Whither the teakettle whistle: Breakthrough in breakfast musings

November 15, 2013, American Institute of Physics
Whither the teakettle whistle
Engineering researchers at England's University of Cambridge have studied the fluid dynamics of the steam teakettle and revealed a two-mechanism process of sound production. This breakthrough in breakfast musings can also be applied to wayward whistles, such as annoying plumbing pipe noises. Credit: AIP Publishing

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, the team has produced a breakthrough in breakfast musings with the world's first accurate model of the whistling mechanism inside the classic stovetop kettle. Their paper appears in the journal Physics of Fluids.

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.

Hey, it's not as if people haven't been trying to figure this out for more than a century. In 1877, for example, John William Strutt, 3rd Baron Rayleigh, wrote the foundational text, The Theory Of Sound, and considered the problem. In 1909 the first U.S. patent for an "alarm device for culinary utensils" was filed, followed up regularly by similar patent claims for various valve and signaling devices. What they all missed is a level of detail the Cambridge study revealed—the swirling vortices.

"Pipes inside a building are one classic example and similar effects are seen inside damaged vehicle exhaust systems," said Ross Henrywood, the study's lead author. "Once we know where the whistle is coming from, and what's making it happen, we can potentially get rid of it."

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.

Vortex production starts as steam comes up the kettle's spout and meets a hole at the start of the whistle, which is much narrower than the spout itself. This contracts the flow of steam as it enters the whistle and creates a jet of steam passing through it. The steam jet is naturally unstable, like the jet of water from a garden hose that starts to break into droplets after it has travelled a certain distance. As a result, by the time it reaches the end of the whistle, the jet of steam is no longer a pure column, but slightly disturbed.

These instabilities cannot escape perfectly from the whistle. As they hit the second whistle wall, they form a small pressure pulse. This pulse causes the to form vortices as it exits the , and it is these vortices that produce the siren sound that has conditioned millions of people to anticipate the coming of the tea.

Explore further: How the kettle got its whistle

More information: Phys. Fluids 25, 107101 (2013); DOI: 10.1063/1.4821782

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5 / 5 (2) Nov 15, 2013
How is this different from article that you guys posted last month?


Other than the category they're classifying it as...
1 / 5 (1) Nov 16, 2013
Both supplement each other.
This one does not mention non dimensional analysis.
I can now use non dimensional analysis to disprove
the concept of dissonant and consonance in human hearing
and in theories of music. Of which I had not considered using
until YOU pointed out a second posting to tea kettle physics!
Other second postings actually do have no word-for-word difference.
My luck here.
met a more fishes
1 / 5 (3) Nov 17, 2013
to beleg,
i fail to see how either of these articles disproves the perception of consonance or its aesthetic application, i.e. if we decided middle A to be 540hz instead of 440hz, we would still perceive a "fifth" at 3/2 the frequency (810 instead of 660). I do not know what your theory posits and perhaps am not fully grasping non-dimensional analysis, but I don't believe modeling acoustic systems using variables only affects the concept of consonance.
1 / 5 (1) Nov 17, 2013
to met a more fishes
The perception of consonance was not consider in the article or research.
Drop the units of measure - frequency, distance, "fifth" and you have non-dimensional analysis.
Your standpoint stems from dimensional analysis. Concept of consonance stems from this.
You have many dimensionless variables in acoustics.

I can not tell you what you will perceive when you hear sound. You can apply what you have learned from measurement theory to convince yourself that your perceptions match those of measurement theory.

I posit non-dimensional analysis will show your perceptions lack dimensionality. The mentally impose units of measure learned are arbitrary imposed as well.

A case in point is the superposition of sound waves giving rise to perceptions (sounds) that have no physically or measurable counterpart.
met a more fishes
1 / 5 (3) Nov 17, 2013
I am not sure how we can analyze waves without taking frequency into account, even other aspects such as phase are only aspects of an oscillation with some period. I can understand studying wave systems without these aspects (ex. Standing waves) in a mechanical sense I just don't think it can be applied to the study of music. Music is a function of not just the acoustic system but also how our minds make sense of those sounds, we hear the waves but we perceive the relations between them.
1 / 5 (1) Nov 18, 2013
Your mind makes "sense" of sounds before you "hear" the "waves" and perception of the "relationships" between those waves.
The "make sense of those sounds", the "waves", the "relationships" and "perception" you have in mind are not present in the womb. Nor are these events or objects mentioned present in the form you have in mind during gestation.

You can analyze waves without taking "frequency into account" by assigning meaning to any existing sound you are able to perceive (process). This is labeled "language." And you are going to communicate with others of the same species no matter at what frequency within the threshold this takes place.

Superposition of waves give rise to a process (perception) of waves that arises from phase space. Not all parameters of phase space are physical. An oscillation and a period are an aspects of phase space. Phase space is allowed to describe all aspects of a system. Oscillations and periods are aspects of phase space and not the other way around

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