Application of particle image velocimetry under cryogenic conditions

Cryogenic investigations of the trailing vortices of large future transport aircrafts have been performed on an aircraft half-model with different wing tip devices. The model has been installed in the cryogenic wind tunnel (KKK) of the German-Dutch wind tunnels (DNW) in Cologne. During the tests, PIV flow field measurements have been performed in addition to conventional force, moment, and pressure distribution measurements. The measurements of the velocity field gave an insight into important aerodynamic effects as, for example, the dependents of vortex strength with changing angles of incidence as well as the differences in the spatial vorticity distribution in the wake. The PIV technique offers special advantages for the investigation of those wakes at very low temperatures, but also yields to special experimental difficulties, which are also described in this article.