• Journal of Ocean Engineering and Technology
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• v.2 no.1
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• pp.83-89
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• 1988

정지된 유동장에 놓인 반무한 평판이 횡방향으로 갑자기 출발하는 경우에 있어서 평판의 끝에서 발생하는 보텍스의 거동을 해석적 및 수치적 측면에서 검토하였다. 해석적 방법은 단일 보텍스 모델에 근거를 두었으며, 해석결과 순환량은 시간의 1/3승, 보텍스의 중심까지의 거리는 시간의 2/3승에 비례하여 증가함을 알 수 있었다. 룬게.쿠타(Runge-Kutta)방법을 써서 분리 보텍스 모델에 따른 비선형 운동방정식의 해를 수치적으로 구했다. 수치해는 시간의 경과에 따라 해석 해에 접근하였다. 보텍스의 형상에 있어서도 실험결과와 잘 맞았다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.839-847
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• 2012

Numerical simulations for channel flows with $Re_{\tau}$ = 180, 395 and 590 have been performed to investigate the hairpin packet formation process in wall-bounded turbulent flows. Using direct numerical simulation databases, the initial flow fields are given by the conditionally averaged flow field with the second quadrant event specified at the buffer layer. By tracking the initial vortex development, the change in the initial vortex to an ${\Omega}$-shaped vortex and th generation of a secondary hairpin vortex were found to occur with time scales based on the wall units. In addition, at the time when the initial vortex has grown to the channel center, the inclination angle of the hairpin vortex packet is approximately $12{\sim}14^{\circ}$, which is similar for all three Reynolds numbers. Finally, numerical simulations of the evolution of two adjacent hairpin vortices have been performed to examine the interaction between the adjacent vortex packets.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.3
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• pp.59-65
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• 2004

In this paper a numerical study was performed for the effect of the wall curvature on the behaviors of fuel sprays impinging on the concave Surface. Actually, in the real diesel engines, a piston head has a curved shape for the purpose of the controlling the movement of fuel droplets and the mixture formation. For past decades, although many experimental and numerical works had been performed on the spray/wall impingement phenomena, the curvature effect of impinged wall was rarely investigated. The wall curvature affects on the behaviors of the secondary droplets generated by impingement and the concave wall obstructs the droplets to advance from the impinging site to outward. In present study, the simulation code was validated for the flat surface case and three cases of the different curvature were calculated and compared with the flat surface case for several parameters, such as the spray radius, the spray height and the position of vortex center of gas phase. The simulation results showed that the radial advance of the wall spray and the vortex is decreased with increasing the curvature. It was concluded that the curvature of the impinged wall significantly affects the behaviors of both the gas-phase and the droplet-phase.

• 한국전산유체공학회:학술대회논문집
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• 2003.08a
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• pp.25-30
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• 2003

The numerical simulations with unstructured mesh by cell-centered and vertex-centered approaches were performed for the quadrilateral and triangular meshes. For the 2-D incompressible supersonic vortex flow, the simulation results and the analytic solution were compared and the accuracy was assessed. The calculation efficiency was measured by the parameter defined by the consumed CPU time multiplied by absolute error, As a results, equilateral triangular mesh yielded the best accuracy and efficiency among the tested meshes.

• Journal of computational fluids engineering
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• v.9 no.1
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• pp.48-56
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• 2004

The numerical simulations with unstructured mesh by cell-centered and vertex-centered approaches were peformed for the quadrilateral and triangular meshes. For 2-D inviscid supersonic vortex flow, the simulation results and the analytic solution were compared and the accuracy was assessed. The calculation efficiency was measured by the parameter defined by the consumed CPU time multiplied by absolute error As a results, equilateral triangular mesh yielded the best accuracy and efficiency among the tested meshes. Cell-centered approach gives a little better efficiency than vertex - centered approach.