Project Title:

Rigorous Practical Method & Tool for Predicting Plume Backflow &

Aero Optics, Inc.
655 Deep Valley Drive, Suite 335
Rolling Hills Estates, CA 90274

93-1		09.16	1933			Amount Requested $69,986.56

Rigorous Practical Method & Tool for Predicting Plume Backflow & 
Surface Impingement

Abstract:

Spacecraft 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.

The method/tool to be demonstrated under Phase I and 
upgraded/augmented/completed under Phase II is intended for use by 
contamination engineers/analysts and spacecraft 
designers/developers who require rigorous but practical prediction 
techniques for plume impingement effects.  Although intended for 
use in engineering applications, the code also provides state-of-
art capabilities for scientific applications.

Surface contamination, Plume backflow, Multicomponent diffusion, 
Viscous coupling, Flow rarefaction Molecular scattering