1School of Aeronautics, Universidad Politécnica, 28040 Madrid, SpainCentre for Turbulent Research, Stanford University, Stanford, CA 94305, USA
2School of Aeronautics, Universidad Politécnica, 28040 Madrid, Spain
Tóm tắt
Numerical experiments on modified turbulent channels at moderate Reynolds numbers
are used to differentiate between several possible regeneration cycles for the
turbulent fluctuations in wall-bounded flows. It is shown that a cycle exists which is
local to the near-wall region and does not depend on the outer flow. It involves the
formation of velocity streaks from the advection of the mean profile by streamwise
vortices, and the generation of the vortices from the instability of the streaks. Interrupting
any of those processes leads to laminarization. The presence of the wall
seems to be only necessary to maintain the mean shear. The generation of secondary
vorticity at the wall is shown to be of little importance in turbulence generation
under natural circumstances. Inhibiting its production increases turbulence intensity
and drag.
