Tomographic Background-Oriented Schlieren Facility for Buoyancy-Driven Flows and Flames

This paper presents the design, development, and experimental demonstration of a tomographic background-oriented schlieren (BOS) facility tailored for investigating buoyancy-driven flows and low-speed combustion dynamics. The facility is optimized to achieve high sensitivity to deflections, minimal image blur, and sufficient temporal and spatial resolution for capturing transient phenomena. The design prioritizes a balance between the number of views, joint field of view within the flow domain, and imaging rate. These trade-offs guide the selection of system parameters, including camera-to-flow and flow-to-background distances, lens focal length, and background plate placement. An 11-camera configuration was chosen, supported by a systematic optimization of these parameters. High-powered LEDs provide back-illumination to minimize quasi-shadowgraph artifacts, while synchronization between fast square-wave LED pulses and camera exposures ensures sharp, time-resolved imaging. Initial experimental testing using a candle plume demonstrates the potential to capture 3D dynamics of buoyant, reacting flows with this facility. Tomographic reconstructions reveal coherent structures, fine-scale flow features, and temperature variations consistent with prior findings. These results establish the facility as a robust diagnostic resource for studying solid-fuel combustion and air entrainment dynamics, with future work aimed at enhancing reconstruction fidelity and extending applications to complex combustion scenarios.