3D surface reconstruction of liquid structures in sprays using structured illumination and phase demodulation
Adrian Roth  1, *@  , Edouard Berrocal  1@  
1 : Lund University, Department of Physics, Division of Combustion Physics, Lund, Sweden
* : Corresponding author

The accurate surface reconstruction of 3D liquid structures is an important aspect for the understanding of spray formation and liquid breakups. In this article, an approach to image in 3D the surface of liquid structures in sprays (such as ligaments, liquid sheets/cores and liquid blobs) is presented. The technique is named Fringe Pattern - Laser Induced Flourescence (FP-LIF) which is used by illuminating the liquid structures using a laser interference fringe patterns. By doping, at high concentration, the injected liquid with a fluorescent dye (here fluorescein) a fluorescence signal can be generated very close to the liquid surface. Then, this signal is recorded at a backward angle where the incident modulation encodes the information of the third surface coordinate for each pixel. The recorded 2D images are phase demodulated using the Continuous Wavelet Transform (CWT) and the 3D surface coordinates can be retrieved. In the first part of the presented work, simulated liquid surfaces are considered for parameter optimization of the 3D reconstruction and to evaluate the CWT implementation. It is found from the simulated results that the optimum fringe pattern period sampling is 4 − 7 pixels. In the second part, the technique is applied for two experimental cases of a pending drop and for an onion shaped liquid sheet. To conclude, both the simulated and experimental results show promising 3D reconstructions of liquid surfaces providing a new type of data, which in the future can be used for the validation of computational models simulating liquid breakup.

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