CSAR Noon Seminar
Luca Massa,
UIUC/CSAR
DATE: Wednesday, November 17, 2004
TIME: 12:00 Noon
PLACE: 2240 DCL
1304 W. Springfield Ave., Urbana, IL
TITLE: Using Heterogeneous Propellant Simulations to Create Subgrid
Models for Navier-Stokes Analysis of Rocket Motor Chamber Flows
ABSTRACT
This talk centers around computational simulations of heterogeneous
propellant combustion in rocket motor chamber conditions. The
simulations aim at resolving the interaction between the solid phase
morphology and the reactive flow field it supports and analyzing the
importance of multidimensional effects on the burning characteristics.
A comprehensive approach is presented for the analysis of
multidimensional propellant deflagration and the systematic deduction
of subgrid models that take into account a detailed description of the
solid phase. The model allows for a fully coupled analysis of the
deflagration process where the relevant scales associated with the
heterogeneous solid phase, the corrugated surface and the reactive gas
phase are resolved. The gas phase assumes a global kinetic mechanism.
The calibration of the kinetic parameters is transformed into a
optimization problem so that an arbitrarily large amount of information
can be included in the model. In this way new propellant formulations
can be easily considered. Two and three dimensional propellant
computations have been used to validate the model. Surface shape and
time integrated regression rate have been compared with experiments.
Two subgrid models are currently under investigation. The first model
weighs the importance of multidimensional terms in propellant
deflagration. The reduction of the multidimensional equations to a
single dimension by means of spatial averaging, leads to the definition
of non-linear correlation terms. In a subgrid model, the correlations
terms are treated as source terms that determine the deviation from one
dimensional burning. The second modeling effort considers the
perturbations of the flow injected by the solid propellant into the
chamber. Velocity and temperature fluctuations are due to the
propellant morphology. A statistical description of the fluctuations
is obtained through three dimensional computations. The complex
reactive flow generated by the mixing of reactants injected form
distinct locations on the burning surface, is shown to play an
important role in determining the fluctuations scales. The statistical
description can be used to implement stochastic boundary conditions for
a fluid only Navier-Stokes analysis. The results of the fluid analysis
lead to the conclusion that the statistics of the fluctuations affect
primarily the flow in the transition to turbulence region, while the
flow in the fully turbulent region is weakly affected.