Experimental arrangement for particle image velocimetry on the main rotor of a helicopter
Measured vorticity of a blade Tipp vortex
In the department of helicopters the tip vortices are investigated mainly using experimental methods. In addition to experiments on a scale rotor testbed in a laboratory environment, experiments on a fully-equipped helicopter model in a wind tunnel provide insights into the formation and propagation of the tip vortices. The experimental investigations are performed in close cooperation with the Institute of Flight Systems and are included in the DLR project ACTOR and the international projects GOAHEAD, HART2 and STAR. In addition, the blade tip vortices are being investigated in flight tests on the DLR’s BO105 flight test helicopter in the European project AIM. The aim of these investigations is an understanding of the flow phenomena at the formation, ageing and interaction of the tip vortices. The development of the tip vortex in the nearfield wake of the rotor blade is of particular interest, since this region feeds back to the blade tip and allows new insights into the optimisation of the blade for aerodynamic or aeroacoustic performance.
The investigation of the vortices uses non-invasive optical methods, of which the most important are Particle Image Velocimetry (PIV) for the measurement of the velocity field, Background Oriented Schlieren (BOS) for the measurement of the density field, and Speckle Pattern Recognition (SPR) for an instantaneous measurement of the blade geometry under load. The different methods are combined and synchronised so that a time-accurate analysis of the formation and evolution of the tip vortex is possible for either an isolated blade or for a real helicopter.
The research on the rotor tip vortex is performed in cooperation with national and international partners. This includes a long-term and close cooperation with the German-French research institute Saint Louis (ISL) and a transatlantic cooperation with the NASA and the US-Army.