Journal of Fluid Mechanics

The autonomous cycle of near-wall turbulence

a1 School of Aeronautics, Universidad Politécnica, 28040 Madrid, Spain
a2 Centre for Turbulent Research, Stanford University, Stanford, CA 94305, USA


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.

(Received May 19 1998)
(Revised January 26 1999)