Measurement by digital image correlation of the topography of a liquid interface
Résumé
A non intrusive optical method for an accurate measurement of the instantaneous topography of the interface between two transparent fluids is characterized. This method is based on the analysis of the refracted image of a random dot pattern visualized through the interface. The apparent displacement field between the refracted image and a reference image obtained when the surface is flat is determined using a Digital Image Correlation (DIC) algorithm. A numerical integration of this displacement field, based on a least square inversion of the gradient operator, is used for the reconstruction of the instantaneous surface height, allowing for an excellent spatial resolution with a low computational cost. The main limitation of the method, namely the ray crossing (caustics) due to strong curvature and/or large surface-pattern distance, is discussed. Two examples of applications illustrate this method: The time-resolved observation of the circular waves generated by a water drop impact, and the dynamical wetting of a drop on a glass substrate.
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