Home
학과소식
세미나
기존 세미나
기존 세미나
[기계] Prof. Philip Hall초청 세미나 개최
2009년 11월 6일 아래와 같이 Philip Hall 교수의 강연이 개최됩니다. 학생여러분의 많은 참여 바랍니다.
1. 제 목 : COHERENT STRUCTURES IN SHEAR FLOWS AND VORTEX WAVE INTERACTION THEORY
2. 연 사 : Professor Philip Hall
Director, Institute for Mathematical Sciences, Imperial College, London.
3. 일 시 : 2009. 11. 6.(금) 14:00
4. 장 소 : 301동 1512호
5. 내 용 : The equations governing turbulent flows are known, but they defy mathematical and numerical attacks because of their complexity and because the computer capacity required far exceeds that of existing computers. In recent years immense interest has been focused on so-called self-sustained processes in turbulent shear flows where the importance of waves interacting with streamwise vortex flows has been elucidated in a number of papers on the numerical solution of the Navier Stokes equations; see for example the work of Waleffe and colleagues, Kerswell, Gibson, etc. These processes appear to have a striking resemblance to coherent structures observed in turbulent shear flow and for that reason they are often referred to as exact coherent structures. It is shown that the structures associated with the so-called 'lower branch' state, which has been shown to play a crucial role in these self-sustained process, is nothing but a Rayleigh wave vortex interaction with a wave system generating streamwise vortices inside a critical layer. The theory enables the reduction of the 3D Navier Stokes equations to a coupled system for a steady streamwise vortex and a linear inviscid wave system. The reduced system for the streamwise vortices must be solved with jump conditions in the shear across the critical layer and the position of that layer constitutes a nonlinear pde eigenvalue problem. Remarkable agreement between the asymptotic theory and numerical simulations is found thereby demonstrating the importance of vortex-wave interaction theory in the mathematical description of coherent structures in turbulent shear flows. The theory offers the possibility of drag reduction in turbulent shear flows by controlling the flow to the neighborhood of the lower branch state. The relevance of the work to more general shear flows is also discussed.
6. 문 의 : 기계항공공학부 이우일 교수 (☏1657 )
1. 제 목 : COHERENT STRUCTURES IN SHEAR FLOWS AND VORTEX WAVE INTERACTION THEORY
2. 연 사 : Professor Philip Hall
Director, Institute for Mathematical Sciences, Imperial College, London.
3. 일 시 : 2009. 11. 6.(금) 14:00
4. 장 소 : 301동 1512호
5. 내 용 : The equations governing turbulent flows are known, but they defy mathematical and numerical attacks because of their complexity and because the computer capacity required far exceeds that of existing computers. In recent years immense interest has been focused on so-called self-sustained processes in turbulent shear flows where the importance of waves interacting with streamwise vortex flows has been elucidated in a number of papers on the numerical solution of the Navier Stokes equations; see for example the work of Waleffe and colleagues, Kerswell, Gibson, etc. These processes appear to have a striking resemblance to coherent structures observed in turbulent shear flow and for that reason they are often referred to as exact coherent structures. It is shown that the structures associated with the so-called 'lower branch' state, which has been shown to play a crucial role in these self-sustained process, is nothing but a Rayleigh wave vortex interaction with a wave system generating streamwise vortices inside a critical layer. The theory enables the reduction of the 3D Navier Stokes equations to a coupled system for a steady streamwise vortex and a linear inviscid wave system. The reduced system for the streamwise vortices must be solved with jump conditions in the shear across the critical layer and the position of that layer constitutes a nonlinear pde eigenvalue problem. Remarkable agreement between the asymptotic theory and numerical simulations is found thereby demonstrating the importance of vortex-wave interaction theory in the mathematical description of coherent structures in turbulent shear flows. The theory offers the possibility of drag reduction in turbulent shear flows by controlling the flow to the neighborhood of the lower branch state. The relevance of the work to more general shear flows is also discussed.
6. 문 의 : 기계항공공학부 이우일 교수 (☏1657 )