CAREER: Understanding the Role of Buoyancy Flow for Accurate and Robust Scale Modeling of Upward Flame Spread

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This project will study how fire behaviors change with scale. Laboratory-scale tests are often used in fundamental research and in technical standards to characterize the burning behaviors of materials. However, key fire behaviors change when moving from small laboratory scale to larger real-world scales found in structures or forest fires. This scalability problem is a long-standing challenge in fire science, one that limits generalizability of laboratory testing. Filling this knowledge gap will improve the relevance of standard safety tests and lead to safer structures and products. Ultimately this will save lives, money, and property for society. This project employs experiments, numerical simulations, and theoretical modeling to control, study, and predict fire behavior at various scales. The focus will be on a phenomenon called buoyancy flow, which varies significantly with scale. The developed scaling models will be validated against real-world testing databases maintained by industry collaborators. This project will also help cultivate the next generation of academic and industry leaders. This will be achieved via interactive public demonstrations of fire dynamics and via promotion of technical standards in college curricula. One of the key factors influencing fire scalability is buoyancy flow. This project will focus on the effects of buoyancy flow on upward flame spread over solids. In this fire scenario, the fuel sample is oriented vertically, along the direction where buoyancy flow varies significantly. The coupling between solid fuel and gaseous flame is sensitive to such buoyancy flow variations, making scalability even more challenging. By nature, buoyancy flow is caused by a density gradient in a gravity field. By systematically varying these phenomena, buoyancy flow can be manipulated. First, the effect of density will be studied by varying pressure and diluents of ambient gas in a combustion chamber. Second, the effect of hyper-gravity will be studied using a 17.7m-diameter centrifuge. Experiments will be augmented by calibrated numerical modeling. The small-scale data, where buoyancy flow is artificially enhanced, will be compared to large-scale data from collaborators, where buoyancy flow is naturally up-scaled with fire size. Dimensional analysis will be performed to identify the invariant dimensionless variable groups. Finally, a new scaling model will be proposed to bridge small and large fires by incorporating buoyancy flow. This will allow creation of fire models that make fewer assumptions than ever before. This will also dramatically increase the applicability of lessons from lab-scale experiments as well as allowing re-interpretation of past reduced-scale experiments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.