SIMULATING TURBULENT-FLOW OVER THIN ELEMENT AND FLAT VALLEY V-SHAPED RIBLETS

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.