The plume produced by the gas flow through the nozzle of a rocket engine or system vent on a spacecraft can contaminate the spacecraft, its sensors, and other nearby apparatus. Current analytical methods patch numerical solutions for the nozzle core flow to those for the boundary layer flow. The resulting continuum solution is then patched to a Monte Carlo calculation for the free-molecular regime. This approach only models steady plumes so that the start-up and shut-down problems cannot be investigated. This project addressed the problem of non-steady plume flows by means of a two-dimensional, fully viscous, non-steady solution for the continuum regime. This numerical method is well-adapted to solving time-dependent flows including viscosity, steep gradients, and even shocks and is, therefore, capable of calculating the fully time-dependent flow of a rocket nozzle during a complete pulse.Phase I demonstrated the feasibility of using the flux-corrected transport (FCT) algorithm with constant viscosity to model non-steady, axially symmetric flow of CO2 in a conical nozzle and in the forward plume region. The computations were validated with experimental nozzle data and were shown to give agreement of better than 7 percent for total pressure, exhaust velocity, and boundary layer thickness as far as 1.5 nozzle diameters downstream. Shutdown flow was also modeled.Potential Commercial Application:PC-based calculation of rocket engine forward and back-flow plumes for axially symmetric nozzles of general shape and simple chemistry in vacuum will be possible.STATUS: Phase I Only
