• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.307-310
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• 2002

A two-dimensional numerical method for inviscid two-fluid flows with evolution of density interface is developed, and an initially stationary two-dimensional fluid sheet surrounded by another fluid is studied. The Interface between two fluids is modeled as a vertex sheet, and the flow field u÷th the evolution of interface is solved by using vortex-in-cell/front-tracking method. The edge of the sheet Is pulled back into the sheet due to surface tension and a blob is formed at the edge. This blob and fluid sheet are connected by a thin neck. In the inviscid limit, such process of the blob and neck formation is examined in detail and their kinematic characteristics are summarized with dimensionless parameters. The edge recedes at $V=1.06({\sigma}/{\rho}h)^{0.5}$ and the capillary wave Propagating into the fluid sheet must be considered for bettor understanding of the edge receding.

• 한국해양환경ㆍ에너지학회지
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• 제10권2호
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• pp.107-111
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• 2007

경계를 가지는 비점성 2유체 유동을 해석할 수 있는 수치해법을 개발하고 이를 이용하여 초기에 정지되어 있는 액체판의 끝단에서 일어나는 수축현상을 분석하였다. 경계면은 보오텍스 쉬트로 모델하였고 유동장은 와도격자법과 경계면추적법을 적용하여 계산하였다. 액체판의 끝단은 표면장력에 의해 수축되고 뭉툭한 형상을 취하게 되고, 이러한 끝단은 잘룩한 형상의 통로에 의하여 액체판에 연결되어 안쪽으로 끌려들게 된다. 이러한 현상을 비점성 조건에서 운동에너지 변화를 포함한 무차원 수의 함수로 분석하였다. 끝단의 수축속도는 로 파악되었고 표면장력파의 전파특성이 엄밀하게 조사되어야 함을 밝혔다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.687-690
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• 2002

Multimode boundary-layer transition on a NACA0012 airfoil is experimentally investigated under periodically passing wakes and the moderate level of free-stream turbulence. The periodic wakes are generated by rotating circular cylinders clockwise or counterclockwise around the airfoil. The free-stream turbulence is produced by a grid upstream of the rotating cylinder, and its intensity(Tu) at the leading edge of the airfoil is $0.5\;or\;3.5\;{\%}$. The Reynolds number ($Re_c$) based on chord length (C) of the alrfoil is $2.0{\times}10^5$, and Strouhal number ($St_c$) of the passing wake is about 0.7. Time- and phase-averaged streamwise mean velocities and turbulence fluctuations are measured with a single hot-wire probe, and especially, the corresponding wall skin friction is evaluated using a computational Preston tube method. The wake-passing orientation changes pressure distribution on the airfoil in a different manner irrespective of the free-stream turbulence. Regardless of free-stream turbulence level, turbulent patches for the receding wakes propagate more rapidly than those for the approaching wake because adverse pressure gradient becomes larger. The patch under the high free-stream turbulence ($Tu=3.5{\%}$) grows more greatly in laminar-like regions compared with that under the low background turbulence ($Tu=0.5{\%}$) in laminar regions. The former, however, does not greatly change the original turbulence level in the very near-wall region while the latter does it. At further downstream, the former interacts vigorously with high environmental turbulence inside the pre-existing transitional boundary layer and gradually lose his identification, whereas the latter keep growing in the laminar boundary layer. The calmed region is more clearly observed under the lower free-stream turbulence level and for the receding wakes. The calmed region delays the breakdown further downstream and stabilizes more the boundary layer.

• 대한기계학회논문집B
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• 제30권9호
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• pp.921-928
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• 2006

Wake-induced boundary-layer transition on a NACA0012 airfoil with zero angle of attack is experimentally investigated in periodically passing wakes under the moderate level of free-stream turbulence. The periodic wakes are generated by rotating circular cylinders clockwise or counterclockwise around the airfoil. The free-stream turbulence is produced by a grid upstream of the rotating cylinder, and its intensities $(Tu_{\infty})$ at the leading edge of the airfoil are 0.5 and 3.5%, respectively. The Reynolds number (Rec) based on chord length (C) of the airfoil is $2.0{\times}10^5$, and Strouhal number (Stc) of the passing wake is about 1.4. Time- and phase-averaged streamwise mean velocities and turbulence fluctuations are measured with a single hot-wire probe, and especially, the corresponding wall skin friction is evaluated using a computational Preston tube method. The patch under the high free-stream turbulence $(Tu_{\infty}=3.5%)$ grows more greatly in laminar-like regions compared with that under the low turbulence $(Tu_{\infty}=0.5%)$ in laminar regions. The former, however, does not greatly change the turbulence level in very near-wall region while the latter does it. At further downstream, the former interacts vigorously with high environmental turbulence inside the pre-existing transitional boundary layer and gradually loses its identification, whereas the latter keeps growing in the laminar boundary layer. The calmed region is more clearly observed under the lower free-stream turbulence level and with the receding wakes.