Paul Linden
University of Cambridge
Seminar Information
Engineering Building Unit 2 (EBU2)
Room 479
Seminar Recording Available: Please contact seminar coordinator, Jake Blair at (j1blair@ucsd.edu)
It is a common experience that when you turn on a tap the impact of the falling jet is to create a circular thin region of fast flowing water in the sink surrounded by a deeper region. The change in depth is abrupt at a fixed radius and is known as the circular hydraulic jump, and was first documented by Leonardo da Vinci in the late 15th century. In the supercritical region beneath the point of jet impact and the jump the flow is fast and the liquid layer is thin, so that the shear stress on the surface is large, while its speed decreases dramatically and the depth increases in the subcritical region outside the jump. This has obvious implications for using liquid jets for cleaning and decontaminating surfaces, as well as for erosion. The circular jump has been a subject of modern scientific study since Lord Rayleigh’s experiments in 1914 and, as he implied, it has been commonly assumed that gravity plays a major dynamical role in the formation of the jump. I will show simple experiments that challenge this view at the scale of the kitchen sink and explain why the role of surface tension has been ignored. Finally, I will develop a theoretical approach that delineates the role of surface tension and gravity in the jump dynamics.
I graduated with a PhD in the Department of Applied Mathematics and Theoretical Physics (DAMTP) in 1972 and remained there first as a postdoc and then on the faculty as the Director of the fluid dynamics laboratory, now the G.K. Batchelor Laboratory, until 1998. I then went as the Blasker Professor of Environmental Science and Engineering to the Department of Mechanical and Aerospace Engineering at UC San Diego. I was department chair there (2004-2009), and returned to DAMTP as the G.I. Taylor Professor of Fluid Mechanics in 2010. I am currently an Emeritus Professor in DAMTP.
My research is concerned with fluid flow in the environment and in industry. I use laboratory experiments and theoretical models to elucidate the relevant physical processes underlying these flows and to provide predictions of their properties that can be applied in practice. My current research interests are mainly on stratified turbulence and buoyancy-driven flows with applications to oceanography and flows in the built environment. At the moment my particular focus is on mixing processes in stratified shear flows and ventilation flows, and I also have an interest in hydraulic jumps in thin-film flows.