Three-dimensional measurements of density field on a supersonic microjet based on schlieren imaging

The high-speed three-dimensional(3D) quantitative schlieren technology based on fiber bundles is introduced. This technology uses a high-speed camera, two xenon lamps, a set of one-to-seven optical fiber bundles and a series of lenses to simultaneously collect schlieren images from seven different angles. Combining with the tomographic reconstruction, the 3D density distribution of the flow field can be obtained. This technology performs 3D dynamic measurements of supersonic microjet within a field of view of 43.37 mm × 43.37 mm × 43.37 mm at a frame rate of 2 kHz. The experimental results show the flow pattern downstream of the micro-nozzle outlet. Multiple reflected shock waves present a polyhedral shape throughout the micro-jet, and the jet diameter is the smallest at the shock unit. The length of the shock unit increases with the increasing of nozzle pressure ratio under different nozzle pressure ratios, and at the same pressure ratio, the length of the second shock unit reaches the maximum value.