Ionic Thruster Diagnostics by Means of PIV and LPT

Particle image velocimetry (PIV) and Lagrangian particle tracking (LPT) by means of shake-the-box (STB) evaluation are presented as complementary experimental techniques for the diagnosis of the momentum-transfer characteristics of ionic thrusters. PIV evaluation enables high-resolution and near-wall velocity fields over a large area for a single wire-to-airfoil electrode pair and delivers accurate thrust readings via the integral momentum equation when fluctuations in the velocity field are accounted for. This is contrast with a differential approach based on the Navier-Stokes equation and leveraging the explicit capability of LPT to measure material acceleration. Wire-to-airfoil and wire-to-grid thruster configurations are tested, showcasing limitations due to optical access and glare, particularly with wire-to-airfoil configurations. The LPT velocity fields agree with the PIV fields, serving as cross-validation. In novel findings, the LPT acceleration fields of the wire-to-grid thruster configuration show channel-like acceleration regions in the drift zone and a major impact of pressure gradients on the thrust generation.