• Transactions of the Korean Society of Mechanical Engineers
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• 제13권5호
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• pp.1052-1060
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• 1989

Using a vortex stretching invariant term, the two-layer k-.epsilon. model has been modified to account for the extra staining of turbulence due to the mean-flow convergence and divergence. The calculations of turbulent boundary layers in a plane of symmetry are compared for experimental cases which are an axisymmetric body at an incidence of 15.deg.. The comparisons between the calculations and experimental data show that additional modifications to the dissipation rate equation have brought the significant improvement to the prediction of plane of symmetry boundary layers in the strong mean-flow convergence and divergence.

• Journal of Korean Society for Atmospheric Environment
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• 제23권6호
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• pp.708-717
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• 2007

In the present study, one of the widely applied equations for gas-solid cyclones, Leith and Licht model, was evaluated based on the 3-D CFD technique. The initial and boundary values of radial position and tangential velocity obtain-ed from the CFD simulation enabled complete calculation of the nonlinear second differential equation. This approach showed about 30% errors between calculations with and without the second order differential term. The calculation by using the simple first order equation presented shorter times to migrate up to the inner wall of the cyclone than by the second order, which theoretically implies higher separation efficiency. Further comparison is now under evaluation in terms of the detailed grade efficiency.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.327-330
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• 2006

This paper represents the numerical analysis on effects of radius ratio in a concentric annulus with a rotating inner cylinder. The numerical model consisted of two cylinder which inner cylinder is rotating and outer cylinder is fix, and the axial direction is used the cyclic condition because of the length for axial direction is assumed infinite. The diameter of inner cylinder is assumed 86.8mm, the numerical parameters are angular velocity and radius ratio. Also, the whole walls of numerical model have no-slip and the working fluid is used water at $20^{\circ}C$. The numerical analysis is assumed the transient state to observe the flow variations by time and the 3-D cylindrical coordinate system. The calculation grid adopted a non-constant grid for dense arrangement near the wall side of cylinder, the standard $k-{\omega}$ high Reynolds number model to consider the effect of turbulence flow and wall, the fully implicit method for time term and the quick scheme for momentum equation. The numerical method is compared with the experimental results by Wereley and Lueptow, and the results are very good agreement. As the results, TVF isn't appeared when Re is small because of the initial flow instability is disappear by effect of the centrifugal force and viscosity. The vortex size is from 0.8 to 1.1 for TVF at various $\eta$, and the traveling distance for wavy vortex have the critical traveling distance for each case.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제32권10호
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• pp.754-760
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• 2008

Computation of moving interface by the level set method typically requires the reinitialization of level set function. An inaccurate estimation of level set function $\phi$ results in incorrect free-surface capturing and thus errors such as mass gain/loss. Therefore, an accurate and robust reinitialization process is essential to the simulation of free-surface flows. In the present paper, we pursue further development of the reinitialization process, which evaluates level set function directly using a normal vector on the interface without solving there-distancing equation of hyperbolic type. The Taylor-Galerkin approximation and P1P1 splitting/SUPG (Streamline Upwind Petrov-Galerkin) FEM are adopted to discretize advection equation of the level set function and the incompressible Navier-Stokes equation, respectively. Advection equation and re-initialization process of free surface capturing are validated with benchmark problems, i.e., a broken dam flow and timereversed single vortex flow. The simulation results are in good agreement with the existing results.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.568-571
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• 2008

The computation of moving interface by the level set method typically requires reinitializations of level set function. An inaccurate estimation of level set function ${\phi}$ results in incorrect free-surface capturing and thus errors such as mass gain/loss. Therefore, accurate and robust reinitialization process is essential to the free-surface flows. In the present paper, we pursue further development of the reinitialization process, which evaluates directly level set function ${\phi}$ using a normal vector in the interface without solving the re-distancing equation of hyperbolic type. The Taylor-Galerkin approximation and P1P1splitting FEM are adopted to discretize advection equation of the level set function and the Navier-Stokes equation, respectively. Advection equation of free surface and re-initialization process are validated with benchmark problems, i.e., a broken dam flow and time-reversed single vortex flow. The simulation results are in good agreement with the existing results.

• Tribology and Lubricants
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• 제29권3호
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• pp.149-159
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• 2013

In this research, the lubrication characteristics of spool valves with various cross-sectional groove shapes were studied. The validity of using the Reynolds equation for the analysis of spool valves with various groove shapes was also investigated. The cross-sectional shapes for the grooves included a triangle, square, and U shape. The characteristics of the flow in the groove were investigated using streamlines. When the number of grooves was increased, the difference between the results obtained from the Reynolds equation and those obtained from the Navier-Stokes equation increased according to the groove shape. Thus, it was found that the Navier-Stokes equation should be used to investigate the lubrication characteristics of the spool valves in those cases. Moreover, in the case where the cross section of the groove was U-shaped, the groove prevented the small eddy current from occurring in the groove. Therefore, the lateral force and friction force of the spool valve with the U-shaped groove were lower than those of the spool valves with other groove shapes.

• Water Engineering Research
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• 제2권4호
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• pp.261-268
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• 2001

This study presents the estimation of the entrainment velocity of sediment particles from the scour hole. Sediment particles are entrained from the scour hole downstream of hydraulic structures by the turbulent vortices. Mathematical form of the entrainment velocity of sediment particles from the scour hole was obtained using the impulse-momentum equation with given value of the vertical component of turbulent velocity of the line vortex. Also, its probability density distribution was obtained with the results that the probability density distribution of the vertical turbulent velocity followed the normal distribution. Experimental results of the entrainment velocity of sediment particles showed relatively good agreements with theoretical ones.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 춘계 학술대회논문집
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• pp.91-98
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• 2000

The three-dimensional unsteady compressible Full Navier-Stokes equation solver with sliding multi-block method has been applied to analyze three dimensional characteristics of the flow field and compression wave around the high speed train which Is entering into a tunnel. The numerical scheme of AF + ADI was used to efficiently solve Navier-Stokes equations in the curvilinear coordinate system. The vortex formation around the nose region was found and the generation of compression wave due to the blockage effects was observed ahead of the train in the form of plane wave. The three dimensional characteristics of the flow field compared to the analytic results were discussed in detail. The variation of pressure of tunnel wall surface and velocity profile of the train are identified as the train enters into a tunnel. The changes in aerodynamic forces and streamlines of each specific sections are also discussed and presented.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1996년도 춘계 학술대회논문집
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• pp.46-51
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• 1996

The flow field around a three dimensional minivan-like body has been simulated. This study solves 3-D unsteady incompressible Navier-Stokes equations on a non-orthogonal curvilinear coordinate system using second-order accurate schemes for the time derivatives, and third/second-order scheme for the spatial derivatives. The Marker-and-Cell concept is applied to efficiently solve continuity equation. The fourth -order artificial damping is added to the continuity equation for numerical stability. A H-H type multi-block grid system is generated around a three dimensional minivan-like body. Turbulent flows have been modeled by the Baldwin-Lomax turbulent model. The simulation shows three dimensional vortex-pair just behind body. And the flow separation is also observed the rear of the body. It has concluded that the results of present study properly agree with physical flow phenomena.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 춘계 학술대회논문집
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• pp.128-137
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• 1998

In this numerical experiment, the preconditioned compressible Navier-Stokes equation is tested to analyze the laminar spray combustion. Sprayed flow field is formulated by Eulerian-Lagrangian system for the gas and liquid phases each. DSF(Deterministic Separated Flow) model was adopted for the sprays with the vortex model to describe transients of individual droplet heating. Simplified single global reaction model approximates methanol-air reaction with and without disk flame holder. The equation system is discretized by finite difference technique and time integrated by LU-SGS. Due to greatly simplified chemical reaction mechanism and the lack of experimental evidences, most of the efforts were devoted to show the applicability and robustness of preconditioned compressible flow calculation algorithm. Computation results in qualitatively reasonable combusting flow field, hence it is believed that further refinement are required to produce quantitatively accurate solutions.