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SUMMARY:The precessing vortex core instability in swirled jets - Santosh H
 emchandra\, Indian Institute of Science\, Bangalore
DTSTART:20221111T160000Z
DTEND:20221111T170000Z
UID:TALK182969@talks.cam.ac.uk
CONTACT:Prof. Jerome Neufeld
DESCRIPTION:Swirled jets are technologically important flows that have wid
 e ranging applications in gas turbine propulsion and power generation syst
 ems. Combustors in these devices use nozzles that impart swirl to the flow
  as it passes through. The intensity of swirl is quantified by the swirl n
 umber\, S\, which is the ratio of the streamwise fluxes of azimuthal and s
 treamwise flow momentum. Sufficiently high values of S cause the axial vor
 tex in the flow to break down and create an axi-symmetric recirculation zo
 ne in the flow - commonly referred to as the ‘vortex breakdown bubble’
  (VBB). The precessing vortex core (PVC)\, is a self-excited instability i
 n this type of flow that occurs due to the precession of the VBB\, resulti
 ng in a helical rollup of the surrounding shear layer. \n\nI will present 
 results from a weakly non-linear asymptotic analysis of a swirled axi-symm
 etric jet at a Reynolds number\, Re=59\,000. This jet has been the subject
  of several studies in Jacqueline O’Connor’s group at Penn. State. The
  results show that the onset of vortex breakdown at a critical swirl numbe
 r\, S_c=0.61 results in the emergence of a linearly marginally unstable hy
 drodynamic mode that induces VBB precession. This in turn\, results in the
  emergence of a stable limit-cycle flow oscillation\, as verified by the c
 oefficients in the Stuart-Landau equation governing the oscillation amplit
 ude. \n\nThe PVC limit cycle oscillation arises due to intrinsic flow feed
 back at the leading edge of the vortex breakdown bubble. More recent exper
 iments performed in collaboration with other groups have shown that introd
 ucing a centrebody upstream of the breakdown bubble\, does result in the s
 tabilization of the PVC. This provides further evidence that supports conc
 lusions of our non-linear asymptotic theory for the PVC.
LOCATION:MR2\, Centre for Mathematical Sciences\, Wilberforce Road\, Cambr
 idge
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