Micro laval nozzle has been widely used in such areas as micro propulsion system, supersonic air-jet pulverization,laser cutting,etc.The gas flow characteristics for micro nozzles with different section shapes and different divergent section lengths were analyzed with the aid of computational fluid dynamics(CFD) simulation technology, which helped to determine the rules of nozzle type selection and the optimum divergent section length. The simulation results indicated that the exit velocity of two-dimensional axisymmetric nozzle is larger than that of rectangular section one, which shows that the two-dimensional axisymmetric type is recommended when the nozzle is in millimeter level. The flow fields of the two-dimensional axisymmetric nozzles with different divergent section lengths were investigated through the comparison of their exit velocities, thrust forces and efficiencies, which presents that the optimal divergent length is 3 mm in this research. The proposed simulation method can be applied to the selection of other nozzle parameters and the optimization of length determination, which can help to reduce the difficulty of manufacturability of micro-nozzle with excellent performance.
