Collaborative Research: Physics-Informed Background-Oriented Schlieren Tomography of Wildfire-Relevant Combustion

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Wildfires are becoming more and more common as climate change renders much of the world hotter and drier. Besides the destruction of natural resources and animal habitats, wildfires that occur near human populations cause devastating damage to structures, resulting in significant morbidity, mortality, and financial losses. Wildfires are difficult to anticipate and control because they are chaotic, three-dimensional (3D), and extremely sensitive to local atmospheric conditions. Despite their importance to the characterization and control of wildfires, the formation, evolution, and interaction of large-scale vortices, streaks, and whirls in fires remain poorly understood. New measurement strategies are needed to characterize and understand wildfire dynamics and improve predictive models. This project will develop an optical sensor using a network of cameras that can perform time-resolved, volumetric (4D) measurements of wildfire-relevant combustion processes.This work will develop, validate, and apply a novel, quantitative 4D flow visualization diagnostic based on background-oriented schlieren tomography (BOST). By employing a parsimonious representation of the flow field and developing a physics-informed closure for tomographic reconstruction, the research will produce accurate 4D reconstructions of laboratory-scale wildfire event surrogates. Experimental reconstructions will be compared to simulations of the same fires to understand entrainment/topology interactions. Existing BOST algorithms solve a set of coupled inverse problems in multiple steps with non-physical closures and use a coarse representation of the unknown field. The developed method will perform these calculations in one step with an efficient wavelet basis. Further, this work will produce a “physics-informed” BOST closure based on the governing equations of fluid dynamics and combustion, enhancing accuracy and facilitating the quantification of additional fields like temperature and velocity. Simulations and measurements will be cross validated using simple solid fuel fires. Moreover, the refined BOST sensor will facilitate comprehensive characterization of fire dynamics in complex, wildfire-relevant configurations for the first time, leading to a more complete understanding.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.