The popping of a champagne cork ends up having something in common with a rocket launcher, according to a recent article published in the journal Physics of Fluids. Scientists from France and India used computer simulations to reveal what happens in microseconds after opening a bottle of champagne in detail. They found that in the first millisecond after the cork pops, the ejected gas forms different types of shock waves – even reaching supersonic speeds – before the bubbly calms down and is ready to be absorbed.
“Our paper reveals the unexpected and beautiful flow patterns that are hiding right under our noses every time a bottle of sparkling wine is opened,” said co-author Gérard Liger-Belair of the University of Reims Champagne-Ardenne. “Who could have imagined the complex and aesthetic phenomena hidden behind such a common situation experienced by any of us?”
Liger-Belair could imagine, for example. He has studied the physics of champagne for years and is the author of Uncorked: The Science of Champagne. He gained many insights into the underlying physics by subjecting Champagne to laser tomography, infrared imaging, high-speed video imaging, and mathematical modeling, among other methods.
According to Liger-Belair, the effervescence of champagne arises from the nucleation of bubbles on the glass walls. Once they detach from their nucleation sites, the bubbles grow as they rise to the liquid surface, bursting and collapsing on the surface. This reaction normally occurs within a few milliseconds, and the characteristic popping sound is emitted when the bubbles burst. When champagne bubbles burst, they produce droplets that release aromatic compounds that further enhance the flavor.
Also, the size of the bubbles plays a critical role in a really good champagne glass. Larger bubbles increase the release of aerosols into the air above the glass – approximately 1.7mm bubbles across the entire surface. And the bubbles in champagne “ring” at specific resonant frequencies, depending on their size. Therefore, it is possible to “hear” the size distribution of the bubbles as they rise to the surface in a glass of champagne.
As we reported earlier, champagne is usually made from grapes picked early in the season, when there is less sugar in the fruit and higher levels of acid. The grapes are pressed and sealed in containers to ferment, just like any other wine. COtwo is produced during fermentation, but is allowed to escape because what you want at this stage is a base wine. Then there’s a second fermentation, only this time, the COtwo gets stuck in the bottle, dissolving in the wine.
Striking the right balance is key. You need about six atmospheres of pressure and 18 grams of sugar, with just 0.3 grams of yeast. Otherwise, the resulting champagne will be too flat or too much pressure will cause the bottle to explode. You also need the right temperature, which influences the pressure inside the bottle. This high pressure COtwo it is finally released when the cork is popped, releasing a cloud of gas mixed with water vapor that expands out of the neck and into the ambient air.
Previous experimental work by Liger-Belair and her colleagues used high-speed imaging to demonstrate that shock waves formed when a champagne cork was popped. With the present study, “we wanted to better characterize the unexpected phenomenon of a supersonic flow that occurs during the opening of the champagne bottle,” said co-author Robert Georges of the University of Rennes 1. “We hope that our simulations will offer some interesting clues to researchers , and they can think of the typical bottle of champagne as a mini-lab.”
Based on these simulations, the team identified three distinct phases. Initially, when the bottle is uncorked, the gas mixture is partially blocked by the cork, so that the ejected material does not reach the speed of sound. As the cork is released, the gas can radially escape and reach supersonic speeds, forming a succession of shock waves that balance its pressure.
These shock waves combine to form telltale ring patterns known as shock diamonds (also known as impulse diamonds or Mach diamonds, named after Ernst Mach, who first described them), typically seen in rocket exhaust plumes. . Finally, the ejected material slows down again to subsonic velocities when the pressure drops too low to maintain the required nozzle pressure ratio between the neck and the edge of the stopper.
The research is relevant to a wide range of applications involving supersonic flow, including ballistic missiles, wind turbines, undersea vehicles and, of course, a rocket launcher. “The ground moving away from the launcher as it rises in the air plays the role of the champagne cork on which the ejected gases impact,” the authors explained. “Similarly, combustion gases ejected from the barrel of a gun are launched at supersonic speeds onto the bullet. The problems are faced with the same physical phenomena and can be treated using the same approach.”
DOI: Physics of Fluids, 2022. 10.1063/5.0089774 (About DOIs).