Convergent-divergent (C-D) riblets (or herringbone riblets) are a new type of surface patterns which begins to receive research attention in the recent years. They consist of sections of left-tilted and right-tilted micro grooves which are joined together side by side (see figure). Such micro patterns have been found on shark skins and on the secondary flight feathers of birds. Due to the directional orientation of these micro grooves, C-D riblets are capable of generating weak large-scale secondary flow motion in the near-wall region resulting in a significant modification of boundary layer characteristics in the spanwise direction.
In this seminar, the finding from a series of experimental studies undertaken at Manchester demonstrating the effectiveness of this type of bio-inspired riblets in reducing the pressure losses in linear cascades and attenuating shockwave-induced flow separation will be presented. The results from both computational and experimental studies on flat-plate boundary layers and channel flows aiming to understand the impact of these riblets on boundary layer development and turbulent structures will also be shown.