Flow over bio-inspired 3D herringbone wall riblets

Under the inspiration of small riblets of shark skin, the microgroove drag reduction riblets whose direction set along fluid flow have been widely investigated. Herringbone-type riblets of bird flight feather are seldom exploited although bird also has excellent flight performance. Inspired from the flight feather, novel bio-inspired plane-3D (p-3D) and spatial-3D (s-3D) herringbone wall riblets are proposed. Through experiment measurement of drag reduction in water tunnel, maximum drag reduction of p-3D and s-3D herringbone riblets was about 17 and 20 %, higher than traditional microgroove riblets. Moreover, significant change of drag reduction was also found by change of the angle between herringbone riblets. In particular, maximum drag reduction occurred as angle between herringbone riblets was about 60 degrees close to real flight feather, which indicates that microstructure of bird flight feather has great impact on flight performance.