Density Measurements in an Axisymmetric Underexpanded Jet by Background-Oriented Schlieren Technique

The background-oriented schlieren (BOS) technique has been applied to obtain the mean density field of a complex underexpanded jet flow. The measurements were made on an axisymmetric sonic jet operating at ideally expanded and highly underexpanded values of nozzle pressure ratios. The methodology involved two steps: validation of the filtered backprojection tomography used here, by making measurements of a four-jet configuration followed by density measurements on axisymmetric sonic jets. Pitot measurements made on an ideally expanded sonic jet were utilized for validation of BOS. The presented density fields show that meaningful quantitative data can be extracted by using minimal hardware with this technology.