1. Fabrice Laturelle, Snecma Moteurs
MSC.Marc-ATAS Advanced Thermal Analysis Software for Modeling of Rocket Motors and Other Thermal Protection Systems
Fabrice Laturelle, Snecma Moteurs
Sophie Fiorot, CS-SI
Ted B. Wertheimer, MSC.

2. Project Overview
The objectives of this work is to develop new software and procedures for the analysis of thermo-structures and thermal protection systems.
This is a three year project focused on :
Thermal Degradation of Materials
Complex Thermal Boundary Conditions
Ablation / Erosion of Materials
Radiation
Numerical Efficiency
Easy of Use, Reduced Time for Data Preparation

3. Background Snecma Moteurs, Solid Rocket Motors Division
40+ years developing, testing, and manufacturing
Solid propellant rocket motors
Thermal protection systems for reentry vehicles

4. Design Objectives
Replace the need for destructive full scale motor tests with precise numerical models
Reduce time / costs for design / analysis
Implement several complexity levels of advanced poro-thermal models
Replace multiple 1-D and 2-D in-house developed special purpose programs with a single, easy to use, maintainable, comprehensive 3-D program
Open the way for future coupling with CFD and radiative heat transfer codes, and fully coupled thermo-poro-mechanical analysis

5. Physical Problem Materials are subjected to
Very High Thermal Fluxes MW/m2
Thermochemical oxidation
(Thermo-)Mechanical and Dynamical Loads
Mechanical and Chemical Reactions with Impacting Liquid and Solid Particles

6. Composite Materials Carbon/Carbon Carbon/Phenolic Silica/Phenolic
Ceramic Matrix composites
Rubber and Reinforced Rubber
Low Mass Thermal Insulators

7. Physics overview

8. Thermo-Degradation process

9. Modeling Levels Level 1 Level 2 Level 3
Simplified Homogeneous Material Model
Effective Specific Heat which is Dependent on the Thermal Loading Path
Level 2
Mass Loss due to Pyrolysis
One Dimensional Fluid Flow
Advanced Material Behavior
Level 3
Three Dimensional Fluid Flow (Darcy Law)

10. Advanced Material Model
Pyrolysis of Material
Mass Density Controlled by Arrhenius Law
Thermal Properties Change based upon a Kachanov Model between Virgin and Charred State
Energy absorption and internal convection
Water Vapor Creation
Coking
Carbon comes out of the Pyrolysis Gases and Deposits onto the Solid

11. Arrhenius Law
Density
Temperature
Heating Rate Dependent

12. Arrhenius Law for jj
Dimensionless variable jj that goes from 1 to 0 during pyrolysis : calculated by a law of Arrhenius:

13. Surface Energy Balance
wall
flow
convection
conduction
decomposition
ablation by particles
ablation by gases
radiationbalance
particles impact
diffusion
blowing

14. Ablation Thermochemical Ablation (Gases, Particles) Mechanical Erosion
Due to impacts of particles
Due to other actions such as the shear stress of the flow and vibration of the part

15. Mass Balance Equation
The mass equation of standard level 2 model is the mass equation of the gas, written in the stationary state, with a source term of decomposition.
mass flow rate of the gases of decomposition.
source term of decomposition

16. Energy equation

17. Energy Equation : Material Enthalpy During Decomposition

19. Ablation Analysis Verification

20. Temperature Verification

21. Density Distribution

22. Mass Flow Rate of Gas

23. Rezoning Issues Shaver Mesher Relax Mesher
Rezone outer element during recession when necessary
Update values associated with exterior SIP based upon recession
Shift SIP when outer element removed
Remove number of SIP points
Relax Mesher
Rezone complete mesh
Update all SIP value
Number of SIP points remain the same

24. Ablation

27. Thermal Contact Expansion of MSC.Marc Capabilities for Thermal Contact
No Contact
Thermal Convection to the Environment
Close Contact
Convection, Radiation Between Surfaces
True Contact
Conduction

28. Thermal Contact If dist < d1 then thermal conduction
If d1< dist < d2 then near contact
If d2 < dist then no contact
Q = hcv*(T2-T1)+hnt*(T2-T1)ent +
sigma*eps*(T24-T14) +
(hct – (hct-hbl)*gap/dqnear)*(T2-T1)

29. Conclusions
Advanced Thermal Analysis Capabilities Suitable to High Temperature Applications are Being Added to MSC.Marc
Excellent Correlation has been Observed
Increase Capability , with Less Costs
Implementation of level 3 poro-thermal model, advanced radiation capabilities, and testing, are still in progress