Free flight boundary layer investigations by means of Particle Image Velocimetry

Abstract

A comprehensive flight test study involving an advanced flow field measurement technique, a particle sizing system as well as a conventional single‐point measurement system is herewith presented. The main objective of this campaign was the assessment of the accuracy and performance of Particle Image Velocimetry under flight test conditions. Hence, a PIV system was arranged inside a DLR research aircraft to determine the boundary layer flow close to the fuselage surface. In addition, a traversable rake with two differential pressure probes was installed close to the field of view of the two stereoscopic PIV cameras to measure the velocity in a conventional and reliable way. The seeding source for the PIV system were naturally occurring hydrometeors like cloud droplets, haze or precipitation. The behaviour of these tracer particles with varying diameters inside the examined boundary layer is to a certain extend unknown. Hence, a particle sizing system based on the Interferometric Laser Imaging for Droplet Sizing (ILIDS) technique was also introduced, designed and certified to allow a derivation of the particle dynamics during the PIV measurements.