• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1720-1725
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• 2004

The present study addresses a computational work to investigate the influence of a turbulent wake flow on the pressure recovery of a two-dimensional subsonic diffuser. The turbulent wake is generated by a cylinder with a small diameter, which is installed at the diffuser inlet. Computation is applied to two-dimensional steady Navier-Stokes equations. The computational results are qualitatively well compared to existing experimental data. The results show that the diffuser pressure recovery is strongly dependent on the diameter and location of the cylinder. It is found that there is a certain diameter and location of cylinder for the diffuser pressure recovery to be most enhanced. Compared with no cylinder case, the diffuser performance increases up 24%.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.27-33
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• 2009

In this paper, the flow past a rotary oscillating circular cylinder is simulated. The high-order and high-resolution numerical schemes with the characteristic boundary conditions are used for the compressible Navier-Stokes equation. The frequencies of rotating oscillation are $0.19\;{\leq}\;S_f\;{\leq}\;0.25$ for the maximum angular $\theta_{max}=10^{\circ}$ and $17^{\circ}$. The flow conditions are Mach number of 0.3 and Reynolds number of 1000. At Lock-on and Non-lock-on region which are defined by the relation between the vortex shedding frequency and the oscillating frequency, the drag and lift coefficient are analyzed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.6 s.261
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• pp.566-573
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• 2007

Flows around two oscillating cylinders in side-by-side arrangement at Re=185 are simulated using an immersed boundary method. The cylinders oscillate vertically in opposite directions in uniform cross-flow. We describe flow patterns, drag and lift forces by varying distance between two cylinders $(1.4{\leq}g{\leq}2.2,\;1.0{\leq}g{\leq}1.8)$ and oscillating frequency ratios $(f_e/f_o=0.8,\;f_e/f_o=1.0\;and\;f_e/f_o =1.2)$. Wake patterns, drag and lift coefficients are affected by both of frequency ratio and gap between two cylinders. Near wakes of each case are classified with the definition of previous studies.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.349-352
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• 2002

The time-development of the wake vortices of the unsteady viscous flow past a semicircular cylinder is simulated using the vortex particle methods for direct numerical simulations(DNS). The early wake behaviour of the flow behind an impulsively started a semicircualr cylinder is evaluated for a range of Reynolds numbers between 60 and 200 with opposite body configurations respectively. The diffusion scheme based on the particle strength exchange(PSE) is used to account far the viscous effect accurately. And the vorticity generation algorithm to enforce the no-slip boundary conditions is employed. In order to redistribute particles efficiently on the distorted Lagrangian grid the particle distribution technique is adaptively revised, while maintaining the uniform resolution. The results of the simulations are compared to other experimental results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.12 s.243
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• pp.1344-1351
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• 2005

Three-dimensional, time-dependent solutions of fluid flow past a circular cylinder with a periodic array of circular fins are obtained using an accurate and efficient spectral multidomain methodology. A Fourier expansion with a corresponding uniform grid is used along the circumferential direction. A spectral multidomain method with Chebyshev collocation is used along the r-z plane to handle the periodic array of circular fins attached to the surface of the cylinder. Unlike the flow past a circular cylinder, Second instabilities like mode A and mode B are not found in the Reynolds number range $100\~500$. It is found that three-dimensional instability of vortical structures is suppressed due to the presence of fin. The present numerical solutions report the detailed information of flow quantities near wake of finned cylinder.

• Journal of computational fluids engineering
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• v.20 no.4
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• pp.51-57
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• 2015

In the present study, two-dimensional numerical investigation of flow past a square cylinder beneath the free surface has been performed to identify the effects of presence of the free surface. An immersed boundary method was adopted for implementation of the cylinder cross-section in a Cartesian grid system. Also, a level-set method was used to capture the interface of two fluids. To prevent transition to three-dimensional flow, Reynolds number chosen for this simulation was 150. The cases for Froude number 0.2 and gap ratio(h/D) between 0.25 and 5.00 were examined. At the specific Reynolds number, we study the effects of gap ratio on flow characteristics around a square cylinder by computing flow fields, force coefficients and Strouhal number.

• Journal of the Korean Society of Visualization
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• v.8 no.4
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• pp.26-30
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• 2010

A PTV algorithm was constructed using a linear transformation, in which the merits of the conventional PIV and PTV were adopted. In PIV calculations, the obtained velocity vectors are affected by the filtering effects by its calculation principle. PTV techniques are widely used for their excellences of measuring small scaled flows, such as nano and bio flows. However, PTVs produce vector errors due to interpolation process. To overcome these problems, a hybrid PTV algorithm was constructed by combining PTVs' and PIVs' benefits using a linear transformation. The Taylor-Green vortex flows were generated for the tests of vorticity calculations. The conventional gray-level cross-correlation PIV technique and 2-Frame PTV technique were tested for the same flows for comparisons with those obtained by the constructed hybrid algorithm. The excellence of the constructed hybrid algorithm was validated through an actual experiment on the cylinder wake.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.6 s.150
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• pp.675-682
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• 2006

This study has investigated the turbulent flow around a square cylinder by using LES (large eddy simulation). Numerical simulations are performed for turbulent flow fields with Re = 22,000. The computed results are in good agreement with existing computational and experimental data. The time-averaged and phase-averaged turbulent statistics around a square cylinder are discussed. Total 20 phase bins extracted from one cycle period showed detailed wake structures of the phase-averaged flow field. The center of Karman vortex sheets did not deviated ${\pm}0.5$ from centerline of square cylinder while moving downstream.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.7
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• pp.771-779
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• 2004

Unsteady behavior of the early wake in the viscous flow field past an impulsively started semicircular cylinder is studied numerically. In this paper, we propose the hybrid diffusion scheme to simulate dynamic characteristics of wake such as a fishtail-like flapping and an alternate vortex-shedding more accurately. This diffusion scheme based on particle strength exchange is mixed with the stochastic nature of random walk method. Also, the viscous splitting algorithm which calculates convective and diffusion terms successively is applied in order to handle random walk method effectively. Consequently, the early behavior of wake due to the breakdown of symmetrical vortici balance is more practically simulated with the vortex particle method.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.1
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• pp.124-135
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• 2004

An experimental study is performed turbulent flow behind a square cylinder by using 2-D PIV technique. The Reynolds number investigated are 10.000. 30.000 and 50,000. The mean velocity vector, time mean axial velocity turbulence intensity. kinetic energy and Reynolds shear stress behind the cylinder are measured, The numerical method used this study is a CFD code, STAR-CD. The numerical results are compared with these of experimental.