PSAM 16 Conference Paper Overview
Welcome to the PSAM 16 Conference paper and speaker overview page.
Lead Author: Ashley Coates Co-author(s): Scott L. Lawrence scott.l.lawrence@nasa.gov
Donovan L. Mathias donovan.mathias@nasa.gov
Brian J. Cantwell cantwell@stanford.edu
| Numerical Investigation of Flame Propagation for Explosion Risk Modeling Development |
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| Understanding the risk associated with uncontained rocket engine failures is critical to ensuring the safety of crew, personnel, and equipment. While there are several approaches to conducting probabilistic risk analyses for these scenarios, developing and using an engineering-level risk assessment model informed by numerical simulations and/or experimental data is the most efficient approach. The current engineering-level model used in support of NASA’s Space Launch System (SLS) program requires the flame speed as an input. Understanding the flame speed under different conditions is therefore a key aspect to determining appropriate blast overpressures and drives the need for flame propagation characteristics to be further studied. This numerical study looks to address the need for further flame speed characterization by simulating flame propagation through a hydrogen-oxygen mixture and comparing simulation results with experimental data and engineering model results. The simulations consider variations in initial pressure and velocity distribution to identify influencing parameters on the flame speed and investigate how these parameters may change the way results are used to inform risk assessment models. Pressure and velocity variations are chosen here because they have the potential to vary in full-scale scenarios, but also because in many experimental setups an underlying velocity distribution results from induced recirculation used to ensure a homogeneous mixture prior to ignition. Numerical results for the pressure variation cases show that flame speed increases as pressure increases. This is likely a result of increasing density as well as effects on flame instabilities and building pressure waves in the confined domain. Adding a velocity distribution prior to ignition significantly increased the flame speed throughout the propagation and resulted in non-constant flame speeds as the flame interacted with underlying flow features. Specific fill and recirculation parameters used in the experiment were unknown, so no specific conclusions are drawn about the comparisons with the simulations that included an underlying velocity. However, it is clear the presence and character of a non-uniform velocity field at ignition can significantly affect the subsequent behavior and should be characterized. Comparisons with the engineering model show overpressure is well captured by the model for a given flame speed, but additional flame speed input is needed for non-quiescent scenarios. We conclude that the initial conditions have a non-negligible effect on the flame speed and should be carefully reported for all numerical and experimental studies so that the results can be applied appropriately in risk assessment models. Because the model depends on flame speed as an input, it is critical that these initial conditions are accounted for when modeling different scenarios. Knowledge of these effects ultimately improves risk assessments for rocket engine bay risk analyses, but also for any relatively confined industrial setting where explosion hazards exist. The final paper will include details regarding the CFD simulation process and results, comparisons of the CFD results with a simplified 1-D model being used for vapor cloud explosions for the SLS program, and a summary of conclusions based on the findings. |
Paper AS75 Preview
Author and Presentation Info
Lead Author Name: Ashley Coates (ashley.m.coates@nasa.gov)
Bio: Ashley Coates is an aerospace engineer in the Computational Physics Branch at NASA Ames Research Center. She has spent the last 4+ years on the Engineering Risk Assessment (ERA) Team, largely focused on performing computational combustion analyses in support of Space Launch System abort environment characterization. She also supports physics-based probabilistic risk assessments with a variety of applications, including asteroid threat assessment activities and micrometeoroid impact analyses. Ashley received her B.S. in Aerospace and Mechanical Engineering from the University of California, Davis and her M.S. and Ph.D. in Aeronautics and Astronautics from Stanford University.
Country: United States of America
Company: NASA
Job Title: Research Aerospace Engineer
Bio: Ashley Coates is an aerospace engineer in the Computational Physics Branch at NASA Ames Research Center. She has spent the last 4+ years on the Engineering Risk Assessment (ERA) Team, largely focused on performing computational combustion analyses in support of Space Launch System abort environment characterization. She also supports physics-based probabilistic risk assessments with a variety of applications, including asteroid threat assessment activities and micrometeoroid impact analyses. Ashley received her B.S. in Aerospace and Mechanical Engineering from the University of California, Davis and her M.S. and Ph.D. in Aeronautics and Astronautics from Stanford University.
Country: United States of America
Company: NASA
Job Title: Research Aerospace Engineer