding inlet port. Because in-cylinder flow processes are undergoing unsteady and compressible, averaged cylinder pressure and inlet velocity at arbitrary crank angle are determined from thermodynamic analytic method and incylinder states at that crank angle are iteratively determined from the numerical analytic method.

• Wind and Structures
• /
• v.15 no.5
• /
• pp.409-421
• /
• 2012

In this paper, the method of introducing additional source/sink terms in the turbulence and momentum transport equations was applied to appropriately model the effect of the tree canopy. At first, the new additional source term for the turbulence frequency ${\omega}$ equation in the SST k-${\omega}$ model was proposed through theoretical analogy. Then the new source/sink term model for the SST k-${\omega}$ model was numerically verified. At last, the proposed source term model was adopted in the wind environment optimal design of the twin high-rise buildings of CABR (China Academy of Building Research). Based on the numerical simulations, the technical measure to ameliorate the wind environment was proposed. Using the new inflow boundary conditions developed in the previous studies, it was concluded that the theoretically reasonable source term model of the SST k-${\omega}$ model was applicable for modeling the tree canopy flow and accurate numerical results are obtained.

• Journal of the korean society of oceanography
• /
• v.32 no.2
• /
• pp.75-84
• /
• 1997

Relation between the length scale and the wall proximity function in the Mellor-Yamada level 2.5 turbulence closure model has been investigated through various experiments using a range of wall proximity functions. The model performance has been evaluated quantitatively by comparing with laboratory data for wind-driven flow (Baines and Knapp, 1965) and for open-channel flows without and with adverse wind action (Tsuruya, 1985). Comparison shows that a symmetric wall proximity function used by Blumberg and Mellor(1987) gives rise to current profiles with better accuracy than asymmetric wall proximity functions considered. It is noted that in modelling homogeneous flows the length scale 1= 0.31${\|}$z${\|}$(1+z/h) can be used with tolerable accuracy.

• 한국전산유체공학회:학술대회논문집
• /
• 2000.10a
• /
• pp.15-24
• /
• 2000

The transient response of an airfoil to a rapidly deploying spoiler is numerically investigated using the turbulent compressible Navier-Stokes equations in two dimensions. Algebraic Baldwin-Lomax model, Wilcox $\kappa-\omega$ model, and SST $\kappa-\omega$ turbulence model are used to calculate the unsteady separated flow due to the rapid spoiler deployment. The spoiler motion relative to a stationary airfoil is treated by an overset grid hounded by a Dynamic Domain-Dividing Line which has been devised by the authors. The adverse effects of the spoiler influenced by the spoiler location and the hinge gap are expounded. The numerical results are in reasonably good agreement with the existing experimental data.

• Journal of computational fluids engineering
• /
• v.8 no.2
• /
• pp.57-63
• /
• 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.

• 한국전산유체공학회:학술대회논문집
• /
• 2005.10a
• /
• pp.179-182
• /
• 2005

We have developed a numerical scheme to reproduce the unsteady flows with cavitation by the finite-difference method. The evolution of cavitation is represented by the source/sink of vapor phase in the incompressible liquid flow. The pressure-velocity coupling is based on the fractional-step method for incompressible fluid flows, in which the compressibility is taken into account through the low Mach number assumption. We applied our method for the cavitating flows in a two-dimensional cascade, which approximates the portion near the tip of inducer in liquid-fuel engine. Particular attention was focused on the influence of turbulence model in this report. Using an eddy viscosity model, although it was not an optimized one for our purpose, the agreement with the experimental observation was improved.

• Journal of computational fluids engineering
• /
• v.21 no.4
• /
• pp.78-84
• /
• 2016

In this paper, turbulence models for considering roughness in the open source code(OpenFOAM) was investigated. Wall function in the RANS(Reynolds-averaged Navier - Stokes) turbulence model was modified considering roughness on the flat plate by using roughness function. Correlation between the first layer height in the CFD model and roughness height of the plate was observed, and the most proper roughness function, and the first layer height from the plate wall in the CFD analysis was suggested in this paper.

• 한국연소학회:학술대회논문집
• /
• 2004.06a
• /
• pp.75-82
• /
• 2004

The conditional moment closure(CMC) model has been implemented in context with the unstructured-grid finite-volume method which efficiently handle the physically and geometrically complex turbulent reacting flows. The validation cases include a turbulent nonpremixed $CO/H_2/N_2$ Jet flame and a turbulent nonpremixed $H_2/CO$ flame stabilized on an axisymmetric bluff-body burner. In terms of mean flame field, minor species and NO formation, numerical results has the overall agreement with expermental data. The detailed discussion has been made for the turbulence-chemistry interaction and NOx formation characteristics as well as the comparative performance for CMC and flamelet model.

• 한국연소학회:학술대회논문집
• /
• 2012.11a
• /
• pp.33-35
• /
• 2012

This study has been mainly motivated to numerically model the supercritical mixing and combustion processes encountered in the liquid propellant rocket engines. In the present approach, turbulence is represented by the extended k-e model. To account for the real fluid effects, the propellant mixture properties are calculated by using generalized cubic equation of state. In order to realistically represent the turbulence-chemistry interaction in the turbulent nonpremixed flames, the flamelet approach based on the real fluid flamelet library has been adopted. Based on numerical results, the detailed discussions are made for the effects of swirl number on flame structure of supercritical kerosene/LOx double swirl coaxial injector.