FEATURE ARTICLE
Bubbles and Flow Patterns in Champagne
Is the fizz just for show, or does it add to the taste of sparkling wines?
Guillaume Polidori, Philippe Jeandet, Gérard Liger-Belair
Random Effervescence
As we mentioned previously, random effervescence is mainly due to the presence of cellulose fibers deposited on Champagne glasses. The number and distribution of sites is unpredictable. Indeed, most bubble-generating sites are found freely floating within the Champagne after pouring. Because they move about in swooping patterns and produce off-shooting bubble paths that don’t go straight up, we call these particles fliers. Our recent estimation of the dynamics of these fliers has shown them to be neutrally buoyant on average with regard to the surrounding fluid. In quiescent Champagne, the vertical velocity of a flier can be either positive or negative, depending on its buoyancy parameters and the gas-pocket volume it contains. After rough calculations, we found the free vertical velocity of fliers to range between -0.19 and 0.13 millimeters per second. These values are negligible compared to the fluid velocity, so fliers can make rather good fluid-motion markers.
Because of their high buoyancy, natural bubble nucleation sites can end up being prisoners of the motion they themselves initiated. Time-lapse images of fliers look something like claw scratches, with each lighted filament corresponding to a bubble trajectory. These visualizations are a powerful tool for giving a precise idea of the bubble-emission frequency and wavelength. For example, linear motion in the laser-lighted plane results in a flier print made from the combination of the vertical ascendant motion of bubbles and the linear oblique velocity of a flier. When the flier describes a complex curvilinear travel path, the visualization yields a spectacular result looking like an abstract art painting.
Random effervescence causes bubbles released from fliers to form complex fluid-flow patterns with multiple unsteady cells that evolve over time. For example, an image of the top corner of one glass shows that no less that three eddies occupy a small area, leading to small-scale but vigorous mixing and circulation processes. The cells change in size and location over time according to an arbitrary scheme. Purely chaotic behavior characterizes the flow in random effervescence.
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