1. 제 목 : A Linear Process in Nonlinear Flows


2. 연 사 : Professor John Kim


Department of Mechanical and Aerospace Engineering


University of California, Los Angeles


3. 일 시 : 1999년 9월 20일 (월) 17:00 - 18:00


4. 장 소 : 301동 1512호


5. 내 용 :


The transient growth due to non-normality of the eigenmodes of the linearized Navier-Stokes equations has received much attention during the past several years. It has been shown that certain disturbances can grow to in time proportional to . It has been postulated that this transient growth, which is a linear process, can lead to transition to turbulence at a Reynolds number smaller than the critical Reynolds number, below which a classical linear stability theory based on the modal analysis predicts that all small disturbances decay asymptotically. As such, some investigators attributed this linear process as a possible cause for subcritical transition in some wall-bounded shear flows. Some investigators further postulated that the same linear process is also responsible for the observed wall-layer streaky structures in turbulent boundary layers. The notion that commonly observed wall-layer structures are related to a linear process suggests that the same linear process may play an important role in fully nonlinear turbulent boundary layers. The role of this linear process in fully nonlinear turbulent flows is investigated. It is shown that the linear coupling term, which enhances non-normality of the linearized Navier-Stokes system, plays an important role in fully turbulent and hence, nonlinear flows. Near-wall turbulence is shown to decay without the linear coupling term. Other implications associated with the linear process will be discussed.


6. 문 의 : 최해천 교수 (☏ 880-8361)