基于CFD的微型拉伐尔喷嘴选型与扩张段长度仿真优化研究

毫米级微型拉伐尔喷嘴应用于微推进系统、超音速气流粉碎技术、激光切割等领域。确定微喷嘴基本参数后，根据可加工性要求，喷嘴选型和喷嘴扩张段长度直接影响到加工工艺难度，利用计算流体力学（computational fluid dynamics以下简称CFD）分析方法，对不同类型和不同扩张段长度的喷嘴进行流场仿真，确立了本研究微喷嘴的选型规则和最优扩张段长度。结果表明：二维轴对称喷嘴相比矩形截面喷嘴具有较大的出口速度，建议毫米级喷嘴选型时采用二维轴对称喷嘴；对不同扩张段长度的二维轴对称喷嘴的流场仿真分析，通过对比喷嘴出口中心速度、推力及效率，表明在本研究条件下扩张段长为3mm时是最优长度。CFD仿真分析方法可用于其它微型拉伐尔喷嘴的选型及扩张段长度的确定,研究有助于在保证喷嘴性能的前提下，降低喷嘴加工难度。

Numerical Calculation of a Millmetre-sized Laval Nozzle and Optimization of the Length of Divergent Section Based on CFD

Micro laval nozzle has been widely used in such areas as micro propulsion system, supersonic air-jet pulverization, laser cutting, etc., After the basic parameters of nozzle were determined, the difficulty of processing was directly influenced by the nozzle type and the length of its divergent section based on the requirements of manufacturability. The gas flow characteristics for micro nozzles with different section shapes and different divergent section lengths were analyzed with the aid of CFD simulation technology, which helped to determine the rules of nozzle type selection and the optimum divergent section length. The simulation results indicate 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 3mm 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.