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Robert Long

Postdoctoral Researcher
University of Liverpool
PhD Title
Force Balances and Dynamical Scaling of Rotating Convection in the Earth’s core
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I graduated from Coventry University with First Class BSc (Hons) Applied Mathematics and Theoretical Physics. I spent two summers performing research in Condensed Matter Physics, looking specifically into Nanophotonics. I presented this work at the 'Mathematicians of Tomorrow' conference.

During my third year, my dissertation was in the field of Geophysical Fluid Dynamics. The project involved developing a mathematical model from the full 3D Navier-Stokes governing equations, and implementing this numerically to simulate the flow.
Dissertation title - 'A Two-Dimensional Model for Oceanic and Atmospheric Flows with a Turbulent Ekman Layer'

Research Interests

Convection within Earth’s fluid core generates the planetary scale magnetic field. The underlying fluid mechanics responsible for maintaining the magnetic field are still not completely understood. Core convection occurs on a vast range of spatio-temporal scales and is complicated with many ingredients such as rotation, the spherical geometry and how the mantle extracts heat from the top of the core all having important effects. My work uses numerical simulations to investigate the fluid dynamical mechanisms of hydrodynamic (thermal) rotating convection.

Scaling behaviour of rotating convection

Rotating convection in a plane layer is known to exist in different dynamical regimes depending on the values of the control parameters. We wanted to know if we can find similar regimes in spherical shell rotating convection. To answer this we have performed a systematic parameter study varying the control parameters representing the strength of rotation (Ekman number) and buoyancy (Rayleigh number) allowing us to developing scaling laws describing the flow properties and heat transfer. By correlating the observed changes in scaling behaviour we have constructed a regime diagram in which different regimes are identified, each being governed by their own flow physics. The regime diargam is a useful tool allowing us to specifically choose parameter values for future dynamo runs to investigate the dynamics most relevant to Earth's core.
This work has been published in the Journal of Fluid Mechanics.

Boundary layers in rotating convection

The dynamics and interplay of the thermal and viscous boundary layers in convecting systems are responsible for controlling the global heat transfer and flow properties. Most studies have prescribed a fixed-temperature on the boundaries however for many astro- and geophysical applications fixed-flux thermal boundary conditions are appropriate (e.g. at the core-mantle boundary). I have been evaluating different methods for defining the thermal boundary layer thickness to find a robust definition allowing direct comparison between the different model configurations which are often used to study rotating convection.

High latitude convection in Earth’s core

The natural geometry when considering convection in Earth’s core is a rotating spherical shell. Practical considerations have led to many numerical and laboratory investigations using plane layer and cylindrical domains with the (constant value) gravity vector antiparallel to the rotation axis. This configuration is thought to be representative of convection at high latitudes. The behaviour of the heat transport (Nusselt number) and flow speeds (Reynolds number) behaves differently for spherical shell cases than the equivalent plane layer or cylindrical case. I visited Prof. Jon Aurnou at Spinlab, UCLA (Read more about Spinlab,  UCLA) and we performed a series of rotating convection experiments in a cylindrical tank using water. In these experiments we measured the heat transfer and flow speeds simultaneously. We are quantitatively comparing the results of the laboratory experiments against harvested cylindrical regions of the spherical shell models at high latitude to explicitely test if these simplified analogues are representative of the global system.

Why I chose the CDT in Fluid Dynamics

When looking at postgraduate courses, I felt that I needed a wider breadth of knowledge of the subject before I could tackle a PhD research project. Naturally, the MSc component attracted me. I am looking forward to gain exposure to experimental techniques and commercial software. A big positive for choosing the CDT is the opportunity to meet and engage with many academics before choosing the supervisory team who best suit you.