Unsteady Background Oriented Schlieren Measurements at Industry Scales

Measurement of jet flows and their associated acoustic emission fields is an important area of study and can have profound impacts on fast jet design and performance. Methods of investigating such flows in industrial facilities are often hampered by poor optical access, rendering some conventional approaches such as schlieren imaging impossible. This study demonstrates high-speed, unsteady, background oriented schlieren (BOS) measurements of supersonic jets, applicable to industrial facilities. BOS experiments are conducted at representative distances and physical scales to those that would be experienced in an industrial transonic wind tunnel. Comparisons with traditional mirror-based schlieren are made, for jets run at three representative pressure ratios (overexpanded, ideally expanded, and underexpanded), demonstrating the comparative clarity of the two methods. BOS has been shown to be capable of resolving the primary flow structures and acoustic fields for high-speed jets, comparable with traditional mirror-based schlieren system results, with a more compact experimental setup, hence suitable for implementations in industrial transonic wind tunnels.