Multi-physics Modeling of the Ablation Process for Thermal Protection Systems

TECH FOCUS AREAS: Directed Energy; General Warfighting Requirements (GWR) TECHNOLOGY AREAS: Materials OBJECTIVE: These efforts will develop a high-fidelity predictive capability to assess the ablation response of thermal protection system materials based upon first principles multi-physics models. DESCRIPTION: The Air Force is researching materials with high ablation energies for use as thermal protection systems in extreme environments. Modeling the thermal degradation of these materials necessitates the use of an ablation response model (ARM). Traditional ARMs were designed with reentry applications in mind [1] and are not specifically tailored to address strong localized flux variations and the corresponding non-uniform ablation. ARMs typically rely on mass blowing (B-prime) tables to model the chemical reactions at the solid-fluid interface and assume equilibrium chemistry based on partial pressures and temperatures at the surface. B-prime tables can introduce a significant amount of uncertainty into the analysis as often times the required data can be difficult to obtain. Coupling an ARM with computational fluid dynamics (CFD) [2] can eliminate the need for B-prime tables but comes at considerable computational expense. Furthermore, the complex composite materials and surface coatings that are often used in thermal protection systems (TPS) present additional challenges for traditional ARMs. These materials and coatings can result in complex surface reaction mechanisms, which can increase the computational expense of simulation. The Air Force seeks advanced multiphysics tools for modeling ablation of TPS materials in highly non-linear heat flux environments and aero-assisted ablation due to surface defects for high-speed systems. In addition, enhanced tools are needed which can accurately model ablation of non-homogenous composite materials. The tools should require minimal supplemental data (e.g., B-prime tables) and be computationally efficient. PHASE I: The Phase I proposal should focus on demonstrating the feasibility of one or more novel modeling ablation concepts under localized heating or aero-assisted ablation due to surface defects. The demonstrated concept should show an improvement over the state-of-the-art. PHASE II: Phase II will validate the proposed tool using a composite material and non-uniform heat flux profile relevant to Air Force programs. Focus will be on extending the tool to higher fidelity analysis with the goal of modeling ablation due to hypersonic aeroheating through the full flight trajectory. PHASE III DUAL USE APPLICATIONS: In Phase III, the firm will work with industry to make the novel concept widely available for material ablation simulation in a broad range of environmental conditions and materials. Relevant non-military applications may include the simulation of aircraft brake pad performance, rocket nozzle ablation and other high temperature material ablation problems. NOTES: The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the proposed tasks intended for accomplishment by the FN(s) in accordance with section 5.4.c.(8) of the Announcement and within the AF Component-specific instructions. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. Please direct questions to the Air Force SBIR/STTR Help Desk: usaf.team@afsbirsttr.us REFERENCES: [1] Amar, A., N. Calvert, and B. Kirk. Development and Verification of the Charring Ablating Thermal Protection Implicit System Solver. AIAA-2011-0144. 2011; [2] Marschall, J., and M. MacLean. Finite-Rate Surface Chemistry Model, I. AIAA-2011-3783. 2011. KEYWORDS: Ablation; surface chemistry; computational fluid dynamics; multi-physics model; thermal protection systems; composites, hypersonics