When you open the tap, the stream of water that hits the sink creates a very thin, fast-flowing, circular layer of water surrounded by a thicker, concentric ring of turbulent water.
A hydraulic jump is an abrupt change in the level of a liquid that occurs when a fast-moving stream encounters a slower body of liquid and has intrigued many scientific minds. One of those minds belonged to Leonardo da Vinci.
The “jump” can be observed in everyday mechanics like tap water hitting the sink.
When you open the tap, the stream of water that hits the sink creates a very thin, fast-flowing, circular layer of water surrounded by a thicker, concentric ring of turbulent water.
That change, where the water transforms from a thin layer to a thick one is what is referred to as a hydraulic jump.
In the 16th century, Leonardo da Vinci observed and tried to decode this phenomenon, and in 1819, Giorgio Bidone, the Italian mathematician suggested that gravity played a significant part in it.
But now, researchers at the University of Cambridge have now proven that gravity plays no role in the circular hydraulic jumps of thin liquid films.
To prove this, researchers fired jets of water in various directions— downwards, upwards, and sideways—all onto flat surfaces. What they observed was that the radius of the hydraulic jump remained the same in all cases.
The researchers tried this with the same fluid and with the same flow rate alternating between different sets of observation.
The research was led by Indian origin researcher, Rajesh Bhagat, a chemical engineering PhD student at the University of Cambridge.
“If the hydraulic jump happens due to gravity, then when you change the orientation of the surface, you should see a completely different shape,” said Rajesh Bhagat, to The Chemical Engineer, a publication. “This experiment unequivocally disproves the previous gravity-based theories,” he added.
So what is the answer to this regular yet perplexing occurrence?
To understand this, the team used liquids varying in surface tension and viscosity.
They found that lowering the surface tension increases the radius of the jump while increasing the viscosity reduces the radius. The experiment concluded that gravity plays no role in the hydraulic jump, and proved that only surface tension and viscosity are the main factors behind it.
Paul Linden, director of research at the department of applied mathematics and theoretical physics and an author of the paper, said to the publication, “Bhagat’s experiments and theory show that the surface tension of the liquid is the key to the process and has this has never before been recognised even though the problem was discussed by da Vinci and many others since. This work represents a remarkable achievement in our understanding of the dynamics of thin layers of fluid.”
Talking about the use of the new found answer, Bhagat told India Today that “Understanding this process has big implications and could reduce industrial water use dramatically. People can use this theory to find new ways to clean everything from cars to factory equipment.”
It is indeed incredible that observing such a commonplace occurrence can inspire researchers to apply the answer to benefit various technologies that use water.
(Edited by Gayatri Mishra)
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