BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:When turbulence first reaches the wall - Tamer Zaki (Johns Hopkins
  University)
DTSTART:20220328T133000Z
DTEND:20220328T140000Z
UID:TALK171128@talks.cam.ac.uk
DESCRIPTION:Laminar-to-turbulence transition in boundary layers is accompa
 nied by concentration of&nbsp\;the mean spanwise vorticity near and at the
  boundary.&nbsp\; The increase of wall vorticity\, or equivalently the wal
 l stress\, is even more pronounced in the instantaneous fields when a nasc
 ent patch of turbulence first reaches the wall.&nbsp\; The fluid dynamical
  mechanism for this increase is examined rigorously using the stochastic L
 agrangian formulation of the Navier-Stokes equations\, which quantifies al
 l&nbsp\;possible contributors.&nbsp\; We express the instantaneous wall vo
 rticity as the expectation of a stochastic Cauchy invariant in backward ti
 me\, with terms due the&nbsp\;(a) wall-vorticity flux (Lighthill source)&n
 bsp\;and (b) interior vorticity evolved by&nbsp\;nonlinear advection\, vis
 cous diffusion\, vortex&nbsp\;stretching&nbsp\;and tilting.&nbsp\; We eval
 uate these terms for an ensemble of transition events from a simulation of
  bypass transition that is publicly available through the&nbsp\;JHU databa
 se. &nbsp\;The results yield a&nbsp\;clear&nbsp\;picture of the origin of 
 the&nbsp\;enhanced wall vorticity in this flow\, which is not the Lighthil
 l source but instead a different mechanism suggested&nbsp\;by Lighthill (1
 963).\n&nbsp\;
LOCATION:Seminar Room 1\, Newton Institute
END:VEVENT
END:VCALENDAR