Cambridge scientists solves whistling kettle mystery

Scientists at Cambridge University have solved the age-old mystery of why a kettle whistles when it comes to a boil.
It is down to the speed at which swirls of steam are funnelled through the kettle's spout as the water reaches boiling point, a study at the elite university has found.
As the steam jet becomes greater as it is forced through the small opening it begins to vibrate and vortices are created and as the frequency increases, the steam jet makes sonic alerts, the Sunday Telegraph reported.
The finding might sound trivial, but is expected help solve other annoying problems such as the knocking sound generated by trapped air in plumbing pipes or damaged car exhausts.

"Pipes inside a building are one classic example and similar effects are seen inside damaged vehicle exhaust systems. Once we know where the whistle is coming from, and what's making it happen, we can potentially get rid of it," said scientist Ross Henrywood.
Engineers located the physical source of the tea-kettle whistle at the spout as steam flows up it and identified a two-mechanism process of whistle production.

Results show that as the kettle starts to boil, the whistle behaves like a Helmholtz resonator - the same mechanism that causes an empty bottle to hum when you blow over the neck.

However, above a particular flow speed, the sound is instead produced by small vortices - regions of swirling flow - which, at certain frequencies, can produce noise.
The study tested a series of simplified kettle whistles in an apparatus by forcing air through them at various speeds and the findings are published in the journal 'Physics of Fluids'.