In-flight flow visualisation using Particle Image Velocimetry

Abstract

Applying advanced non-intrusive flow visualisation 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. Within the scope of a European research project several optical methods have been implemented to different types of aircraft to test their feasibility during flight or ground based vortex investigations. This paper reports 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. PIV laser systems in general are hazardous in their operation and high safety standards have to be defined to tackle the severe risk of such a high energy light source. These provisions resulted in operational restrictions during the flights. The arrangement of this experimental procedure was specified and certified for a Dornier DO 228-101 aircraft by the German Aerospace Center (DLR) together with Cranfield University. Furthermore, 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.