Supersonic micro-jet of straight micro-tube exit

The experimental investigations on the phenomenon of supersonic flow at the exit of straight micro-tubes with diameters ranging from 150 to 530 mu m were conducted. The successive incident and reflected shock wave on supersonic and under-expanded flow were visualized by the Shadowgraph and Schlieren methods. The pressure and Mach number of the under-expanded supersonic flow were determined by the angle of the shock wave generated from the needle tip. It was found that the Mach number at the exit of straight micro-tubes is beyond unity because shock waves are generated from the needle tip at the micro-tube exit. Additionally, numerical simulations based on ALE (Arbitrary-Lagrangian-Eulerian) were performed with the same conditions as the experiments to validate their results. The LB1 turbulence model was used for the turbulent flow. The compressible momentum and energy equations with the assumption of ideal gas were solved. The computational domain extends to the downstream region. The two results are in excellent agreement. The Mach number at the exit ranges from 1.16 to 1.27. The flow characteristics of the under-expanded supersonic gas flow in a straight micro-tube were revealed.