激光烧蚀掺杂金属聚合物推力产生过程数值模拟

Numerical Simulation of Thrust Generation Process of Laser Ablating Polymer Doped Metal

关键词:  激光烧蚀推进  掺杂聚合物  推力产生机理  数值模拟

Key words:  Laser ablation propulsion  Doped polymer  Thrust generation mechanism  Numerical simulation

摘要:

为了增进对激光烧蚀推进中推力产生过程的认识，建立了激光烧蚀掺杂聚合物推力产生过程的模型，发展了一套包括激光能量沉积、工质烧蚀、烧蚀羽流飞散等过程的数值仿真程序。数值计算了真空中3～40J/cm2激光烧蚀掺杂微米铝颗粒聚甲醛工质的推力、烧蚀轮廓及质量、压强分布和比冲特性，且比冲与实验数据较吻合。计算结果表明:高激光能量密度(30.0J/cm2)较低激光能量密度(5.0J/cm2)的金属颗粒剥蚀情况严重；低激光能量密度(5.0J/cm2)下推力时间变化规律较简单，总体呈现先增后减的趋势，且从整体上看只有一个压强峰值；而相对较高的激光能量密度(30.0J/cm2)下，由于存在“烧蚀-屏蔽-烧蚀被削弱”的制约关系，推力时间变化规律复杂；流场产生的高压区较多，且呈现交替产生、并存发展到衰减消失的规律；羽流与激光的相互作用更为剧烈，峰值压强也更大。

Abstract:

In order to improve the understanding of thrust generation process in laser ablation propulsion，a thrust generation model of laser ablating doped polymer was established，and a numerical simulation program considering the process of laser energy deposition，propellant ablation and expansion of ablation products was developed. Characteristics of thrust，ablation profile，ablation mass，pressure distribution and specific impulse of laser ablating polyoxymethylene (POM) doped micro-scale aluminum particles between the laser fluence of 3～40J/cm2 in vacuum were calculated numerically，and the obtained specific impulse shows a good agreement with the corresponding experimental values. The numerical results show that the erosion of metal particles under a higher laser fluence (30.0J/cm2) is severer than that under a lower laser fluence (5.0J/cm2). The curve of the temporal variation of thrust is simple，demonstrating a trend of first rise and then declining with only one pressure peak as a whole under the 5.0J/cm2 case. By contrast，the curve of the temporal variation of thrust under a higher laser fluence (30.0J/cm2) is more complex because of the relationship of‘ablation-shielding-weakened ablation’during the laser ablation process. Moreover，the number of high pressure zones is much more than that under a lower laser fluence of 5.0J/cm2. Under the 30.0J/cm2 case，it shows a trend of alternate generation，coexistence，development，and eventual dissipation. Thus，the interaction between the ablation plume and the laser is stronger，and the peak pressure is much bigger as well.