Flexibility and versatility enhancements due to a portable optical system for the Background-Oriented Schlieren techniques

We propose a Portable image Fibre Background-Oriented Schlieren (Portable Fibre BOS) technique that has a compact flexible optical system consisting of a commercial camera lens, a commercial optical image fibre, and a camera with a camera lens. The Portable Fibre BOS techniques would lead to high versatility as well as cost-effectiveness for time-resolved three-dimensional density measurements in supersonic wind tunnel facilities. This is because a commercial compact optical system is relatively easily arranged around the test section compared with a conventional time-resolved three-dimensional measurement system which several cameras are positioned around a test section in a wind tunnel facility. The Fibre BOS including its portable mode presented in this study achieves a time-resolved three-dimensional measurement using a single high-speed camera. In this study, we investigated the characteristics of the Portable Fibre BOS, especially the relationship between an image fibre and the commercial camera lens for the field of view and a spatial resolution. The experimental and analytical results show that the spatial resolution and the field of view depend significantly on an image fibre diameter and the size of a fibre core. A large fibre diameter and a small core size lead to a good spatial resolution.