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.

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

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

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

Physical Problem Materials are subjected to Very High Thermal Fluxes 1-100 MW/m2 Thermochemical oxidation (Thermo-)Mechanical and Dynamical Loads Mechanical and Chemical Reactions with Impacting Liquid and Solid Particles

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

Physics overview

Thermo-Degradation process

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)

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

Arrhenius Law Density Temperature Heating Rate Dependent

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

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

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

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

Energy equation

Energy Equation : Material Enthalpy During Decomposition

Ablation Analysis Verification

Temperature Verification

Density Distribution

Mass Flow Rate of Gas

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

Ablation

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

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)

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