• 대한기계학회논문집B
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• 제28권6호
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• pp.652-658
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• 2004

In this paper, we report the numerical and experimental solutions of the axi-symmetric flows in the axial plane driven by an impingement of fluid from the bottom wall of a circular cylinder. We managed to visualize successfully the flow pattern shown on the vertical plane through the container axis. The numerical results are shown to compare well with the experimental results for the case of infinity Rossby number. The satisfactory agreement between the two results was possible when in the numerics the free surface was treated as a solid wall so that a no-slip condition was applied on the surface. The numerical solutions reveal that inertial oscillation plays an important role at small Rossby numbers, or at a larger background rotation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1466-1471
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• 2004

In this paper, we report the numerical and experimental solutions of the axi-symmetric flows in the axial plane driven by an impingement of fluid from the bottom wall of a circular cylinder. We managed to visualize successfully the flow pattern shown on the vertical plane through the container axis. The numerical results are not show to compare well with the experimental results for the case of the Rossby number 3. Because the numerical results calculate on the assumption that vortex flows are axi-symmetric flow on the other hand real experimental results are show asymmetric flow. The numerical solutions reveal that inertial oscillation plays an important role at small Rossby numbers, or at a larger background rotation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.640-645
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• 2003

In this paper, we report the numerical and experimental solutions of the vortical flows driven by an impingement of fluid from the bottom wall of a circular cylinder. We managed to visualize successfully the flow pattern shown on the vertical plane through the container axis. The numerical results are shown to compare well with the experimental results for the case of infinity Rossby number. The satisfactory agreement between the two results was possible when in the numerics the free surface was treated as a solid wall so that a no-slip condition was applied on the surface. The numerical solutions reveal that inertial oscillation plays an important role at small Rossby numbers, or at a large background rotation.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2012년도 춘계학술대회
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• pp.289-290
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• 2012

본 연구에서는 고정식 해양구조물의 지지각으로 사용되는 원형실린더에 나선형 판을 부착하여 와류유기진동에 미치는 영향을 고찰하였다. 연구의 목적을 달성하기 위해 $Re=6.5{\times}10^3$의 균일유입유동에서 2-프레임 그레이레벨 상호상관 PIV기법을 이용한 실험적인 방법을 적용하였다. 모델의 직경은 40mm이며 후류 유동구조, 난류강도, 응력분포에 대한 통계적 유동정보를 계측하였다. 실험결과로는 원형실린더와 뱃전판을 부착한 실린더와의 비교를 통해 뱃전판의 유동특정을 평가하였으며, 뱃전판의 영향은 후류에서 와의 생성과 소멸 메커니즘의 변화에 큰 영향을 미치고 후류 칼만 와열의 안정적인 제어를 통해 와류유기진동을 억제하였다.

• 대한기계학회논문집B
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• 제29권10호
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• pp.1101-1110
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• 2005

In this paper we present the numerical results of the behavior of the horizontal vortex generated by ejecting a liquid vertically upward from an orifice into the bulk fluid above the orifice. The numerical calculation has been performed for the axi-symmetric Navier-Stokes equation. A simple flow-visualization experiment was also conducted to qualitatively verify the numerical solutions. Three cases of the flow configurations studied in this paper are; firstly, the vortex was generated without any background rotation, secondly, the vortex was made under a full background rotation, and thirdly, the vortex was made during the spin-up process such that only the region adjacent to the side wall was set into motion viewed in the inertial frame of reference. It was shown that the swirl flow at the inlet boundary affects considerably the formation and development of the vortex for the second case. In the third case, it was remarkable to see that the vortex cannot penetrate into the region near to the side wall of the tank, because of the strong swirl flow and corresponding high pressure gradient in the region.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.463-466
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• 2002

In order to examine the possibility of using a cavity as a passive device for reduction of skin friction and heat transfer, an intensive parametric study over a broad range of the cavity depth and length at different Reynolds numbers is performed for both laminar and turbulent boundary layers in the present study. Direct and large eddy simulation techniques are used for turbulent boundary layers at low and moderate Reynolds numbers, respectively. for both laminar and turbulent boundary layers over a cavity, a flow oscillation occurs due to the shear layer instability when the cavity depth and length are sufficiently large and it plays an important role in the determination of drag and heat-transfer increase or decrease. For a cavity sufficiently small to suppress the flow oscillation, both the total drag and heat transfer are reduced. Therefore, the applicability of a cavity as a passive device for reduction of drag and heat transfer is fully confirmed in the present study. Scaling based on the wall shear rate of the incoming boundary layer is also proposed and it is found to be valid in steady flow over a cavity.

• Journal of Advanced Marine Engineering and Technology
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• 제41권1호
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• pp.31-35
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• 2017

탱크선과 같은 대형 선박 내부에 설치된 펌프시스템은 펌프장의 수위와 유량 조건에 따라서 펌프 내부유동이 크게 영향을 받게 된다. 그러나, 펌프의 성능은 설계 시 일반적으로 펌프가 작동될 펌프장 환경을 고려하지 않고 펌프 자체의 성능만을 고려하여 설계하기 때문에 펌프로 유입되는 유동에 포함된 보텍스와 선회류의 영향을 받을 경우 펌프장 내에서 공기를 동반한 보텍스 및 선회류가 발생하며, 이러한 유동 환경의 영향으로 펌프의 효율저하, 진동 및 소음문제를 일으킬 수 있다. 본 연구에서는 이러한 펌프장의 운전 조건에 따른 내부유동을 검토하기 위하여 펌프장 축소모델을 설계 및 제작하여 수위에 따른 보텍스의 발생 빈도 및 형상을 기초실험을 통하여 확인하였으며, 공기를 동반하여 펌프에 흡입되는 보텍스 Class c의 경우 상대적으로 낮은 수위에서 높은 빈도로 발생하는 것을 확인하였다.

• 설비공학논문집
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• 제22권11호
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• pp.767-772
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• 2010

The incompressible viscous flow past a sphere under forced oscillation is numerically investigated at a Reynolds number of 300. The immersed boundary method is used to handle the sphere oscillating vertically to the streamwise direction. There are two important variables to characterize the oscillating state of a sphere. One is an oscillating amplitude normalized by the sphere diameter is set as a fixed number of 0.2. Another is the frequency ratio which is defined by $f_e/f_o$, where fe and fo are the excited frequency and the natural frequency of vortex shedding for the stationary sphere. In this study, three different frequency ratios of 0.8, 1.0 and 1.2 are considered. The results show a periodic flow with hairpin vortices shedding from upper and lower positions as well as vortical legs obliquely extended by oscillating motion of sphere. The enveloping vortical structure experience rupture twice in one period of oscillation. As the frequency of oscillation is increased, the vortical legs are getting shorter and eventually the hairpin vortices are much closer to the adjacent one.

• 대한조선학회논문집
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• 제40권2호
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• pp.21-27
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• 2003

The phenomena of vortex shedding around a cylinder oscillating harmonically in a fluid at rest are investigated by a two-dimensional numerical simulation of the Navier-Stokes equations. The simulation is based on a vorticity-velocity integro-differential formulation dealing with vorticity, velocity and pressure variables. Three combinations of Reynolds number(Re) and Keulegan-Carpenter number(KC) were taken to investigate the associated vortex development around the cylinder in the different flow regimes. Drag and lift forces are computed to describe their dominant frequency modulation which is related to the vortex shedding and to the harmonic motion of the cylinder.

• 한국해양공학회지
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• 제27권5호
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• pp.16-21
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• 2013

The flow around a circular cylinder advancing beneath the free surface is numerically investigated using a VOF method. The simulations cover Froude numbers in the range of 0.2~0.6 and gap ratios (h/d) in the range of 0.1~2.0, where h is the distance from the free surface to a cylinder, and d is the diameter of a cylinder at Reynolds number 180. It is observed that the vortex suppression effect and surface deformation increase as the gap ratio decreases or the Froude number increases. The most important results of the present study are as follows. The proximity of the free surface causes an initial increase in the Strouhal number and drag coefficient, and the maximum Strouhal number and drag coefficient occur in the range of 0.5~0.7. However, this trend reverses as the gap ratio becomes small, and the lift coefficient increases downward as the gap ratio decreases.