高背压超声气体团簇喷流中团簇平均尺寸沿喷流方向演化研究

Evolution of average cluster size in supsonic cluster jet under high gas backing pressure

本文通过对高背压(50 bar,1 bar=1.0×105Pa)氩气经长锥型喷嘴(长度L=30 mm)向真空绝热膨胀所形成的超声气体团簇喷流的数值模拟,分析比较了由喷嘴喉口起沿喷流方向在喷流中心轴线上团簇平均尺寸的演化情况.结果表明:沿喷流方向团簇平均尺寸显示先增长后趋于饱和的变化趋势,具有较大尺寸团簇的区域出现在距离喷嘴喉口大约20 mm.据此本文再结合关于喷流中原子密度沿喷流方向变化的模拟结果开展了锥形喷嘴长度的优化研究.针对由常见构型的锥形喷嘴(喉径～0.5 mm,半张角～8.5?)在高背压下形成的团簇喷流,20 mm左右的长度为锥形喷嘴的适宜长度.

Evolution of the average cluster size at the center of a cluster jet from the nozzle throat along the gas flow is investigated using simulations. The simulation is performed for the cluster jet from the expansion of Ar gas into vacuum through a long conical nozzle （with the length L of 30 Mm） under a high backing pressure （～5 ×10^6 Pa）. Results indicate that the cluster size increases gradually until it is close to the maximum with the increase of the distance from the nozzle throat, and the part of the jet with large-size clusters is located at the distance greater than 20 mm from the nozzle throat. Based on the simulation results about the evolution of the cluster size and the atom density in a cluster jet, the optimization of a nozzle length has been discussed under a given condition. This work shows that a proper nozzle length is about 20 mm for a usual conical nozzle with an opening angle of about 8.5 degree and a throat diameter of about 0.5 mm.