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