Scheme: Wolfson Research Merit Awards
Organisation: Coventry University
Dates: Jan 2015-Dec 2019
Summary: My research interests gravitate around turbulence under the influence of magnetic fields and rotation in geophysical and engineering problems. Turbulence lies at the heart of an immense variety of natural and industrial processes. This ubiquitous physical phenomenon leads flows to exhibit intense, erratic fluctuations over a wide range of lengthscales, making them extremely difficult to predict. Our incomplete understanding of their dynamics currently limits the development of computationally effective models and impedes progress in some of the greatest challenges in physics and engineering. In particular: how does the motion of liquid iron in the Earth core sustain the Earth's precious magnetic field ? What is the optimal design for liquid metal heat exchangers to efficiently extract heat from
nuclear fusion or from upcoming sodium reactors ?
These challenges demand a profound understanding of how turbulence is affected by the Lorentz force, which arises within conducting fluids pervaded by magnetic fields, and the Coriolis forces due to planetary rotation. Both radically alter turbulence through diffusion (magnetic, viscous) and wave propagation (Alfven and inertial waves travel along magnetic fields and rotation). Competition and interaction between these processes is not well understood because 1) direct visualisation is not possible in opaque metals 2) Laboratory Alfven waves can only be observed in extremely high magnetic fields 3) current numerical simulations cannot cope with intense rotation or magnetic fields. To tackle this problem, I am combining experiments in very high magnetic fields with numerical simulations based on a unique method that alleviates the computational costs incurred by Coriolis and Lorentz forces in view of characterising the fundamental properties of rotating and magnetohydrodynamic turbulence, and understanding its role in the extreme regimes (intense rotation and fields) of planetary cores and nuclear reactors.
I collaborate with Warwick university who operates a large turntable for the study of rapidly rotating flows, and the GHMFL in Grenoble, which is the only lab in the world to provide access to static magnetic fields over 15T, in magnets that are large enough to accommodate our experiments. Our current experiments are of three types:
- Experiments in transparent electrolytes, whose low electric conductivity is compensated by very strong magnetic field. Transparency makes extensive LASER-based flow mapping possible, which was, until now, excluded in liquid metals. This has allowed us to build a transparent flow-model of the Earth core, that reproduces the turbulent, rotating magnetoconvection that takes place there and drives the dynamics of the Earth magnetic field (collaboration with IISc Bengalore),
- Experiments in liquid metals where the Lorentz force is extremely strong, In particular we are now in the process of elucidating the competition between highly dissipative 3D states and weakly dissipative 2D states in turbulence,
- Similar experiments but where the competition between 2D and 3D states is decided by the effect of strong rotation. This dual behaviour is critical in the atmosphere for example.