Study of axisymmetric underexpanded microjets by rainbow schlieren methods

The rainbow schlieren deflectometry is applied for an underexpanded microjet issued from an axisymmetric convergent nozzle with a diameter of 1 mm at the nozzle exit. The nozzle pressure ratio is held constant at 4.0 to produce weak shocks in the jet plume and the Reynolds number based upon the diameter as well as flow properties at the nozzle exit is 5.91×104. The density field of the microjet is reconstructed using the Abel inversion method with the assumption of axisymmetric free jets. The flow feature on cross-section including the central axis of the microjet is demonstrated using various visual representations such as the vertical knife-edge schlieren, the horizontal knife-edge schlieren, the bright-field schlieren and shadowgraphy.