- Particle Image Velocimetry - Development and Certification of a Promising Tool for In-Flight Flow Flied Measurements

Nowadays, advanced optical measurement methods for wind tunnel or laboratory applications become more and more sophisticated and relatively easy to employ, even in complex and severe experimental environments. Hence, the European research project AIM (Advanced In-flight Measurement Techniques) intended to transfer the present experiences of optical deformation and flow visualisation tools to flight tests in order to measure at real aircraft and flight Reynolds numbers. Within three flight tests conducted in September 2009, PIV (Particle Image Velocimetry) recordings have been acquired with the help of a commonly used and well approved PIV system. A highly turbulent and intermittent flow field was recorded which was mainly influenced by the propeller slipstream, the fuselage boundary layer and the flap downwash. The outcome of this campaign proved the applicability of this optical flow measurement tool for flight testing. In this regard, the main advantages of the PIV technique are its non-intrusive nature as well as the capability of providing velocity information with high spatial resolution in a flow field. This ability ensures the determination of valuable instantaneous velocity vector field data during flight tests, whereas on the other side external probes or intrusive sensors could only obtain discrete single point values of the desired parameters. Nevertheless, a number of significant challenges for the application of in-flight PIV to future flight tests still remain related to the aircraft operation and certification. This paper presents and discusses the preparation, realisation and results of the in-flight PIV measurement campaign as well as future developments and improvements which have to be pursuit in order to make PIV a cost efficient flight test technique