A vendor's tea kettle seen against the India Gate in New Delhi on Thursday.
A team of engineers including an Indian origin researcher has produced a breakthrough in breakfast musings with the world's first accurate model of the whistling mechanism inside the classic stovetop kettle.
Despite decades of brewing tea in a whistling kettle, the source and mechanism of this siren sound of comfort has never been fully described scientifically. Acknowledging the vibrations made by the build-up of steam escaping through two metal spout plates is about as far as the explanation went – and was good enough for most people.
But not for a team of engineering investigators at the University of Cambridge in England, who have at last illuminated the mystery through a series of experiments.
They have located the physical source of the teakettle whistle at the spout as steam flows up it, and identified a two-mechanism process of whistle production.
Their 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 findings are potentially able to explain familiar problems of other wayward whistles, such as the annoying plumbing noises caused by air trapped in pipes or damaged car exhausts.
To interrogate kettle whistles, Henrywood, working with his academic supervisor, Anurag Agarwal, tested a series of simplified kettle whistles in an apparatus by forcing air through them at various speeds.
The pair recorded the resulting sounds produced by rushing air, plotted the frequency and amplitude data of the sound, then analysed it to identify trends in the data. They also used a two-microphone technique to determine frequency inside the spout.
The study is published in the journal Physics of Fluids.