On the Size of the Eddies in the Outer Turbulent Wall Layer: Evidence from Velocity Spectra
The scaling of size of the momentum-bearing eddies in wall-parallel planes in the outer part of turbulent wall layers is analyzed, by examining spectra of the fluctuating velocities taken from direct numerical simulations and experiments. For all flows under scrutiny the normalized spectra highlight growth of the eddies size with the wall distance. The results indicate the capability of a modified mixing length (Pirozzoli, J Fluid Mech 702:521–532, 2012 ) of accounting with greater precision for the wall-normal variation of the size of the eddies bearing streamwise momentum. This observation can be explained by assuming that outer layer momentum streaks (superstructures) spread under the collective action of the other eddies, which impart a (nearly) uniform eddy diffusivity throughout the outer wall layer.
KeywordsWall-bounded flows Turbulence Coherent structures
I acknowledge that some results in this paper have been achieved using the PRACE Research Infrastructure resource JUGENE based at the Forschungszentrum Jülich (FZJ) in Jülich, Germany. Thanks are also due to Sean C.C. Bailey, Alexander J. Smits, Nicholas Hutchins, and Ivan Marusic, for providing experimental data and other useful information.
- 6.M. Bernardini, S. Pirozzoli, P. Orlandi, J. Fluid Mech. (2013). Under reviewGoogle Scholar