VORTEX FORMATION AND STABILITY IN A SCALED GAS-CORE NUCLEAR ROCKET CONFIGURATION

Realistic interplanetary space exploration depends critically upon the development of a high-specific-impulse propulsion system. Previous st udies indicate that the specific impulse of an open-cycle gas-core nuc lear rocket (OCGCNR) might approach 3000 s, Although the OCGCNR is dec eptively simple in concept, it will be difficult to develop in practic e because the core is a uranium plasma that must be nearly totally con fined. Before constructing a more comprehensive model for this engine, there is a requirement to understand the limits of present full-scale simulation models and recent scaled experiments. In this scoping stud y we have used a two-dimensional, axisymmetric, finite difference code to investigate the formation and stability of a recirculation region observed in a scaled experiment, It has been proposed that such a reci rculation region, or vortex, might provide improved confinement of the uranium fuel. Our simulation results indicate that a more comprehensi ve model must treat the rocket nozzle in a self-consistent fashion to properly calculate the confinement of the uranium plasma. Under condit ions that lead to vortex formation, the position of the vortex depends upon the inlet geometry and injection velocity, the nozzle position a nd subsonic convergence angle, the base-bleed injection rate, and turb ulence. With a large base-bleed injection rate, a vortex forms but is then swept away through the nozzle, a result that resolves an inconsis tency between a full-scale engine simulation model and recent scaled e xperiments.