超声波电喷推力器羽流中和特性研究

超声波电喷推力器主要应用在小卫星(10 kg)平台,为解决该类型推力器的羽流在中和过程中产生的推力偏角以及能效低的问题,对超声波电喷推力器的羽流中和过程进行数值研究.为实现电喷推力器羽流特有物理过程的仿真,建立了一种带电液滴中和模型(NECD模型),对电子-正电液滴的中和过程进行捕捉,包括带电粒子的输运过程、电子液滴碰撞过程以及液滴的破碎与重组等过程;为验证模型的可行性和精度,开展推力测量和羽流高速照相试验,以工况相同试验和仿真结果进行对比.结果显示,该模型的综合计算误差在20%左右,在不同工况下可以和试验值形成趋势上的符合.基于该计算模型,对放电功率为2 W、放电电流为2 m A的超声波电喷推力器进行羽流输运过程的数值模拟,获得表征羽流中和特性的几种参数分布,包括数密度、电荷密度、液滴体积大小等,并统计出各类能耗所占比例,解释了推力偏角和能效低问题的内在机理以及为相应优化提供参考.

Plume neutralization mechanism for ultrasonically aided electrospray thruster

The ultrasonically aided electrospray thrusters (UAET) are used mainly on micro-satellites (with mass less than 10 kg). In this work, numerical simulation studies of the UAET plume field are conducted to investigate the following two problems encountered during operational tests:the avertence angle of thrust direction, which exists between the design and test outcome, and the lower energy efficiency than the established theoretical value. In order to precisely model the special physical process of the UAET plume neutralization, we develop a new hybrid model named the neutralization of electrons and charged droplets for the plume fluid field to capture the neutralization process of electrons and positively charged droplets. This model describes the dynamical movement of particles, the collision between electrons and droplets, the breakage and coalescence of the droplets, and the flow and heat transfer between the droplets and background gas. To show the feasibility and accuracy of the model, experimental tests involving thrust measurements and high-speed photography of the plume are conducted. The comparison between the test and simulation results under the same study conditions shows that the average error of this model is about 20%, and both the test and calculation exhibit a consistent trend in the various study cases. According to this model, we simulate the plume fluid field of UAET (with 2-W discharge power and 2-mA current) and identify the distribution characteristics of several parameters, including the droplet number density, charge density and the droplet volume, as well as the energy consumption categories that occur. Our model can successfully demonstrate the internal mechanisms that cause the two problems identified above. Our work will provide support for future studies of optimal design.