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a b s t r a c tThis paper presents a set of gaskinetic solutions to the problem of unsteady collisionless round plume development: startup and development to a steady flow; steady flow; and shutting down from a steady flow. This can find applications in studying similar transient plume flows from space propulsion devices. Different from many past studies, here we consider the general situation that the average exit gas speed can be larger than zero, and detailed geometry of the nozzle exit radius is included. A fundamental space-velocitytime relation is adopted in this study and it plays a crucial role to obtain the complete flowfield properties of density, velocity, pressure and temperature. This study reveals that there are some internal complementary relations on density and momentum among these three processes. The results involve complex integrations involving factors of time, geometry, and specific speed ratio. Several numerical simulations with the direct simulation Monte Carlo method validate these analytical exact results.Published by Elsevier Ltd. on behalf of IAA

Field emission electric propulsion (FEEP) thrusters are useful as µN, µ-rad attitude control devices for satellites due to their very high potential specific impulse. FEEPs generate thrust by application of a strong electric field to pull liquid propellant such as indium off a tungsten needle. However, this thrust can vary significantly depending on whether ions or droplets are emitted from the needle tip. In this study, we simulate in 2D the emission of charged indium droplets from the tip. The boundary integral method (BIM) is used to rapidly and accurately calculate the electric field on the fluid surface, which is then advected forward in time using level sets. The effects of surface tension, viscosity, electrode location and electric field on the evolution of a droplet are analyzed.

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