Sam Lewin

I am a non-stipendiary Junior Research Fellow here at Trinity, where I was also an undergraduate from 2014-2018. In the years since then, I was a PhD student in the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge and, subsequently, a postdoc in the Department of Mechanical Engineering at the University of California, Berkeley.

As a Hooke Fellow, I am responsible for a small amount of class teaching in the Mathematical Institute (third and fourth year courses in Applied Mathematics). Each year, I also offer a number of essay and dissertation projects in areas related to my research for senior undergraduate and master’s students. If you are interested in working with me on a project, please feel free to get in touch.

I study flows in the natural environment, with a particular interest in how their dynamics are influenced by buoyancy forces due to density variations in the fluid. We can model these flows mathematically using a combination of hydrodynamic and thermodynamic equations.

Fluids that are stratified by their density, such as the ocean, support a special type of subsurface oscillatory motion called an internal gravity wave. We know from field measurements that these waves propagate throughout the ocean interior, transporting energy and momentum over large distances and shaping both regional and global circulations. My work looks at how these waves evolve and interact with each other, fast-moving currents, and seafloor topography.

I am also interested in the dynamics of mixing, that is, what happens when the diffusion of heat and salt gradually smooths out density variations in the flow. Mixing is greatly enhanced by turbulence, which stirs the fluid around to expedite diffusion. I study the formation and evolution of turbulence, how it interacts with internal gravity waves, and how buoyancy forces modify the properties of the resulting mixing.  

S. F. Lewin, A. K. Kaminski, A. Balakrishna & M. M. P. Couchman, ‘Instability and breaking of internal waves in a horizontal shear layer’, J. Fluid Mech. 1034 (2026), A55 [https://doi.org/10.1017/jfm.2026.11456]

S. F. Lewin, A. K. Kaminski, J. M. McSweeney & A. F. Waterhouse, ‘Multiscale mixing variability on the inner shelf’, J. Phys. Oceanogr. 55(10) (2025), 1735-1750 [https://doi.org/10.1175/JPO-D-25-0012.1]

S. F. Lewin & C. P. Caulfield, ‘Stratified turbulent mixing in oscillating shear flows’, J. Fluid Mech. 934 (2022), R3 [https://doi.org/10.1017/jfm.2022.537]