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A team from the Institute of Fluid Mechanics and Heat Transfer at the Vienna University of Technology (TU) has mathematically analysed what happens when champagne corks are popped for the first time. They supplemented their calculations with images from high-speed cameras - and came up with astonishing results.
While the cork flies away at a speed of around 20 metres per second, the escaping gas overtakes the cork and breaks the sound barrier at a speed of around 400 metres per second. At room temperature, this is 340 metres per second. This creates a shock wave, which significantly changes the pressure conditions in front of the mouth of the bottle. The temperature also changes abruptly as the gas expands. In some places, it can cool down to minus 130°C and even tiny dry ice crystals can form from the CO2 in the sparkling wine. "Different temperatures lead to dry ice crystals of different sizes, which scatter light in different ways. This results in differently coloured smoke. In principle, you can tell the sparkling wine temperature from this colour," explains study author Lukas Wagner.
The bang when a bottle of sparkling wine is opened quickly is not only due to the abrupt expansion of the cork, which creates a pressure wave. The shock wave caused by the supersonic gas jet - comparable to the sonic boom of aeroplanes - also contributes to the characteristic sound.
"We didn't initially expect supersonic phenomena to actually occur when a champagne bottle pops," says study author Bernhard Scheichl. "But as our simulations show, this arises naturally from the equations of fluid mechanics, and our results agree very well with the experiments." The methods developed for the study can also be applied to other areas involving gas flows or ballistic missiles such as projectiles or rockets.
(al / Source: TU Vienna)