Research Topics
Mixing:
A central question in scalar mixing consists in offering a satisfactory description of the histogram, or Probability Density Function P(C) of the concentration levels C of the substance being mixed. The question is particularly interesting, and relevant to many applications when the substrate is stirred since in that case molecular diffusion is altered, and in most cases enhanced, by the underlying substrate motions.
Foam Aging:
The bubbles coalescing into each other in an aging foam represent a paradigm for naturally coarsening systems. In a two dimensional foam, the rate of change of a given cell area depends solely on its number of sides as shown by von Neumann (1952). However, the distribution of the cells sizes and its evolution as the foam ages is still an opened issue. Existing experiments on the subject suggest that the distribution of cell surfaces gets broader and broader as the average cell size increases. The environment of a given cell is thus more and more heterogeneous as time progresses.
Gallery
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| A blob of dark ink has been stirred by a rod in a thin layer of viscous fluid. The two-dimensional manifold results in a set of adjacent sheets who rate of diffusive smoothing and coalescence build the overall concentration distribution of the dye. |
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Mixing of a dye discharging from a jet in a square duct. From top to bottom, successive instantaneous planar cuts of the scalar field at increasing downstream locations in the duct showing the progressive uniformization of the dye concentration |
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| A long opened Hele-Shaw cell constantly fed with mono-sized bubbles at the extremity and along which the aging process of the bubble assembly develops spatially (figure above). This kind of "wind tunnel" for foams allows to accumulate statistics and reach convergence of the distributions and other topological quantities at will. |
