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Abstract
Historically, the fire safety qualification of materials for space vessel use has been expensive, time constrained, and parametrically limited. These challenges stem from the distinct behavior of flames in microgravity and the need to replicate such an environment.
The Narrow Channel Apparatus (NCA) is a horizontally oriented flow duct with a vertical gap height optimized to minimize buoyant flow in standard Earth conditions. The minimization of buoyancy simulates the flow field that is experienced in a microgravity environment, and for this reason the NCA is being considered as a replacement or complement to the current NASA-STD-6001 Upward Flame Propagation Test.
This work focuses on numerical modeling of a quasi-steady opposed flow flame over polymethyl methacrylate fuel in an NCA with a regressed fuel surface. A model was developed in ANSYS Fluent which includes laminar flow, species transport, a single-step finite-rate reaction, and associated heat transfer. Additional customizations were made to the model to improve material properties, boundary conditions, and mass flux rate feedback from the regressed fuel surface into the channel. The fuel surface regression profile is prescribed for each opposed flow velocity based on experimentation performed at Michigan State University (MSU).
Variable opposed flow velocities between 10 and 50 cm/sec, as well as sensitivity to gravity and solution convergence settings were studied. Detailed post-processing analysis was conducted with respect to both peak and global distribution of flame characteristics, as well as boundary fluxes. It was found that the results showed no sensitivity to gravitational effects, which indicates that the NCA is effectively mitigating the buoyant flow for the opposed flow velocities studied. Results showed good qualitative comparison with the existing literature, and the groundwork is laid for future development and improvement of the numerical model.
