Wu-Joan Kim

A Study on a VOF Method for the Improvement of Free Surface Capturing

A new numerical scheme solving two-phase flow, the Hybrid VOF method for improved free surface capturing has been developed by combining a volume capturing VOF method with the Level-Set reinitialization procedure. For validation, the proposed method is applied to 3-D bubble rising problem, dam breaking and the free surface flow around a commercial container ship. The calculated results by using the Hybrid VOF method with the two previously applied VOF formulations are compared with available numerical and experimental data. It is found that the new method provides more reasonable results than the two previous ones.

The Comparison of Flow Simulation Results around a KLNG Model Ship

AbstractNumerical simulations have been carried out for a 138K LNG Carrier (KLNG) model ship with free surface, using WAVIS 2.0 and Fluent 6.3.26 with various   values and different grid densities. Level-set method for free surface capturing was adopted in WAVIS, while VOF has been used in Fluent. The calculated results were compar ed with the experiment data. Resistance coefficient, wave pattern, wave profile along the hull surface, axial velocity contours and transverse vectors had been analyzed. When the first   value was fixed at 60, the simulation results from both WAVIS and Fluent were impr oved as the number of grids increased. The convergence time of WAVIS was much shorter than that of Fluent. Furthermore, WAVIS predicted the velocity field and the wave pr ofile along the hull surface better than Fluent. However, Fluent gave better wave patterns. ※Keywords: WAVIS, Fluent, Level-set method, VOF, Wave pattern(파형), Velocity field(속도장) 1. 서 언 수치계산용 컴퓨터와 전산유체역학(Computational Fluid Dynamics, CFD) 기술의발달에 힘입어 많은시간과 비용이 드는 수조시험

Topological View of Viscous Flow behind Transom Stern

Viscous flows behind transom stern are analyzed based on CFD simulation results. Stern wave pattern is often complicated due to the abrupt change of stern surface curvature and flow separation at transom. When a ship advances at high speed, whole transom stern is exposed out of water, resulting in the so-called `dry transom`. However, in the moderate speed regime, stern wave development in conjunction of flow separation makes unstable wavy surface partially covering transom surface, i.e., the so-called `wetted transom`. Transom wave formation is usually affecting the resistance characteristics of a ship, since the pressure contribution on transom surface as well as the wave-making resistance is changed. Flow modeling for `wetted transom` is difficult, while the `dry transom modeling` is often applied for the high-speed vessels. In the present study CFD results from the RANS equation solver using a finite volume method with level-set treatment are utilized to assess the topology of transom flow pattern for a destroyer model (DTMB5415) and a container ship (KCS). It is found that transom flow patterns are quite different for the two ships, in conformity to the shape of submerged transom. Furthermore, the existence of free surface seems to after the flow topology in case of KCS.

Experimental Study on the Drag Reduction by Injection of Microbubble and Polymer Solution in a Water Tunnel for Water-Borne Vehicles

Experiments on the friction drag reduction by injecting microbubbles or polymer solutions have been carried out for both a flat wall and an axisymmetric body. In the first setup, the drag reduction on the flat ceiling of a water channel was measured for a fully developed turbulent channel flow by using a newly developed skin friction sensor of floating element type. The effects of key controlling parameters were investigated for higher drag reduction with varying the concentration and the injection rate of the additives. The integrated frictional drag has been reduced up to 25% with the microbubble injection and 50% with the polymer solution injection. The drag reduction for a slender axisymmetric body was also investigated in a cavitation tunnel based on the parameters obtained from the channel experiments.Copyright