Background oriented stereoscopic schlieren (BOSS) for full-scale helicopter vortex characterization

Abstract

In this paper we present the application of a novel schlieren technique for two different helicopter tests. The optical method is referred to as “Background Oriented Schlieren” (BOS) in the following. Additionally the differences between BOS and an extension of it, the reference-free stereoscopic arrangement (BOSS in the following), will be discussed. Experimental studies have been carried out to investigate details of the vortex generation next to the blade tips of two different helicopters, an Eurocopter BK117 and an Sikorsky UH60. The background oriented techniques seem to well complete other optical techniques like shadowgraphy or focussing schlieren methods and yield additional quantitative information. Furthermore, they allow - in contrast to laser based techniques - to study the Reynolds-number depending vortex development in full-scale flight tests more easily.