• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.5
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• pp.553-559
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• 2004

Stratified flow past a three-dimensional obstacle such as a sphere has been a long-lasting subject of geophysical, environmental and engineering fluid dynamics. In order to investigate the effect of the stratification on the near wake, in particular, the unsteady vortex formation behind a sphere, numerical simulations of stratified flows past a sphere are conducted. The time-dependent Navier-Stokes equations are solved using a three-dimensional finite element method and a modified explicit time integration scheme. Laminar flow regime is considered, and linear stratification of density is assumed under Bossiness approximation. The computed results include the characteristics of the near wake and the unsteady vortex shedding. With a strong stratification, the separation on the sphere is suppressed and the wake structure behind the sphere becomes planar, resembling that behind a vertical cylinder.

• 한국전산유체공학회:학술대회논문집
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• 1997.10a
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• pp.49-54
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• 1997

Rice's monotone streamline upwind finite element method, which was proposed to treat convection-dominated flows, is applied to the linear triangular element. An alignment technique of unstructured grids with given velocity fields is used to prevent the interpolation error produced in evaluating the convection term in the upwind method. The alignment of grids is accomplished by optimizing a target function defined with the inner-product of a properly chosen side vector in the element with the velocity field. Two pure advection problems are considered to demonstrate the superiorities of the present approach in solving the convection-dominated flow on the unstructured grid. Solutions obtained with aligned grids are much closer to the exact solutions than those with initial regular grids. The capability of the present approach in predicting the appearance of the secondary vortex in the laminar confined jet impingement is shown by comparing streamlines to those produced by SIMPLE on a highly stretched grid toward the impingement plate.

• 한국연소학회:학술대회논문집
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• 2003.12a
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• pp.35-41
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• 2003

Propagation speeds of turbulent premixed flames have been measured in a pulsed-flame flow reactor which generates flames propagating in nearly isotropic turbulent flow field with U'/$S_L$ ranging from 1.2 to 5.3. The measurement involved a high-speed digital imaging at 1000 frames/second to capture the flame propagation motion. In addition to the flame speed measurements, flame perimeter ratio was measured for comparison. The observed flame propagation speed is high ranging from 5 to 20 times the laminar flame speed for the range of U'/$S_L$. The flames observed at extreme equivalence ratios exhibit intermittent propagation in that only a small fraction of ignited flame kernel resulted in full propagation of the flame. Also, at low equivalence ratios the flame speed decreased substantially even at high turbulence intensities.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.539-540
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• 2006

It is so difficult to small amounts of two or more fluid species into single in microchannel because flows are usually laminar. In this regard multilamination micro mixer including recirculation zone is presented. Alternating feed micro channels make multilamination and converging-diverging channels form recirculation zone. Multilamination with geometric focusing decreases diffusion path ana recirculation zones make vortex. In this paper flow patterns and mixing properties of multilamination micro mixer including recirculation zone were investigated by Computational Fluid Dynamics (CFD). The CFD results provided qualitative information on mixing.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.715-720
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• 2000

Stratified flow past a three-dimensional obstacle such as a sphere has been a long-lasting subject of geophysical, environmental and engineering fluid dynamics. In order to investigate the effect of the stratification on the near wake, in particular, the unsteady vortex formation behind a sphere, numerical simulations of stratified flows past a sphere are conducted. The time-dependent Navier-Stokes equations are solved using a three-dimensional finite element method and a modified explicit time integration scheme. Laminar flow regime is considered and linear stratification of density is assumed under Boussinesq approximation. The computed results include the characteristics of the near wake and the unsteady vortex shedding. With a strong stratification, the separation on the sphere is suppressed and the wake structure behind the sphere becomes planar, resembling that behind a vertical cylinder.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.10
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• pp.833-843
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• 2002

The present experimental and numerical investigations are performed for the characteristics of transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin- friction coefficients have been measured for the fully developed flow of water and glycerine-water solution (44%) with the inner cylinder rotating at speed of 0∼600 nm, respectively. The transitional flow has been examined by the measurement of pressure losses to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients. The occurrence of transition has been checked by the gradient changes of pressure losses and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.685-693
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• 1990

The heat transfer coefficients were calculated numerically to see the effects of radiation around the porous medium put on the flat plate at a distance from the leading edge of flat plate for the two-dimensional laminar flows. To verify the analytical model developed and invoke the heat/mass transfer analogy, an experiment was carried out using naphthalene sublimation technique. From the effects of the wake, Sherwood number is maximum around the region where the porous medium is attached. The theoretical results correspond well with the experimental results at small Darcy number. Permeability of ceramic blocks used for experiment was also measured and the Forchheimer equation is applicable in our measurement range.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.1 s.232
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• pp.63-70
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• 2005

The main objective of the present study is to predict characteristics of three dimensional pulstitile flow by location of stenosis in blood vessel with the second order bifurcation. The present study simulates the incompressible non-Newtonian laminar blood flows using a Fluent V. 6.0. The Carreau model is employed as the constitutive equation for blood. The numerical simulation carried out at five cases without and with symmetry or asymmetry stenosis. It is found that the no stenosis and stenosis before first bifurcation do not have influence on flow at second bifurcated blood vessel. However, the stenosis after first biburcation has effect on flow at second bifurcated blood vessel.

• 한국전산유체공학회:학술대회논문집
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• 2002.05a
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• pp.23-28
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• 2002

TNumerical simulations of the supersonic impinging jet flows are carried out using the 3D Navier-Stokes code. This paper is focuses on the unsteady flow features associated with stagnation bubbles and other oscillatory behavior. The 3D code was validated by reproducing the results of Lamont's experiments. Computation is carried out for the cases in which the unsteadiness of the plate shock has been observed experimentally. The computational results confirm the oscillatory feature in several kHz. Unsteady calculation with algebraic turbulence model is also performed. It is found that the laminar and turbulent results have some discrepancy in the transient period. However, both of them reveal the oscillatory behavior with similar frequency.

• Journal of computational fluids engineering
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• v.12 no.4
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• pp.61-67
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• 2007

Numerical simulation of laminar flow over two spheres in a side-by-side arrangement is carried out to investigate the effect of the inter-sphere spacing on the flow characteristics. The Reynolds numbers considered are 100, 250, and 300, covering the steady axisymmetric, steady planar-symmetric, and unsteady planar-symmetric flows in the case of a single sphere. Results show that the drag and lift coefficients and wake structures are significantly modified depending on both the Reynolds number and the spacing between the spheres. At Re=100, the flow is steady planar-symmetric irrespective of the spacing, but it shows some variation according to the spacing at Re=250 and 300. That is, the flow maintains planar symmetry of the single-sphere wake at large spacings, while it loses the symmetry at small spacings due to the generation of new asymmetric vortical structures. It is also shown that the drag and lift coefficients generally increase with decreasing inter-sphere spacing because the high pressure region is formed near the gap between the spheres.