• 대한기계학회논문집B
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• 제40권7호
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• pp.441-448
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• 2016

프로펠러에 의한 추력은 유체의 유입 속도와 익의 회전속도에 의해 생성되며 그 성능을 전진비, 추력계수, 동력계수와 같은 무차원수로 나타내고 있다. 이 연구에서 회전체의 성능을 분석하기 위한 수치적 방법으로 STL형식의 회전체 형상을 인식할 수 있는 가상경계법을 적용한 격자볼쯔만법을 제안한다. 이 가상경계법으로 프로펠러의 회전에 의한 유동을 구현하기 위해서 프로펠러의 표면 격자점에서 속도와 유동장의 격자점에서 유속의 차를 이용하여 계산한 체적력을 볼쯔만방정식의 외력항으로 적용하게 된다. 제안한 방법을 검증하기 위하여 4개의 익을 가지고 있는 프로펠러를 이용해 레이놀즈수가 100, 500, 1000이고 전진비가 0.2~1.4일 때 유동해석을 수행하였으며 그 결과로 부터 전형적인 프로펠러의 성능특성을 얻을 수 있었다. 높은 레이놀즈수와 전진비를 갖는 유동에서 해석 안정성을 확보하기 위해서는 익의 표면에 구성한 최대 격자의 크기와 유동장에 구성한 격자 크기의 비가 3 이하로 유지해야 하며 충분히 긴 후류영역을 확보할 필요가 있다.

• 한국전산유체공학회지
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• 제15권2호
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• pp.21-27
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• 2010

Immersed boundary lattice Boltzmann method (IBLBM) has been applied to simulate a turbulent flow over circular cylinder in a flow field effectively. Although IBLBM is very effective method to simulate the flow over a complex shape of obstacle in the flow field regardless of the constructed grids in the calculation domain, the results, however, become numerically unstable in high reynolds number flow. The most effective suggestion to archive the numerical stability in high Reynolds number flow is applying the multiple relaxation time (MRT) model instead of single relaxation time(SRT) model in the collision term of lattice Boltzmann equation. In the research MRT model for IBLBM was introduced and comparing the numerical results obtained by applying SRT and MRT. The hydraulic characteristic of cylinder in a flow field between two parallel plate at the range of $Re{\leqq}2000$represented and it is also compared the drag and lifting coefficients of the cylinder calculated by IBLBM with SRT and MRT model.

• 한국전산유체공학회지
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• 제16권2호
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• pp.24-29
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• 2011

Immersed boundary lattice Boltzmann method has been applied to analyze the characteristics of the self-propelled fish motion swimming robot. The airfoil NACA0012 with caudal fin stroke model was considered to examine the characteristics. The foil in steady forward motion and a combination of steady-state harmonic deformation produces thrust through the formation of a flow downstream from the trailing edge. The harmonic motion of the foil causes unsteady shedding of vorticity from the trailing edge, while forming the vortices at the leading edge as well. The resultant thrust is developed by the pressure difference formed on the upper and lower surface of the airfoil. and the time averaged thrust coefficient increases as Re increase in the region of $Re{\leqq}700$. The suggested numerical method is suitable to develop the fish-motion model to control the swimming robot, however It would need to extend in 3D analysis to examine the higher Re and to determine the more detail mechanism of thrust production.

• 대한기계학회논문집B
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• 제32권12호
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• pp.924-930
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• 2008

Immersed boundary method (IBM) is the most effective method to overcome the disadvantage of LBM (Lattice Boltzmann Method) related to the limitation of the grid shape. IBM also make LBM possible to simulate flow over complex shape of obstacle without any treatment on the curved boundary. In the research, IBLBM was used to perform LBM simulation of a flow over a moving circular cylinder to determine the flow feature and aerodynamics characteristic of the cylinder. To ascertain the applicability of IBLBM on the moving obstacle near the wall, it was first simulated for the case of the flow over a fixed circular cylinder in a channel and the results were compared against the solution of moving cylinder in the channel using IBLBM. The simulations were performed in a moderate range of Reynolds number at each moving cylinder to identify the flow feature and aerodynamic characteristics of circular cylinder in a channel. The drag and lift coefficients of the cylinder were calculated from the simulation results. We have numerically confirmed that the critical Reynolds number for vortex shedding is Re=50 and the result is the same as the case of fixed cylinder. As the cylinder approaching to a wall (${\gamma}<2.5$), the 2nd vortex is developed by interacting with the wall boundary-layer vorticity. When the cylinder is very closed to the wall, ${\gamma}<0.6$, the cylinder acts like blockage to block the flow between the cylinder and wall so that the vortex developed on the upper cylinder elongated and time averaged lifting and drag coefficients abruptly increase.

• 대한기계학회논문집B
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• 제33권2호
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• pp.107-115
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• 2009

A Computational study was carried out in order to investigate the aerodynamic characteristics of circular cylinder moving near the wavy wall at a low Reynolds number of 50. Lattice Boltzmann method was used to simulate the flow field and immersed boundary method was combined to represent the moving cylinder and wavy wall regardless of the constructed grid in the domain. The aerodynamics characteristics of the cylinder moving near the wavy wall were represented by the comparing the lifting coefficients with various altitudes (H/D) and wave length and amplitudes of wavy wall. It indicated that the twice of increasing-decreasing variations of lifting coefficient are obtained while the cylinder moves near the wavy wall. The first variation is obtained where the cylinder locates near the peak of the wavy wall. Another variation occurs when the distance to the wavy wall becomes longer after passing the peak. It was also classified that three different patterns of relation between the lifting and drag coefficient of the cylinder. However, the classification is limited to the case of the same order of altitude, amplitude and wave length of the wavy wall.