Ever wondered why water splays when it hits the sink before heading down the plughole? This everyday household occurrence, which has baffled engineers for centuries, has finally been explained by an Indian-origin researcher at the University of Cambridge. The phenomenon, known as a hydraulic jump, was documented first by famous inventor and painter Leonardo da Vinci in 1500’s.
Hydraulic jumps are harmless in our household sinks but they can cause violent waves, turbulence and whirlpools in deeper water, said Rajesh Bhagat, a PhD student at St John’s College, the University of Cambridge in the UK. Since the 1820s scientists have believed that hydraulic jumps occur partly as a result of the gravitational pull. However, the latest study published in the Journal of Fluid Mechanics has disproved this longstanding theory. Bhagat fired jets of water upwards and sideways onto flat surfaces, and witnessed exactly the same hydraulic jumps as those when the water flowed downwards. He suspected they could all be affected by the same factors – surface tension and viscosity.
By altering these attributes of the water he was able to accurately predict the size of the hydraulic jumps. This was regardless of which direction the water was moving – debunking the 200-year-old gravitational theory as the cause of a kitchen sink type hydraulic jump. This kind of hydraulic jump is known as a circular hydraulic jump. Paul Linden, a professor at the University of Cambridge described Bhagat’s findings as ‘groundbreaking’. “His experiments and theory show that the surface tension of the liquid is the key to the process and 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,” Linden said. Bhagat predicts that his findings could have wide-reaching consequences for industries that have high levels of water consumption. “Knowing how to manipulate the boundary of a hydraulic jump is very important and now with this theory we can easily extend or reduce the boundary,” he said. “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,” said Bhagat. He hopes that the research will also be used to find new ways to help us use less water in the average household.