Microsecond-level analysis of what happens when we pop a bottle of champagne has revealed how a space rocket takes off, how a freshly fired bullet evolves, and how a gunpowder explosion develops.
Physicists from France and India have simulated the processes that occur when we open a bottle of champagne. The results of this work can help to better understand what happens when rockets are launched or firearms are fired. The study is published in Physics of Fluids.
A type of sparkling wine called champagne is perfect for highlighting the solemnity of any event. Thanks to an excess of carbon dioxide, the opening of the bottle is accompanied by a fountain of foam (which, however, can be avoided), while the glass is decorated with a bizarre set of bubbles.
All of the above would be impossible without the complex physical and chemical interactions that are of interest to scientists. Thus, bottle fermentation is responsible for the formation of carbon dioxide in champagne, which is facilitated by the addition of yeast and sugar.
This gas partially dissolves in the wine, its concentration being related to the temperature and partial pressure of the rest. For this reason, the speed of cork exit depends largely on the temperature of the bottle.
Also interesting is the physics of the gas mixture, consisting mainly of carbon dioxide and water vapor, that comes out of the bottle when the cork is uncorked.
A study using high-speed imaging to see what happens when we uncork a bottle of champagne showed that the gas jets propagate in supersonic mode, after which they undergo adiabatic cooling (no heat exchange with their surroundings) that it can even lead to crystallization of water.
The interaction of supersonic jets with the surrounding atmosphere gives rise to the formation of shock waves of complex organization. In this case, periodic structures are often observed in the jet, caused by the repeated process of its compression and expansion.
This makes opening the champagne sound like a rocket engine, as well as erupting volcanoes and geysers. In the case of cork, however, the description task is complicated by the strong non-stationarity of the whole process, as well as by the mobility of the stopper, which changes along the channel in which the jet propagates.
To understand in more detail what happens to the gas when a bottle of champagne is opened, a group of physicists from India and France, with the participation of Gerard Liger-Belairfrom the University of Champagne – Ardenne, simulated this process using computational fluid dynamics.
The initial calculation area consisted of two spaces separated from each other by the walls of the bottle and the cork. The outer part corresponded to room conditions, the inner part corresponded to the gaseous space between the wine and the cork, with a volume of 35 cubic centimeters filled with carbon dioxide.
The authors accurately transferred the profile of a real bottle to the model and chose the temperature and pressure of carbon dioxide equal to 20 degrees Celsius and 7.5 bar, so that the simulation was consistent with previous experiments. A series of frames indicated the elapsed time in microseconds after the start of the virtual bottle opening.
For their calculations, the physicists considered that the cork moved at a constant speed, equal to 18.6 meters per second, as well as the elasticity of the cork, which gives it the characteristic of a fungus after release. The calculation of the model was simplified by the axial symmetry (around an axis) that a bottle exhibits when placed vertically.
Looking at the simulation results, the scientists identified three stages in the processes of uncorking a bottle of champagne.
In the first stage, which lasts about 600 microseconds, the gas mixture is partially blocked by the cork, preventing the ejected champagne from reaching the speed of sound.
But as the cork breaks free, the gas mixture escapes radially at supersonic speed, balancing its pressure through a succession of normal and oblique shock waves.
In the second stage (600 – 1000 microseconds), the high-pressure gases, formed by bubbles, are initially blocked by the cork, but eventually escape from the bottle at supersonic speed, causing small sonic booms.
Applications beyond champagne
Finally, after a millisecond, the pressure in the bottle drops too low for the jet to travel faster than sound. Then we can serve the champagne in the glass.
The authors point out that the resistance exerted by the cork on the jet, throughout the process, is also found in the interaction of the jet stream and the ground that has been observed, beyond the uncorking of a bottle of champagne, both during the takeoff of a space rocket, and in the interaction of a freshly fired bullet with the environment, as well as in the gases of a gunpowder explosion.
Therefore, this discovery will allow their results to be applied far beyond the physics of opening champagne, in applications ranging from rocket launchers, ballistic missiles and wind turbines, to the manufacture of electronic products and underwater vehicles, according to the researchers.
Computational Fluid Dynamic simulation of the supersonic CO2 flow during champagne cork popping. Abdessamad Benidar et al. Physics of Fluids (in press) (2022). DOI:https://doi.org/10.1063/5.0089774