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SUMMARY:3D Self-Sustaining Processes in Shear Flows with and without Surfa
 ce Waves - Greg Chini (University of New Hampshire)
DTSTART:20151019T120000Z
DTEND:20151019T130000Z
UID:TALK61536@talks.cam.ac.uk
CONTACT:Doris Allen
DESCRIPTION:Surface waves modify the fluid dynamics of the upper ocean not
  only through wave breaking but also through phase-averaged effects involv
 ing the surface-wave Stokes drift velocity.  Chief among these rectified e
 ffects is the generation of a convective flow known as Langmuir circulatio
 n (or ``Langmuir turbulence").  Like stress-driven turbulence in the absen
 ce of surface waves\, Langmuir turbulence is characterized by streamwise-o
 riented quasi-coherent roll vortices and streamwise streaks associated wit
 h spanwise variations in the streamwise flow.  To elucidate the fundamenta
 l differences between wave-free (shear) and wave-catalyzed (Langmuir) turb
 ulence\, two separate asymptotic theories are developed in parallel.  Firs
 t\, a large Reynolds number analysis of the Navier--Stokes equations that 
 describes a self-sustaining process (SSP) operative in linearly stable wal
 l-bounded shear flows is recounted.  This theory is contrasted with that e
 merging from an asymptotic reduction in the strong wave-forcing limit of t
 he Craik--Leibovich (CL) equations governing Langmuir turbulence.  The com
 parative analysis reveals important structural and dynamical differences b
 etween the SSPs in shear flows with and without surface waves and lends fu
 rther support to the view that Langmuir turbulence in the upper ocean is a
  distinct turbulence regime.\n\n
LOCATION:MR5\, Centre for Mathematical Sciences
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