Sonic point position and critical pressure ratio in micro nozzles

This research is aimed at improving the performance of micro-space propulsions and micro gas turbine generators. The gas flow characteristics in 2D convergent-divergent micro nozzle were analyzed by numerical simulation based on finite-volume method. The throat width of micro nozzle is 1-200 μm and the expansion area ratio is 1.7. The numerical results indicate that the outlet March number and critical pressure ratio decreases with the decreasing of the throat width. The numerical results also show that the first sonic point position moves away from the throat to the outlet of the micro nozzle with decrease of the throat width. These particular behaviors are attributed to the increased surface-to-volume ratio leads to high viscosity dissipation in the micro nozzle.