Density field measurements of axisymmetric underexpanded microjets by rainbow schlieren deflectometry

The rainbow schlieren deflectometry is applied for a supersonic microjet where an axisymmetric convergent nozzle with a diameter of 1 mm at the nozzle exit is used as a test nozzle. Flow visualization of microjets is performed at a nozzle pressure ratio of 4.0 to produce an underexpanded sonic jet. The density field of the microjet is reconstructed by the Abel inversion method based on the assumption of axisymmetric flows. Furthermore, comparisons of the rainbow schlieren deflectometry with the MachZehnder interferometry for the magnitude of the density gradient vector on the cross-section including the jet centerline are conducted to examine effects of the measuring techniques on the flow topology.