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01-01-2024

Champagne bottle cork "pop" involves supersonic speed

At first glance, opening a bottle of champagne seems straightforward: high pressure within the bottle forces the cork out with a loud pop. However, according to new research, the seemingly simple act of popping a champagne cork involves supersonic speed.

A study led by Lukas Wagner, a doctoral student at Vienna University of Technology‘s Institute of Fluid Mechanics and Heat Transfer, reveals the complex interplay of physics behind the pop of a champagne bottle.

Mathematical-numerical analysis 

While high-speed cameras had previously captured the act of a champagne cork popping, a detailed mathematical analysis was missing. 

Researchers at TU Wien used intricate computer simulations to precisely model the behavior of the cork and the gas flow during uncorking.

Supersonic phenomena 

The results of the analysis are astonishing. A supersonic shock wave forms as the gas escapes the champagne bottle, reaching speeds of over 1.5 times the speed of sound. 

These findings, published on the pre-print server arXiv, hold significant implications beyond the realm of champagne, including gas flows around ballistic missiles, projectiles, or rockets.

Understanding the shock wave

Wagner explained that while the cork flies away at a modest speed of about 20 meters per second, the gas flow is much faster, exceeding 400 meters per second. This rapid flow overtakes the cork, breaks the sound barrier, and creates a shock wave. 

Unlike regular gas flow, where pressure and temperature change gradually, a shock wave induces sudden jumps in these variables, creating a phenomenon known as the “Mach disk.” This discovery aligns with similar occurrences observed in supersonic aircraft or rockets.

Dramatic temperature drop

An unexpected aspect of this phenomenon is the dramatic temperature drop. Wagner noted that the expanding gas in the champagne bottle can cool down to as low as -130°C, sometimes forming tiny dry ice crystals from the CO2 in the sparkling wine. 

“This effect depends on the original temperature of the sparkling wine,” said Wagner. “Different temperatures lead to dry ice crystals of different sizes, which then scatter light in different ways. This results in variously colored smoke. In principle, you can measure the temperature of the sparkling wine by just looking at the color of the smoke.”

Cork expansion and the audible pop

“The fact that supersonic phenomena actually occur when a bottle of sparkling wine pops was anything but clear at first – you wouldn’t necessarily expect it,” said Bernhard Scheichl, Wagner’s dissertation supervisor. “But our simulations show that this arises quite naturally from the equations of fluid mechanics, and our results agree very well with the experiments.”

The characteristic popping sound combines the cork’s abrupt expansion, creating a pressure wave, and the shock wave from the supersonic gas jet. This acoustic blend is comparable to the sonic boom experienced in aeroacoustics.

Broader implications

The methods developed through this research offer insights into other technical areas involving solid flow bodies interacting with high-speed gas flows, such as the firing of pistol bullets or the launching of rockets. 

The research at TU Wien not only provides a deeper understanding of the dynamics behind popping champagne but also paves the way for advancements in various technological and scientific applications.

Essentially, the study of a simple champagne cork pop opens up a window to understanding complex fluid dynamics in various fields.

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