A fluid dynamics study using image processing of scallops on dissolving hard candy

The surface morphology of dissolving and/or melting solid bodies in a fluid is of interest in many applications. The surface pattern formation is strongly correlated with the forces exchanged between the fluid and the body. Indeed, on one hand, a solvable body is dissolving in the fluid due to a concentration gradient and/or melting due to a temperature gradient, thus destabilising the fluid boundary layer on its surface. On the other hand, the boundary layer is the major agent in eroding the body surface, through the application of shear forces. Therefore, studies on the topic are useful not only for claryfing the physical phenomena involved, thus enabling more accurate mathematical models, or for increasing the predictability in commercial engineering applications. But also for providing new tools in geomorphology to better estimate the initial fluid flow conditions that gave birth to now visible coherent structures on the surface of underground rocks. Extending the proposed tools from geology to planetary geology, these could even potentially be of critical interest in space missions that aim to ascertain the presence of water on a planet. The results of a parametric experimental study based on the dissolution of hard candy in natural convection are here proposed and commented. The main variable parameters being considered are: -) the inclination of the object, which was tilted at 30°, 45°, 60° with respect to the gravity line; -) the salinity of the fluid. But also the convexity of the surface and the possible presence of V- or U-shaped incisions on the surface are introduced for drawing attention on and suggesting possible future studies. The surface pattern formation of first flutes followed by scallops is confirmed. Thanks to image data processing, a study on the body regression rate and an investigation on the characteristic size and on vertical and horizontal wavelengths of the coherent superficial structures is conducted. The results obtained from the photos are then evaluated according to the hydrodynamic stability theory, which is introduced at the beginning of the present thesis, and are compared to the shapes of coherent structures in wall-bounded turbulence. Final general comments on the results and the work conducted, together with suggestions for possible successive experimental works, are finally provided.