Champagne bottles open at supersonic speed, urban canyons prolong sonic booms, Earth’s magnetic field will not reverse soon

Supersonic: gases escape very quickly from a champagne bottle. (Courtesy: Shutterstock/Lukas Gojda)

Opening a bottle of good champagne is one of life’s great delights and it is a process that also involves a lot of physics — from the nucleation of tiny bubbles in the fluid to the formation of a cloud of gas at the bottle opening. Now, Gérard Liger-Belair from Université de Reims Champagne-Ardenne and colleagues have studied the uncorking process in more detail, focussing on what happens in the few milliseconds after a bottle has been opened.

In 2019, research by the group showed, for the first time, the formation of shock waves in the fluid during cork popping. Building on that work, the team have now found that a succession of normal and oblique shock waves combine to form so-called “shock diamonds”. These are patterns of rings typically seen in rocket exhaust plumes. This results in the gas mixture escaping from the bottle at supersonic speeds.

“Our [research] unravels the unexpected and beautiful flow patterns that are hidden right under our nose each time a bottle of bubbly is uncorked,” says Liger-Belair. “Who could have imagined the complex and aesthetic phenomena hidden behind such a common situation experienced by any one of us?” At least it offers another excuse to open that bottle of vintage champagne.

The research is described in Physics of Fluids.

Urban canyons

Large cities, particularly those in the Americas, often have urban canyons of tall buildings that can have a significant effect on local wind conditions. But now researchers at France’s University of Lyon have shown that these canyons can affect how sonic booms propagate through urban areas. They have used fluid dynamics simulations to model how booms reflect from buildings and street surfaces.

“With these simulations, we were able to determine the ground pressure signals due to sonic boom propagation and reflection over the buildings and deduce noise levels,” said Lyon’s Didier Dragna. “We can thus predict the noise annoyance felt by the population due to sonic booms.”

While urban canyons did not appear to make sonic booms louder, the simulations suggested that the events lasted for longer times because of resonant effects caused by buildings. The team reports its results in The Journal of the Acoustical Society of America.

Pole reversal

Finally, if you are one to worry that the Earth’s magnetic poles are about to reverse you can now rest easy. Andreas Nilsson at Lund University in Sweden and colleagues have studied an anomaly in Earth’s magnetic field in the South Atlantic Ocean, where the field strength is decreasing rapidly. Some scientists had suggested that this is a harbinger of a pole reversal – something that happens about every 400,000 years.

But Nilsson and team have looked at magnetic field data dating back 9000 years and found that events like the current South Atlantic anomaly are more common than previously thought. The researchers reckon the anomaly will fizzle out in a few hundred years – and a pole reversal is not imminent.

They describe their research in Proceedings of the National Academy of Sciences.

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