Particle Image Velocimetry for In-Flight Application - Preparation, Test and Lessons Learned -

Applying advanced non-intrusive flow visualization techniques to an in-flight environment is a challenging task which can provide invaluable data. The ability to capture complex flow structures under free atmospherical influences and in real flight conditions can potentially supply data for numerical technique validation and wind tunnel measurements. This paper will report on the installation of a modified PIV setup inside a DLR research aircraft and the subsequent PIV flight tests. During the project several problems occurred. On the one hand, a number of certification procedures were required and on the other hand, finding feasible tracer particles (i.e. seeding) presents a significant challenge as the use of standard PIV seeding generators in-flight is not a practical option. Therefore, another approach has to be pursued and this research has shown the best way to provide viable seeding is by flying through natural aerosols – such as those in clouds. The flight test campaign was been conducted in September 2009 at the German airport Braunschweig-Wolfsburg. During three flights with the Dornier Do228-101 aircraft, several flap settings, velocities, cloud layers and altitudes were flown and recorded by the implemented imaging and acquisition system. The captured flow structure is mainly driven by the propeller slipstream, the fuselage boundary layer, the flap downwash and the engine exhaust gas flow. Hence, no distinct flow pattern could be identified. In addition, the relatively small field of view also restricted the resolution of the flow information. The feasibility study presented here from an airborne in-flight PIV system has proven the applicability of this optical flow visualization tool. However, a number of significant challenges for the application of in-flight PIV still remain related to the aircraft operation and certification. Hence, future developments and improvements of this in-flight technique will be discussed in the full paper and the presentation for the symposium