"This work represents a remarkable achievement in our understanding of the dynamics of thin layers of fluid”

Since the 1820s scientists have believed that hydraulic jumps occur partly as a result of the gravitational pull. But a paper published in the Journal of Fluid Mechanics has disproved this longstanding theory.

Rajesh Bhagat, a Chemical Engineering PhD student at St John’s College, University of Cambridge, and first author of the paper, fired jets of water upwards and sideways onto flat surfaces, and witnessed exactly the same hydraulic jumps as those when the water flowed downwards.

But what was causing it? Bhagat suspected they could all 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, 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.

Professor Paul Linden, Director of Research at the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge and an author of the paper, described Bhagat’s findings as ‘ground breaking’.

He explained: “His 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."