Laminar and turbulent flow over optimal riblets

In the search for viscous drag reduction, many different techniques have been developed and investigated. One of the more interesting techniques is the drag reduction method involving the use of `riblets'. Riblets are micro-grooves on the bounding surface that are aligned with the mean flow direction; this method is particularly attractive due to its completely passive nature. Riblets have been thoroughly investigated in recent years. A considerable amount of experimental data has been collected regarding the flow over various shapes, sizes, and spacings of riblets in the turbulent regime. It has been found that drag reduction on the order of 8% can be achieved for flow over a flat plate mounted with riblets, if the proper spacings and heights are used. The purpose of the present work is twofold: First, to investigate optimal shapes of riblets, and second to compare our detailed numerical results for triangular riblets with recenly obtained experimental results.