Material selection and manufacturing of riblets for drag reduction: An updated review

Riblets are a well-researched and understood passive method for achieving viscous drag reduction. Since the 1970s, researchers have found that, with riblets, viscous drag reduction in the order of 8% is achievable in turbulent air and fluid flows. Most of the relevant literature provides insight into the drag-reductive mechanisms of riblets and the effect of riblet morphological design in varying flow conditions. A few recent studies have begun to investigate the influence of material properties on the drag-reductive ability of riblet surfaces with promising results. We here provide an updated review of material selection and riblet manufacture and show current trends. A brief summary is provided of the theories of riblet drag-reductive ability, riblet surface design, the role of material selection for drag reduction and current manufacturing techniques.