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Simple distinction of similar-looking inertial particles and fluid tracers on camera images

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Abstract

Dispersed two phase flows cover a wide range of natural phenomenon and technological applications. When studying such complex systems, having access to the velocities of both phases is necessary to fully understand their dynamics. In experiments, inertial particles have to be distinguished from tracers which image the movement of the carrier fluid. For this, most studies rely on differences in size or brightness. This article presents a method for separating particles and tracers if those are of similar size and brightness. It employs fluorescent tracers and a two camera acquisition system. One camera records both particles and tracers, while the second camera only records the tracers by using an optical filter for the fluorescent light. A straightforward image processing algorithm then identifies and removes the tracers from the first image. This allows for the velocities and positions of the particles to be measured in conjunction with the velocity field of the carrying phase. A series of tests are performed on the method to demonstrate its reliability. In addition to ensuring that the method functions in a satisfactory manner, these tests give guidelines on how to use the method correctly. To illustrate an application of this method, measurement results of ceramic particles settling in still water are presented.

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Authors and Affiliations

  1. Institut des Sciences de la Mécanique et Applications Industrielles (IMSIA), ENSTA-Paris / CNRS / CEA / EDF / Institut Polytechnique de Paris, 828 Boulevard des Maréchaux, 91120, Palaiseau, France

    David De Souza, Till Zürner & Romain Monchaux

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  1. David De Souza
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  2. Till Zürner
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  3. Romain Monchaux
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Correspondence to David De Souza.

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This work was supported by the French Direction Générale de l’Armement (DGA) through the Agence de l’Innovation de Défense (AID).

Appendix: Exemplary implementation

Appendix: Exemplary implementation

This section outlines an example implementation of the tracer removal method in MATLAB R2016b. The particle image \(I_\mathrm {P}\) and the tracer image \(I_\mathrm {T}\) are stored in the variables I_P and I_T, respectively, as \((N_1\times N_2)\)-matrices of type uint16. The position of the tracers in \(I_\mathrm {T}\) are detected by a threshold value \(th_\mathrm {T}\) of, for example, 35.

figure b

The variable B_T holds the binarised image \(B_\mathrm {T}\). For the erosion of \(B_\mathrm {T}\), the structure element \(S_5\) is chosen.

figure c

The variable M is a \((N_1\times N_2)\)-matrix of type logical containing the tracer mask \(M\). To calculate the masked particle image \(I_\mathrm {M}\), the mask is applied to \(I_\mathrm {P}\).

figure d

The variable I_M is a \((N_1\times N_2)\)-matrix of type uint16 and contains the image \(I_\mathrm {M}\) with only particles remaining. It can now be further evaluated, for example, by applying a PTV algorithm.

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De Souza, D., Zürner, T. & Monchaux, R. Simple distinction of similar-looking inertial particles and fluid tracers on camera images. Exp Fluids 62, 114 (2021). https://doi.org/10.1007/s00348-021-03195-7

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  • DOI: https://doi.org/10.1007/s00348-021-03195-7

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