Widerstandsreduktion durch laminare Strömungskontrolle: Direkte und bionische Verfahren

Abstract

A body in a fluid flow is subjected to friction drag. Reducing this drag is desirable in many applications. One possibility of achieving a low friction drag is keeping the body’s boundary-layer laminar for a bigger part of the surface. This is not only possible through the shaping of the body, but also through active flow control. For some applications, active laminarisation of a flow can be achieved by the damping of Tollmien-Schlichting (TS) waves, unstable disturbances in the flow which are the main route for the transition to turbulence. For this, a counter-wave needs to be generated, which dampens the TS wave by negative superposition. This will be referred to as the ”direct method”. A different mechanism for the damping of TS waves is the use of compliant surfaces. The interaction of fluid and surface can dampen the waves. This method is inspired by a role model form nature the dolphin. However, as the dolphin utilizes multiple methods of drag reduction, it is unclear how big a difference its compliant skin makes. During the course of this work, different methods were used to directly dampen TS waves. Additionally, a method for the control of an actively displaceable wall segment was designed. This allows the testing of different wall compliances in experiments without having to modify the test setup’s hardware. The wall segment was driven by different actuator configurations, including configurations for the damping of oblique TS waves.