BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Genesis of coherent structures through an interactive bypass trans
 ition process - Tardu\, S (LEGI)
DTSTART:20080909T145000Z
DTEND:20080909T151000Z
UID:TALK13352@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:The interaction between two localized disturbances is analyzed
  in a subcritical channel flow through direct numerical simulations. The i
 nitial perturbations are in the form of two pairs of counter rotating vort
 ices. One of them interacts with the wall normal vorticity layers set-up n
 ear the wall\, by compressing or stretching locally part of them through t
 he straining motion it induces. The breakdown of spanwise symmetry leads t
 o the rapid development of a new wall normal vorticity patch that is tilte
 d by the shear and rolls up into a new small-scale streamwise vortex. The 
 process results in a localized turbulent spot at later stages of developme
 nt. A detailed analysis is carried out to determine the role of different 
 parameters entering in the physics of the mechanism. Several critical thre
 sholds that trigger the interactive bypass transition process are found an
 d analyzed. The similitude parameters resulting from the parametric invest
 igation coincide well with those governing the self-sustaining Reynolds sh
 ear stress producing eddies in the buffer layer of a fully developed turbu
 lent wall flow. It is suggested that the mechanism we propose may play som
 e role in the regeneration cycle of the near wall turbulence generating st
 ructures by precisely bypassing the three-dimensional streak instability m
 echanism. An active strategy based on this process is applied to the mixin
 g in microsystems. The specific interactions asymmetrically distributed in
  space lead to a better mixing locally in time and space leading to the po
 ssibility of active control of scalar transport in micro devices. 
LOCATION:Seminar Room 1\, Newton Institute
END:VEVENT
END:VCALENDAR