16. Development of Particle Image Velocimetry for In-Flight Flow Measurement

Wind tunnel testing is widely used for the development and testing of numerous aerodynamic systems. Mature laser based optical methods such as particle image velocimetry (PIV) also now offer detailed flow diagnostics in the wind tunnel environment. The majority of wind tunnels, however, cannot correctly scale both Reynolds and Mach number simultaneously. In-flight testing from a full scale aircraft offers the potential to take correctly scaled data to validate both wind tunnel and computational models. Furthermore, PIV has the potential to take detailed, non-intrusive velocity data from a full scale flight test. The following chapter reports on what the authors believe is the seminal application of a modified PIV setup inside a DLR Dornier DO 228-101 research aircraft and the subsequent PIV flight tests. These tests were completed as part of a major European Framework 6 research program called Advanced In-flight Measurements (AIM). In particular, the chapter reports on the major challenges that were overcome by the German Aerospace Center (DLR) together with Cranfield University to complete the flight tests. These challenges included the laser safety considerations for the test, the certification of the aircraft and the requirement for suitable seeding during the tests. The latter issue was overcome by flight testing inside a suitable cloud formation and successful PIV data was recorded over a series of three flight tests in a region adjacent to the outside of the cabin. The PIV images obtained yield high data quality inside the turbulent boundary layer.