Title:

Modeling Solid Rocket Motors

Speaker:

Dr. Brandon Runnels

Affiliation:

Iowa State University

When:

Wednesday, October 15, 2025 at 11:00:00 AM   Add to Calendar

Where:

MRDC Building, Room 4211

Host:

Ellen Mazumdar
ellen.mazumdar@gatech.edu

Abstract

Solid composite propellants (SCPs) remain central to modern propulsion due to their stability, ease of manufacture, and dual role as structural and energetic materials. Conventional formulations such as ammonium perchlorate/hydroxyl-terminated polybutadiene (AP/HTPB) have been used for decades, yet their composition and fabrication methods have changed little, leaving significant room for performance improvements. With the emergence of additive manufacturing, it is now possible to design rocket motors with arbitrary geometry and tailored composition, motivating the need for predictive simulation of SCP behavior from first principles. In this work, we present a phase-field framework for modeling SCP deflagration, mechanics, and solid–fluid coupling. First, we develop a phase-field model of deflagration and regression, demonstrating its ability to predict burn rates as a function of composition and microstructure, and to reproduce ignition and assisted burn using a surrogate treatment of the gas phase. Second, we establish a diffuse-boundary formulation for quasi-static elasticity, in which mechanical equilibrium is enforced through source terms rather than boundary conditions. A custom strong-form elasticity solver with adaptive mesh refinement is used to capture stress evolution and phase-field fracture during burning. Finally, we extend the framework to solid–fluid interactions by recasting the viscous Navier–Stokes equations in terms of diffuse source terms. The approach is shown to be mathematically equivalent to sharp-interface conditions and stable across a wide range of problems. Together, these developments demonstrate that phase-field methods can provide a unified, predictive platform for the design and optimization of next-generation solid propellants and additively manufactured rocket motors.

Biography

Brandon Runnels is an Associate Professor of Aerospace Engineering at Iowa State University. He received his BS in mechanical engineering from New Mexico Tech, and his PhD in mechanical engineering from Caltech. After completing his doctorate, he joined the faculty at the University of Colorado Colorado Springs for eight years before moving to Iowa State. His research interests lie at the intersection of physics, mathematics, and computer science, developing novel methods for predictive materials and mechanics simulations. His research has been supported by DOD, DOE, and the NSF CAREER program, and ranges in application from damage identification in structural materials to reactive flow simulations in energetic materials.

Notes

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