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SUMMARY:Nonlinear transitional mechanisms in boundary layers: a frequency 
 domain approach - Georgios Rigas (Imperial College London)
DTSTART:20220328T130000Z
DTEND:20220328T133000Z
UID:TALK171125@talks.cam.ac.uk
DESCRIPTION:By analog with the linear approaches\, and specifically the fr
 equency-response analysis\, we model transition from laminar to turbulent 
 flow as a stationary process where disturbances are continually supplied t
 o the system from the environment\, i.e. we consider the nonlinear recepti
 vity problem in the frequency domain. In order to calculate finite-amplitu
 de perturbations in the frequency domain\, we seek self-consistent solutio
 ns of the Navier-Stokes equations under the form of an expansion consistin
 g of a mean-flow solution\, a fundamental mode and N harmonics of the fund
 amental. We call the resulting equations Harmonic-Balanced Navier-Stokes (
 HBNS). Subsequently\, optimal nonlinear forcing mechanisms that lead to tu
 rbulence and maximise the skin-friction coefficient (drag) are calculated 
 using a variational method and direct-adjoint looping. The proposed nonlin
 ear input/output analysis method reveals the most dangerous nonlinear mech
 anisms that lead to turbulent dynamics in the frequency domain\, which can
  be viewed as the minimal forcing seed in the frequency domain.&nbsp\;
LOCATION:Seminar Room 1\, Newton Institute
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