Supersonic axisymmetric microjets: structure and laminar–turbulent transition

The supersonic core length of microjets and the influence of the laminar–turbulent transition on the core length are considered. Axisymmetric mini- and micronozzles with diameters from 341 to 10.4 μm are used. The microjet is studied with the use of a Pitot microtube, shadow flow visualization and hot-wire anemometry. It is demonstrated that the laminar–turbulent transition in the jet mixing layer exerts a dominating effect on the supersonic core length. The increasing of the supersonic core length is associated with the laminar flow in microjet. Decreasing of the supersonic core length is connected with the laminar–turbulent transition in microjet. Based on experimental results, a chart of microjet regimes is constructed. The influence of the Pitot tube diameter on the accuracy of supersonic core length determining is considered. The effect of the nozzle edge roughness on the supersonic core length is examined.