• 한국가시화정보학회:학술대회논문집
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• 2005.12a
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• pp.50-53
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• 2005

The turbulent flow around a sphere was investigated in a streamwise meridian plane using two experimental techniques: smoke-wire flow visualization in wind tunnel at Re=5,300 and PIV measurements in a circulating water channel at Re=7,400. The smoke-wire visualization shows flow separation points near an azimuthal angle of $90^{\circ}$, recirculating flow, transition from laminar to turbulent shear layer, evolving vortex roll-up and fully turbulent eddies in the sphere wake. In addition, the mean flow pattern extracted by particle tracing method in water tunnel at Re= 14,500 reveals two distinct comparable toroidal(not closed) vortices in the recirculation region. The mean velocity field measured using a PIV technique demonstrates the detailed wake configuration of close symmetric recirculation and near-wake configuration with two toroidal vortices, reversed velocity zone and vorticity contours.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.1
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• pp.34-49
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• 1998

In this study, turbulent flows in a grooved channel are numerically investigated by Large Eddy Simulation (LES). Especially, a parametric study is carried out to study effects of length and depth of a groove on large-scale flow structures. For one test case, comparison of LES results with those of DNS reveals a good agreement even though the number of grid points of LES is only 6.5% of that of DNS. This confirms that LES is a suitable tool for a parametric study of turbulent flows. The subsequent parametric study using LES shows that the large-scale turbulent structures are significantly affected by the geometry of the groove. Especially, when the length of the groove is short such that the recirculation region occupies the entire groove, the turbulent flow in the groove becomes very weak in both mean and fluctuation quantities.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.377-382
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• 2001

A suboptimal control law in turbulent pipe flow is derived and tested. Two sensing variables ${\partial}p/{\partial}{\theta}\;|_w\;and\;{\partial}{\upsilon}_{\theta}/{\partial}r\;|_w$ are applied with two actuations ${\phi}_{\theta}$ and ${\phi}_r$. To test the suboptimal control law, direct numerical simulations of turbulent pipe flow at $Re_r=150$ are performed. When the control law is applied, a $13{\sim}23%$ drag reduction is achieved. The most effective drag reduction is made at the pair of ${\partial}{\upsilon}_{\theta}/{\partial}r\;|_w$ and ${\theta}_r$. An impenetrable virtual wall concept is useful for analyzing the near-wall suction and blowing. The virtual wall concept is useful for analyzing the near-wall behavior of the controlled flow. Comparison of the present suboptimal control with that of turbulent channel flow reveals that the curvature effect is insignificant.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.10 s.241
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• pp.1083-1091
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• 2005

Turbulent flow around a rotating circular cylinder is investigated by Direct Numerical Simulation. The calculation is performed at three cases of low Reynolds number, Re=161, 348 and 623, based on the cylinder radius and friction velocity. Statistically strong similarities with fully developed channel flow are observed. Instantaneous flow visualization reveals that the turbulence length scale typically decreases as Reynolds number increases. Some insight into the spacial characteristics in conjunction with wave number is provided by wavelet analysis. The budget of dissipation rate as well as turbulent kinetic energy is computed and particular attention is given to the comparison with plane channel flow.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.21-27
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• 2010

The flow characteristics on a supersonic inlet with bleeding system by changing angles of attack and channel length conditions are studied by computational 3D turbulent flow analysis. A compressible upwind flux difference splitting Navier-Stokes method with $k-{\omega}$ turbulence model is used to analysis the inlet flowfield. More non-uniform flowfields are shown at the AIP when angle of attack becomes bigger and bigger. These non-uniform flowfield works the performance aggravating factors of the supersonic engine. Non-uniform flowfield by changing channel length at the various angle of attack are investigated.

• Advances in aircraft and spacecraft science
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• v.6 no.1
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• pp.19-30
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• 2019

Two- and three-dimensional turbulent airflows in a 9-degrees-bent channel are studied numerically. The inner surfaces of upper and lower walls are parallel to each other upstream and downstream of the bend section. The free stream is supersonic, whereas the flow at the channel exit is either supersonic or subsonic depending on the given backpressure. Solutions of the Reynolds-averaged Navier-Stokes equations are obtained with a finite-volume solver ANSYS CFX. The solutions reveal instability of formed shock waves and a flow hysteresis in considerable bands of the free-stream Mach number at zero and negative angles of attack. The instability is caused by an interaction of shocks with the expansion flow formed over the convex bend of lower wall.

• International Journal of Air-Conditioning and Refrigeration
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• v.15 no.1
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• pp.10-16
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• 2007

Surface heat transfer of a fully developed turbulent air flow in a $45^{\circ}$ inclined ribbed square duct with two and four heating walls was experimentally investigated, at which the experimental works were performed for Reynolds numbers ranging from 7,600 to 24,900. The pitch-to-rib height ratio, p/e was kept at 8 and rib-height-to-channel hydraulic diameter ratio, $e/D_h$ was kept at 0.0667. The channel length-to-hydraulic diameter ratio, $L/D_h$ was 60. The heat transfer coefficient values were decreased with the increase in the number of heating walls. Results of this investigation could be used in various applications of internal channel turbulent flow involving roughened walls.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.6
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• pp.514-520
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• 2005

Surface heat transfer of a fully developed turbulent air flow in a $45^{\circ}$ inclined ribbed square duct with two and four heating walls was experimentally investigated, at which the experimental works were peformed for Reynolds numbers ranging from 7,600 to 26,000. The pitch-to-rib height ratio, p/e, was kept at 8 and rib-height-to-channel hydraulic diameter ratio, $e/D_h$ was kept at 0.0667. The channel length-to-hydraulic diameter ratio, $L/D_h$ was 60. The heat transfer coefficient values were decreased with the increase in the number of heat-ing walls. Results of this investigation could be used in various applications of internal channel turbulent flow involving roughened walls.

• Journal of Korea Water Resources Association
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• v.30 no.3
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• pp.201-210
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• 1997

To analyze the flow through open-channel constrictions using $\kappa$-$\varepsilon$ turbulence mode, a numerical model is developed. The simulated results agree well with existing experimental data which attributes to the adequate input of turbulent eddy-viscosity by turbulence model. A stream function and velocity distributions enable the analysis of flow characteristics at the downstream of constriction. Turbulent eddy viscosities over channel are spatially varied with stream pattern. For the evaluation of rapidly varied flow, the eddy-viscosity input by turbulence model is required instead of the empirical effective viscosity to solve a shallow water equation.

• Journal of computational fluids engineering
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• v.16 no.2
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• pp.49-55
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• 2011

Turbulent flows with wavy wall are simulated using Residual-based Variational Multiscale Method (RB-VMS) which is proposed by Bazilves et al(2007) as new Large Eddy Simulation methodology. Incompressible Navier-Stokes equations are integrated using Isogeometric analysis which adopt the basis function as NURBS. The Reynolds number is 6760 based on the bulk velocity and averaged channel height. And the amplitude (${\alpha}/{\lambda}$) of wavy wall is 0.05. The computational domain is $2{\lambda}{\times}1.05{\lambda}{\times}{\lambda}$ in the streamwise, wall normal and spanwise direction. Mean quantities and turbulent statistics near wavy wall are compared with DNS results of Cherukat et al.(1998). The predicted results show good agreement with reference data.