Background Oriented Schlieren (BOS) measurement in supersonic flow with 4K high-speed camera

The Background Oriented Schlieren (BOS) technique is one of the novel measurement techniques and its application range is very wide. The principle of BOS is similar to that of the conventional schlieren technique, it exploits the bending of light caused by a refractive-index change corresponding to the density change in the medium. The BOS technique allows the quantitative measurement of density with a very simple experimental setup and proper image analysis. Only a background and a digital camera are required for the experiment, so that even full-scale experiments can be realized. In recent years, the development of the high-speed camera is remarkable and so many high-speed phenomena can now be captured. To realize the precise measurement with BOS technique using a high-speed camera, higher resolution (larger number of pixels) is desirable. In this paper, with technical support from Nobby Tech Ltd., a 4K high-speed camera (4096 x 2160 pixels) is applied to the BOS measurement of the lateral jet/cross flow interaction filed in the supersonic wind tunnel test as a trial of the quantitative density measurement with higher resolution. The measurement system consists of a 4K high-speed camera and a pulsed laser for background illumination. A telecentric optical system is also employed to improve the spatial resolution of the measurement. The measurement results of the BOS technique up to frame rates of 1000 fps with higher resolution are discussed.