Numerical simulation of a colloidal thruster in the droplet regime Original Research Article

Experiments with colloid thrusters have shown their ability to operate in various flow regimes extending from the pure droplet to the mixed ion-droplet regime, and in some cases to pure ion emission. Experimental research on this issue has been done using time of flight techniques which have characterized the specific charge of the extracted species, combined with stopping-potential energy analyses. We address this issue from the numerical perspective by developing a single emitter colloid simulation. In previous papers we have presented results from our numerical model for an axisymmetric colloidal jet [J.A. Carretero, M. Martínez-Sánchez, in: 38th Joint Propulsion Conf. and Exhibit, 7–10 July, 2002, Indianapolis, IN, AIAA-2002-3812, 2002; J.A. Carretero, M. Martínez-Sánchez, in: 28th Internat. Electric Propulsion Conf., 17–21 March, 2003, Toulouse France, 2003]. The numerical simulation models the cone-jet transition region of the colloid jet; starting from the needle to the extractor grid, thus reproducing the typical electrospray experimental configuration. The liquid is modelled as an incompressible viscous fluid with a constant conductivity. A Surface charge relaxation equation is included in the model, and the potential and electric fields in the fluid are solved for. The equations have been simplified by employing a slenderness approximation except for the free surface boundary conditions where the terms have been kept exact. Simulation results have been shown to compare well to experimental data for a variety of liquids, for flows image.