When a bottle of champagne is opened, it is a common sight to see the cork flying out with a pop. While this may seem like a simple everyday occurrence, the physics behind it is quite complex. In a recent study conducted at TU Wien, scientists have used computer simulations to understand the behavior of the stopper and the gas flow during this process. The results of the study have revealed astonishing phenomena, including the formation of a supersonic shockwave and gas flow speeds that exceed the speed of sound. This research not only sheds light on the physics of champagne cork popping but also has implications for other applications involving gas flows.
The gas that flows out of a champagne bottle when it is opened is much faster than the cork itself. While the cork may reach a speed of around 20 meters per second, the gas flow can reach speeds of up to 400 meters per second, exceeding the speed of sound. This results in the breaking of the sound barrier and the formation of a shockwave. When a shockwave occurs, there are abrupt jumps or discontinuities in variables such as pressure and velocity. This creates a point in the gas jet known as the “Mach disk,” where the pressure and velocity have different values on either side of the shockwave. Similar phenomena are observed in supersonic aircraft or rockets, where the exhaust jet exits the engines at high speed.
Another interesting aspect of the champagne cork popping is the abrupt temperature changes that occur. When the gas expands, it cools down, resulting in a temperature drop. In the case of a champagne bottle, this cooling effect can be significant, with the gas temperature reaching as low as -130°C at certain points. This extreme temperature drop can even lead to the formation of tiny dry ice crystals from the CO2 present in the sparkling wine. The size of these dry ice crystals determines the color of the smoke that is released when the bottle is opened. By observing the color of the smoke, one can even estimate the temperature of the sparkling wine.
The characteristic sound of a champagne cork popping is a combination of different effects. Firstly, the abrupt expansion of the cork creates a pressure wave that contributes to the sound. Secondly, the supersonic gas jet generates a shockwave, similar to the sonic boom phenomenon. Together, these two effects result in the audible pop when the bottle is opened. The expansion of the cork was modeled based on experiments conducted during the study. The understanding gained from this research can also have applications in other areas where solid flow bodies interact with fast gas flows, such as firing pistol bullets or launching rockets.
The study conducted at TU Wien has provided valuable insights into the complex physics behind champagne cork popping. By using computer simulations, scientists have been able to understand the behavior of the stopper and the gas flow, revealing the formation of supersonic shockwaves and high-speed gas flow. Additionally, the study has shed light on temperature changes and the formation of dry ice crystals during this process. This research not only explains the phenomena observed in champagne cork popping but also has broader implications for other applications involving fast gas flows.