Turbulent boundary layer characteristics over streamwise grooves

Turbulent boundary layer characteristics over streamwise grooves (on the order of 15 wall units in height and spacing) have been quantified in a water channel using hot film anemometry. The turbulent structure over both smooth and riblet surfaces has been investigated using traditional cross correlations and triple correlations. The VITA technique has been used to detect and count turbulent bursts over both surfaces. A 30 percent reduction in the measured bursting frequency was found for the riblet surface. Local skin friction reductions were found towards the end of the riblet model; however, the total drag for both surfaces was the same. Flow visualizations show a quiescent slow moving viscous-like flow in the grooves of the riblet plate. All the measurements indicate a subtle change in the near wall flow, with the outer flow in the boundary layer remaining the same.