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DTSTAMP:20260424T140921Z
UID:65239ed63096e937576332@ist.ac.at
DTSTART:20240304T143000
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DESCRIPTION:Speaker: Hassan M. Nagib\nhosted by Bjorn Hof\nAbstract: Utiliz
 ing the three-pronged approach of experimental measurements\, computationa
 l results (DNS) and matched asymptotic analysis\, we have reexamined the t
 hree canonical wall-bounded turbulent flows of pipe\, channel and zero pre
 ssure gradient boundary layer. Detailed and systematic study confirmed the
  non- universality of the Krmn constant (k) reported in 2008 by Nagib & Ch
 auhan Variations of von Krmn coefficient in canonical flows\, PoF 20\, 101
 518. Recently\, a new matching approach also revealed an inner- outer over
 lap consisting of a superposition of log-law and a linear term\, as detail
 ed in paper by Monkewitz & Nagib The hunt for the Krmn constant Revisited\
 , JFM 967\, A15\, 2023. DOI: https://doi.org/10.1017/jfm.2023.448. A simil
 ar linear term was suggested by Afzal & Yajnik\, JFM (1973 & 1970) and Luc
 hini (2017) PRL 118\, 224501. In our results\, we find that the coefficien
 ts of both the log and linear terms are dependent on the pressure gradient
  of the flow. We utilized experimental data obtained under various favorab
 le and adverse pressure gradients in the NDF wind tunnel at IIT and the MT
 L wind tunnel at KTH\, to extract the parameters of the "Log-Linear" overl
 ap region in pressure gradient boundary layers.After many decades of exper
 ience with canonical wall-bounded turbulent flows\, we recognize fully dev
 eloped pipe flow as the ideal flow to compare computations and experiments
 . With collaborators at several universities\, we have conducted experimen
 ts\, with Ret up to 33\,000\, and DNS for pipe flow at Ret = 550 & 1\,000\
 , with several resolutions\, and extended Eddy Turnover Times (ETT) of up 
 to 200. New criteria for resolution and an existing criterion for converge
 nce of DNS are being developed and confirmed\, respectively. We find that 
 higher resolution DNS and longer computational times are required for wall
 -bounded turbulence\, compared to values commonly used. Finally\, the impa
 ct of the new combined log-law and linear term on Textbooks\, Lecture Note
 s\, RANS Codes and Turbulence Models will be highlighted.
LOCATION:Office Bldg West / Ground floor / Heinzel Seminar Room (I21.EG.101
 )\, ISTA
ORGANIZER:swiddman@ist.ac.at
SUMMARY:Hassan M. Nagib: Recent Developments in Overlap Region of Wall Boun
 ded Turbulence
URL:https://talks-calendar.ista.ac.at/events/4501
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