Low-speed streaks instability in near wall turbulence with adverse pressure gradient

type de publication      communication internationale avec actes publiés
date de publication 2011
auteur(s) Ehrenstein Uwe; Marquillie Matthieu; Laval Jean-Philippe
numéro de papier 032027
  
conférence 13th European Turbulence Conference (ETC13)
     dates de 12-09-2011 à 15-09-2011
     lieu Warsaw, Poland
     nom des actes Journal of Physics. : Conference Series Vol. 318 (2011)
  
pages 1 – 8
résumé A direct numerical simulation of a turbulent channel flow with a lower curved wall is performed at Reynolds number Reτ ≈ 600. Low-speed streak structures are extracted from the turbulent flow field and base flows formed with conditional streaks averages, superimposing the mean streamwise velocity profile, are used for linear stability analyses. The instability in the presence of a strong pressure gradient at the lower wall is shown to be of varicose type, whereas at the upper wall (with weak pressure gradient) varicose and sinuous unstable modes can coexist. The onset of the dominant instability mechanism of varicose type is shown to coincide with the strong production peaks of turbulent kinetic energy near the maximum of pressure gradient on both the curved and the flat walls. The size and shape of the counter-rotating streamwise vortices associated with the instability modes are shown to be reminiscent of the coherent vortices emerging from the streak skeletons in the direct numerical simulation.
mots clés Hydrodynamic stability, Coherent structures, Flow phenomena in quasi-one-dimensional systems, Direct numerical simulations, Channel flow
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