L. Djenidi et Ra. Antonia, LASER-DOPPLER ANEMOMETER MEASUREMENTS OF TURBULENT BOUNDARY-LAYER OVER A RIBLET SURFACE, AIAA journal, 34(5), 1996, pp. 1007-1012
Laser Doppler anemometer measurements in a turbulent boundary layer do
wnstream of a change from a smooth wall to a V-grooved riblet surface
provide some insight into the way the near-wall turbulence structure a
djusts to the new boundary condition. Depending on the riblet dimensio
ns, this adjustment results either in drag reduction or drag increase,
In the former case (s(+) less than or similar to 25, where s is the d
istance between neighboring riblet tips and + denotes normalization by
wall variables), the turbulence structure is essentially similar to t
hat on a smooth wall. There are major structural differences in the la
tter case (s(+) greater than or equal to 25). Although near-mall secon
dary motions occur in both cases, the motions are much weaker when the
riblets act to reduce the drag.