DEPARTMENT OF THE AIR FORCE SMC REGULATION 800-19
Headquarters Space and Missile Systems Center (AFMC)
Los Angeles Air Force Base, California 90009-2960
Multi-dimensional Interactive Gas Flow/Grain Structural Analysis
Solid Rocket Motors
This regulation establishes policies and procedures and assigns responsibilities for SMC program offices to implement multi-dimensional interactive gas flow/grain structural analysis for segmented or monolithic solid rocket motors (SRM) with full or partial cylindrical perforated grain.
1. Policy All SMC space programs shall obtain a multi-dimensional interactive gas flow/grain structural analysis for all new designs and for all modifications to existing designs involving solid rocket motors.
a. Solid rocket motors may be susceptible to failures due to an unstable propellant grain deformation and combustion gas flow interaction. A simple one-dimensional, non-interactive gas flow and grain structural analysis can not properly account for interaction between internal gas flow and grain deformation. This could lead to an anomaly or failure of a full-scale solid rocket motor during motor operation.
b. Detailed multi-dimensional interactive gas flow/grain structural analysis provides potential characterization of these failure modes. The analysis should identify any flaw in the motor and nozzle internal geometry, propellant grain design, propellant properties and other related areas. This analysis is needed for new motors and for existing hardware involving modifications in motor and nozzle internal geometry, grain design, propellant properties and other substantive changes that affect the motor internal flow field.
3. Responsibilities and Procedures
Top Level - A multi-dimensional interactive gas flow/grain structural analysis shall be performed for all new designs and for all existing designs involving modifications. Modifications are defined as any significant changes in motor and nozzle internal geometry, propellant grain design, inhibitor/restrictor characteristics and propellant formulation or processing. The gas flow analysis will determine the pressure load on the grain surface. The pressure load will then be used in a grain structural analysis to determine grain deformation, which in turn induces the change in gas pressure distribution inside the motor. The coupling effect of gas pressure load and grain deformation in a multi-dimensional space is an important part of the interactive analysis. This effect shall be investigated to the full extent until sufficient grain surface recession allows the interaction to be de-coupled. The analysis shall be performed for the most severe motor operating conditions.
Gas Flow Analysis - A full Navier-Stokes solution in a multi-dimensional space shall be obtained in the gas flow analysis of segmented or monolithic solid rocket motors with full or partial cylindrical perforated grain. High fidelity solutions are required during motor ignition and shortly after the ignition, when the interaction effect of gas pressure load and grain deformation is the strongest. The gas flow analysis shall be completed to determine the gas pressure and velocity distribution inside the motor chamber and nozzle.
Grain Structural Analysis - The grain structural analysis shall consider propellant visco-elastic behavior including effects such as creep, pressure and temperature. The initial grain geometry shall account for deformation caused by the grain slump from gravity and thermal shrinkage from propellant curing. Subsequent burn-back geometry will include the deformation caused by internal gas pressure load in a time-incremental analysis. Deformations, stresses and strains resulting from the grain structural analysis shall be used to determine flow constriction potential and grain structural integrity.
The input data, assumptions, rationales, methods, references, summary of significant analysis results and other supporting data shall be delineated in an interactive gas flow/grain structural analysis report.
c. Each SRM program office shall require their contractor to perform an analysis and prepare a report as stipulated in paragraphs 3.a and 3.b and require the first submittal to the program office no later than PDR or other first design review.
d. Each SRM program office shall review and approve the analysis and report, or require re-submittal prior to accepting the proposed design.
e. Each SRM program office shall make provisions for revision of the analysis and report every 12 months throughout the life of the program.
f. Instructions for applying and executing this regulation are provided by SMC Regulation 540-15 (Systems Engineering Policy). Any program director who does not apply and execute this regulation, as required by SMCR 540-15, shall immediately request a waiver from the Commander.
Edward P. Barry, Jr.
Lieutenant General, USAF