Investigations of helicopter rotor blade tip vortices in wind tunnels and in flight

The advancement of measurement systems and technology keeps pushing experimental aerodynamics, which is particularly apparent for the application of particle image velocimetry (PIV) and background oriented schlieren (BOS) techniques in helicopter aerodynamics. Unsteady and complex features of helicopter flows present a vast number of specific challenges to experimentalists, including transonic flow, concentrated vortices and dynamic stall. To illustrate the impact of the technological advancements on the way helicopter aerodynamics is studied today, some recent PIV applications will be described, using the examples of blade tip vortex investigations. The potential of combining PIV with complementary optical measurement techniques will be outlined considering large and full scale applications. Based on some recent trends, a glimpse into the future of PIV in helicopter aerodynamics will be ventured to complete the picture