The time-dependent flow over riblets of various shapes is calculated u
sing a control volume finite element simulation technique and assuming
a model of the near-wall viscous Bow region of a turbulent boundary l
ayer. The cross-sectional shapes considered include thin element blade
riblets and saw-toothed riblets (but with flat valleys), which are si
milar to the more common continuous V-shaped riblets. Turbulence stati
stics derived from the calculations include skewness and flatness fact
ors. It is concluded that to achieve maximum drag reduction, riblets n
ot only need to ensure a thicker than usual viscous laminar-like flow
in their grooves, but also the transient momentum exchange must be min
imized between this inner region and the larger-scale outer motions as
sociated with quasistreamwise vortices.