Learning from dolphin skin - Active transition delay by distributed surface actuation

Abstract

The goal of this project was the development of an active laminarisation method in order to reduce skin friction drag. Laminar-turbulent boundary layer transition on unswept two-dimensional wings is mainly caused by Tollmien-Schlichting (TS-) waves. Based on an actively driven compliant wall as part of the wing's surface, a method for attenuation of these convective instabilities was developed. Different arrangements of piezo-membrane actuators were investigated with an array of highly sensitive surface flow sensors and appropriate control strategies. Spanwise differentiated and streamwise cascaded actuation were used as well as inclined wall displacement. The onset of transition could be shifted downstream by 100mm or six average TS-wave lengths. Additionally, the investigation of the boundary layer flow downstream of the active wall area and an efficiency estimation are presented in this contribution. © 2012 Springer Berlin Heidelberg.