• Journal of the Society of Naval Architects of Korea
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• v.57 no.2
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• pp.96-103
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• 2020

The new geometric disturbance is proposed to control the flow around the bluff body. The new geometry is characterized by the variable pitch which is applied on the Helically Elliptic Twisted (HET) cylinder. The performance of the HTE geometry as a biomimetic passive flow control was confirmed by Jung and Yoon (2014). The Large Eddy Simulation (LES) is used for the evaluation of the flow control performance of the Variable Pitch HTE (VPHTE) cylinder at Reynolds number (Re) of 3000 corresponding to the subcritical regime. The circular and HTE cylinders are also considered to compare the performance of the VPHTE cylinder at the same Re. The VPHTE cylinder gives the smallest values of the force coefficients than the circular and HTE cylinders. The drag and lift coefficients of the VPHTE cylinder are about 15.2% and 94.0% lower than those of the circular cylinder, respectively. Especially, the VPHTE cylinder achieves about 2.3% and 30.0% reduction of the drag coefficient and the root mean square of the lift coefficient than the HTE cylinder, respectively. Furthermore, The VPHTE cylinder forms more elongated and stabilized separated shear layer than the circular cylinder, which supports the reduction of the force coefficients.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.2
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• pp.69-78
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• 2009

Cavitating flow simulation is of practical importance for many hydraulic engineering systems, such as pump, turbine, nozzle, injector, etc. In the present work, a solver for cavitating flow has been developed and applied to simulate the flows past axisymmetric cylinders. Governing equations are the two-phase Navier-Stokes equations, comprised of continuity equation of liquid and vapor phase. The momentum equation is in the mixture phase. The solver employed an implicit, dual time, preconditioned algorithm in curvilinear coordinates. Computations were carried out for three axisymmetric cylinders: hemispherical, ogive, and caliber-0 forebody shape. Then, the present calculations were compared with experiments and other numerical results to validate the present solver. Also, the code has shown its capability to accurately simulate the re-entrant jet phenomena and ventilated cavitation. Hence, it has been found that the present numerical code has successfully accounted for cavitating flows past axisymmetric cylinders.

• Journal of the Society of Naval Architects of Korea
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• v.35 no.4
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• pp.1-10
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• 1998

This paper presents a vorticity-based numerical method for analyzing an incompressible Newtonian viscous flow around an impulsively started cylinder. The Navier-Stockes equations have a natural Helmholtz decomposition. The vorticity transport equation and the pressure equation are derived from this decoupled form. The associated boundary conditions are dynamic for the vorticity and pressure variables representing the coupling relation between them and the force balance on the wall. The various numerical treatments for solving the governing equations are introduced. According to Wu et al.(1994), the boundary conditions are decoupled, keeping the dynamic relation between vorticity and pressure. The vorticity transport equation is formulated by FVM and TVD(Total Variation Diminishing) scheme is used for the convection term. An integral approach similar to the panel method is used to obtain the velocity field for a given vorticity field and the pressure field, instead of the conventional differential approaches. In the numerical process, the structured grid is generated. The results are compared to existing numerical and analytic results for the validity of the present method.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.6
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• pp.750-757
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• 2016

This study presents the wave run-up height around single and multiple surface-piercing cylinders according to wave period and steepness. In order to simulate 3D incompressible viscous two-phase turbulent flow, the present study employed a volume of fluid (VOF) method with realizable $k-{\varepsilon}$ turbulence model based on commercial Computational Fluid Dynamics (CFD) software, "STAR-CCM". The wave periods at model scale were 1.269s and 1.692s for a single cylinder and 1.716s for multiple cylinders. In each case, wave steepness of has 1/30 and 1/16 were used, respectively. Consequently, the results for wave run-up height with regard to wave steepness and period were compared with those of relevant previous experimental studies. The numerical simulation results showed a good qualitative agreement with experiments.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.2 s.152
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• pp.119-129
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• 2007

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.177-184
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• 2009

Cavitating flow simulation is of practical importance for many engineering systems, such as marine propellers, pump impellers, nozzles, injectors, torpedoes, etc. The present work has focused on the simulation of cavitating flow past cylinders with strong side flows. The governing equation is the Navier-Stokes equation based on the homogeneous mixture model. The momentum and energy equation is in the mixture phase while the continuity equation is solved liquid and vapor phase, separately. An implicit dual time and preconditioning method are employed for computational analysis. For the code validation, the results from the present solver have been compared with experiments and other numerical results. A fairly good agreement with the experimental data and other numerical results have been obtained. After the code validation, the strong side flow was applied to include the wake flow effects of the submarine or ocean tide.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.149-154
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• 2009

The cavitating flow simulation is of practical importance for many engineering systems, such as marine propellers, pump impellers, nozzles, injectors, torpedoes, etc. The present work has focused on the simulation of cavitating flow past cylinders with strong side flow. The governing equation is the Navier-Stokes equation based on homogeneous mixture model. The momentum and energy equation is in the mixture phase while the continuity equation is solved liquid and vapor phase, separately. An implicit dual time and preconditioning method are employed for computational analysis. The results from the present solver have been in a fairly good agreement with the experimental data and other numerical results. After the code validation the strong side flow was applied to include the wake flow effect of the submarine.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.1
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• pp.82-90
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• 2000

An experimental study has been carried out at circulating water channel to investigate the non-breaking and breaking waves generated by a submerged circular cylinder steadily moving under the free surface. Free surface profiles and pressure distributions on cylinder surface were measured at various submerged depths of cylinder. They were complemented by the measurements of velocities, head losses and turbulence intensities in the wakes of body and "breaker". Part 1 of this three-part paper describes the experimental arrangement and the patterns of wave profile and pressure distribution at various depths of submergence. These databank contributions are of special interest in traditional ship hydrodynamics. In Part 2, special focuses are made to elucidate the viscous and turbulent aspects of flow field. Finally Part 3 will deal with the visualization of instantaneous vortical flow to study the mutual interaction between vorticies shedded from the free-surface and the cylinder using a Particle Image Velocimetry.

• 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.8
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• pp.724-732
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• 2007

Flow patterns in the presence of two identical nearby circular cylinders at Re=100 were numerically studied. We considered all possible arrangements of the two circular cylinders in terms of the distance between the two cylinders and the inclination angle with respect to the direction of the main flow. Eight distinct flow patterns were identified based on vorticity contours and streamlines, which are Base-Bleed, Biased-Base-Bleed, Shear-Layer-Reattachment, Induced-Separation, Vortex-Impingement, Flip-Flopping, Modulated Periodic, and Synchronized-Vortex-Shedding. Collecting all the numerical results, we propose a general flow pattern diagram for flows past two nearby cylinders. The perfect geometrical symmetry implied in the flow configuration allows one to use this diagram to distinguish flow patterns in the presence of two identical circular cylinders arbitrarily positioned in physical space with respect to the main flow direction.