Rigorous, Practical Method for Predicting Plume Backflow and Surface Impingement
Small Business Information
Aero Optics, Inc.
655 Deep Valley Drive, Suite, 335, Rolling Hill Estat, CA, 90274
G. Newton Freeman
AbstractSpacecraft surface contamination can result from nozzle-exhaust molecules, droplets, and/or condensate-clusters which expand and scatter to fill the space volume at large angles from the nozzle thrust axis. Only a small fraction of the exhaust products expands to large angles; however, the amount is sufficient to influence the design and performance of spacecraft sensor platforms which are subject to contamination effects. The large-angle plume mass/species distribution functions depend on 1) the interacting effects of pressure/shear forces and diffusion/rarefaction effects during the rapid angular expansion at the nozzle lip and 2) the nozzle boundary layer characteristics upstream of the lip expansion. Current prediction methods include 1) method-of-characteristics for continuum regions and 2) direct simulation Monte Carlo (DSMC) techniques for transitional regions. Composite predictions are cumbersome to implement; extremely high grid resolutions are required to preclude numerical diffusion across steep gradients. A new formulation is proposed which uses an extended form of the Navier-Stokes equations in flow-conformal curvilinear streamtube coordinates (to minimize numerical diffusion effects) with additional source/sink terms (to account for flow rarefaction effects). The formulation provides a unified continuous prediction capability which bridges from the continuum region of the nozzle interior to the rarefied region of the plume backflow.
* information listed above is at the time of submission.