Abstract
This work demonstrates the application of a multi-color LED and a consumer color camera for visualizing phase boundaries in two-phase flows, in particular for particle tracking velocimetry. The LED emits a sequence of short light pulses, red, green, then blue (RGB), and through its color-filter array, the camera captures all three pulses on a single RGB frame. In a backlit configuration, liquid droplets appear as shadows in each color channel. Color reversal and color cross-talk correction yield a series of three frozen-flow images that can be used for further analysis, e.g., determining the droplet velocity by particle tracking. Three example flows are presented, solid particles suspended in water, the penetrating front of a gasoline direct-injection spray, and the liquid break-up region of an “air-assisted” nozzle. Because of the shadowgraphic arrangement, long path lengths through scattering media lower image contrast, while visualization of phase boundaries with high resolution is a strength of this method. Apart from a pulse-and-delay generator, the overall system cost is very low.
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Acknowledgements
The authors would like to thank M.B. Long from Yale University for helping with the use of dcraw and to Alexander Krasowski and Jan Bühnen for help with the measurements. This work was funded by the German Research Foundation (DFG) within SCHU 1369/14 and the Federal Ministry for Economic Affairs and Energy (BMWi) through the AiF/IGF, Project Number 18298 N.
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Menser, J., Schneider, F., Dreier, T. et al. Multi-pulse shadowgraphic RGB illumination and detection for flow tracking. Exp Fluids 59, 90 (2018). https://doi.org/10.1007/s00348-018-2541-0
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DOI: https://doi.org/10.1007/s00348-018-2541-0