Advanced flow velocity field metrology and their application to helicopter aerodynamics

Abstract

Particle image velocimetry (PIV) is increasingly used to investigate unsteady velocity fields instantaneously. PIV allows the recording of a complete velocity field in a plane of the flow within a few microseconds. It thereby provides information about unsteady flow fields which is difficult to obtain with other experimental techniques. The short acquisition times and fast availability of data reduce the operational time and hence cost in large-scale wind tunnels and test facilities. This is especially interesting for investigations related to noise emission of helicopters, which become more and more important, and for studies related to adapive blade profiles. The induced velocities of the blade tip vorticies, the vortex strenght, and miss-distance relative to the advancing rotor blades are object of many wind tunnel investigations. Measurements of local flow vectors at positions close to the rotor blade tips were performed in the Large Low-speed wind tunnel Facility (LLF) of the German-Dutch Wind tunnel (DNW). Aditionally, measurements on pitching airfoils including adaptive techniques are presented and discussed. These tests were conducted in DNW's transonic wind tunnel (TWG) in Göttingen