Effect of electric field on droplets extraction in Ultrasonic Electric Propulsion system

Abstract

As a novel propulsion technology, Ultrasonic Electric Propulsion is mainly applied to micro-satellite platforms (<10 kg). Due to multi-physics impacts existed in this process such as ultrasonic vibration, electrostatic field and fluid mechanics, study of the influence of electric field on droplets extraction in Ultrasonic Electric Propulsion faces huge challenges. In this work, this problem is investigated by experimental and numerical methods. An ultra-high speed imaging technique is employed to shoot the extraction process of charged droplets, and the droplet extraction process is simulated through using the Coupled-Level-Set/Volume-of-Fluid and Direct Electro Hydro Dynamics methods, aiming to investigate the influence of extraction voltage on the micro characteristics of droplet extraction. In our experiments, the imaging system accurately obtains the images of extraction droplets at different voltages, and the experimental results indicate that the quantity of emission droplets increase with the extractor-emission surface voltages. In the case of a higher voltage, the variability of droplet size is larger than that in a smaller voltage. Numerical results reveal that liquid cone will be stretched longer at a higher voltage before separation. At the same time, more than one droplets are extracted in a single period in this condition, which can account for more extracted droplets in the experiments at a higher voltage. Furthermore, as dual-droplet emission mode or even three-droplet emission mode emerge at a higher voltage in a single emission cycle, the former extracted droplet affects the latter ones and results in differences of their sizes, which further deeply affects charge-mass ratio of charged droplet.