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TZID:Europe/Vienna
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DTSTART:20180325T030000
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DTSTART:20181028T020000
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DTSTAMP:20260404T065947Z
UID:5af99e7ce7000493801177@ist.ac.at
DTSTART:20180517T133000
DTEND:20180517T150000
DESCRIPTION:Speaker: Elena Marensi\nhosted by Björn Hof\nAbstract: Recent 
 experimental observations (Khnen et al. 2018) show that a flattened stream
 wise velocity profile destabilises turbulence. By constructing variational
  problems that seek the minimal seed for turbulence\, we show that flatten
 ing of the mean streamwise velocity profile also enhances stability of the
  laminar base flow\, thus potentially preventing the transition to turbule
 nce. To mimic the presence of a baffle that locally flattens the base prof
 ile\, we apply a localised force. In order to generate initial conditions 
 that may be considered to model ambient disturbances\, we first compare th
 e (unforced) transition behaviour of the minimal seed with several forms o
 f randomised initial disturbances in the range Re=2400 to 10000. Scalings 
 Ec? Re?? are obtained with ? in the range 2 ? 3 for different forms of dis
 turbance\, with ? ? 2.8 for the minimal seed. We find that the energy of t
 he minimal seed after the Orr and oblique phases is close to that of the l
 ocalised random disturbance\, so that in this sense the minimal seed after
  the oblique phase is a reasonable proxy for measuring transition threshol
 ds. Feeding simulations in the presence of localised forcing with the init
 ial conditions generated above\, we continue to find increases in Ec \, i.
 e. enhanced stability of the laminar flow\, and destabilisation of turbule
 nce. Drag reduction is found even when the turbulence is not fully relamin
 arised by the forcing.
LOCATION:Foyer seminar room Ground floor / Office Bldg West (I21.EG.128)\, 
 ISTA
ORGANIZER:sdanzing@ist.ac.at
SUMMARY:Elena Marensi: Stabilization of pipe flows by a flattened mean prof
 ile
URL:https://talks-calendar.ista.ac.at/events/1247
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