• Journal of computational fluids engineering
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• v.3 no.1
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• pp.30-36
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• 1998

The three dimensional Navier-Stokes equations in rotational coordinate are solved using a multigrid algorithm for the calculations of turbulent flows in centrifugal compressor impellers. Some numerical studies are made in applying the multigrid algorithm for the turbulent flow calculations with the standard κ-ε equations. The present method is used to calculate the flow fields of Mizuki's B-type and Niigata Ms. 350 centrifugal compressor impellers. Fast convergent steady-state solutions are carefully examined, comparing the static pressure distributions along the impeller flow passage and also in the diffuser with experimental data. Performance of a centrifugal compressor system is also numerically validated by comparing the performances of the impeller and the diffuser individually.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.2
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• pp.133-140
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• 1984

A "two-fluid" equation model has been applied for predicting gas-solid suspension flows through a Venturi tube. In the "two-fluid"equation model, the bulk motion of the particles is considered as a continuum whose governing equation is obtained by averaging the conservation equations over a volume and expressing the equations in differential forms. Closure of the time-mean equations is achieved by modeling the turbulent correlations with an extended mixing-length theory. Proposed closure model is found to aptly simulate the dependency of the static pressure drop on the particle size, flow rate and the loading ratio.d the loading ratio.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.12
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• pp.1014-1021
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• 2009

A new eddy viscosity equation was formulated from assumption of turbulence length scale equation and specific dissipation ratio equation. Then, a set of turbulence model equations for the turbulent kinetic energy ${\kappa}$, the viscosity ${\nu}_t$, and the intermittency factor ${\gamma}$ is proposed by considering the entrainment effect. Closure coefficients are determined by experimental data and resorting to numerical optimization. Present model has been applied to compute four representative cases of free shear flows and successfully compared with experimental data. In particular, the spreading rate, the centreline mean velocity and the profiles of intermittency are calculated with improved accuracy. Also, the proposed ${\nu}_t-{\kappa}-{\gamma}$ model was applied to channel flow by considering the wall effect and the results show good agreements with the Direct Numerical Simulation data.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.439-442
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• 2002

In this study, a turbulence simulation is carried out in a suction type wind tunnel using grids, where turbulent flows with various turbulence intensity are successfully produced by the change of grid size, arrangement of grids and settling position, respectively. Response tests of rectangular cylinder models with aspect ratio of 2 and 4 are carried out in smooth flow and generated turbulent flows. Additionally, two types of fairing are considered such as right triangle and regular triangle. The effects of wind velocity fluctuations and fairing are discussed on vortex-induced oscillation.

• Journal of Mechanical Science and Technology
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• v.16 no.5
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• pp.703-709
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• 2002

In the present paper, approximate coordinate transformations for simulation of turbulent flows with wall deformation, significantly reducing computational cost with little degradation in numerical accuracy, are presented. The Wavier-Stokes equations are coordinate-transformed with an approximation of Tailor-series truncation. The performance is evaluated by performing numerical simulations of a channel flow at Re$\sub$$\tau$/ = 140 with active wall motions of η$\sub$m/$\^$+/ $\leq$5. The approximate transformations provide flow structures as well as turbulence statistics in good agreement with those from a complete transformation [Phys. Fluids 12, 3301 (2000) ] and allow 25-30% savings in the CPU time as compared to the complete one.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.762-767
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• 2001

LES formulation was applied to simulate the flow fields around rotating fan blades tested by DLR. The turbulent flows around fan blade rotating with 500 RPM were simulated and the far-field noise was exactly computed by using the Focus Williams and Hawkings equation with an inclusion of quadrapole source formulation. The dipole noise computed at the far-field by predicted drag and lift forces at steady state was in good agreement with experimental data and the dipole source was also found to be the major factor than other sound sources from unsteady calculation.

• Wind and Structures
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• v.6 no.4
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• pp.263-278
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• 2003

This study investigates the effects of a bridge deck's width-to-depth (B/H) ratio and turbulence on buffeting response and flutter critical wind speed of long-span bridges by conducting section model tests. A streamlined box section and a plate girder section, each with four B/H ratios, were tested in smooth and turbulent flows. The results show that for the box girders, the response increases with the B/H ratio, especially in the vertical direction. For the plate girders, the vertical response also increases with the B/H ratio. However, the torsional response decreases as the B/H ratio increases. Increasing the B/H ratio and intensity of turbulence tends to improve the bridge's aerodynamic stability. Experimental results obtained from the section model tests agree reasonably with the calculated results obtained from a numerical analysis.

• Journal of ILASS-Korea
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• v.11 no.1
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• pp.39-47
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• 2006

In-cylinder flows in a motored 3.5L four-valve SI engine were investigated quantitatively using three-component LDV system, to determine how engine configuration affects the flow field. The purpose of this work was to develop quantitative methods which correlate in-cylinder flows to engine performance. For this study, two distinct intake/piston arrangements were used to examine the flow characteristics. Quantification of the flow field was done by calculating two major parameters which are believed to characterize adequately in-cylinder motion. These quantities were turbulent kinetic energy(TKE) and tumble ratio in each plane at each crank angle. The results showed that in-cylinder flow pattern is dominated by the intake effects and two counter rotating vortices, developed during the intake stroke, produced relatively low tumble ratio. Therefore, the applicability of these quantities should be carefully considered when evaluating characteristics resulting from the complex in-cylinder flow motions.

• Journal of Ship and Ocean Technology
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• v.4 no.1
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• pp.11-20
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• 2000

Reynolds-averaged Navier-Stokes equations are numerically solved using a secondorder finite difference method for the analysis of turbulent flows around single and tandem hydrofoils advancing under the free surface. The location of the free surface, not known a priori, is computed from the kinematic free surface condition and the computational grid is conformed at each iteration to the free surface deformation. The eddy viscosity model of Baldwin-Lomax is employed for the turbulence closure. The method is validated through the comparision of the numerical results with the experimental data for a single hydrofoil of a Joukowski foil section. A computational study is also carried out to investigate the effect of the submergence depth and the Froude number on the lift and the drag of the hydrofoil. For tandem hydrofoils, computations are performed for several separation distances between the forward and aft foils to see the interference effect. The result shows clearly how the lift and drag change with the separation distance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1467-1475
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• 2001

In the present paper, approximate coordinate transformations for simulation of turbulent flows with active wall motions, leading to a significant reduction in the computational cost while maintaining the numerical accuracy, are presented: the Navier-Stokes equations are coordinate-transformed with an approximation of Taylor-series truncation and neglect of some less-significant terms. The performance of the proposed transformations is evaluated in simulation of the channel flow at Re$\sub$$\tau$/=140 with wall deformations of │η$\sub$m/$\^$+/ 5. The approximate transformations provide flow structures as wall as turbulence statistics in good agreement with those from a complete coordinate transformation [Phys. Fluids 12, 3301 (2000)] and allow 25-30% savings in the CPU time as compared to the complete one.