Long, Robert Stephen (2020) Regimes and scaling laws for convection with and without rotation. Integrated PhD and Master thesis, University of Leeds.
Abstract
The geodynamo is maintained by turbulent rotating convection in Earth's liquid iron outer core. Core dynamics are inaccessible to direct measurement and our understanding comes from a combination of observations, theoretical arguments, laboratory experiments and numerical simulations. The vast range of spatial and temporal scales present prevent numerical or physical experiments from being able to reproduce the convective state of Earth's core exactly. This motivates systematic studies in which we attempt to understand the fundamentals of convection over the broad range of accessible parameter space with a view to identifying asymptotic behaviour; if such behaviour is found, then this could allow extrapolation to Earth's core values. We present a combined numerical-laboratory survey of hydrodynamic convection to elucidate the role of different boundary conditions, geometries and the influence of rotation over a wide range of parameter space. We focus on transitions in thermal convection with a particular interest in the constraining effects of rotation. The transition from rapidly rotating to weakly rotating convection is hypothesised to be controlled by the thermal boundary layers. Using plane-layer Rayleigh-Benard convection simulations we determine a robust definition of the thermal boundary layer which can be used for non-rotating or rotating convection with different thermal boundary conditions. Different physical regimes of convection are identified in a rotating spherical shell by correlating changes in both local and global flow diagnostics. We identify a regime of quasi-geostrophic turbulence which may be relevant to describing the dynamics of Earth's core. Laboratory experiments and local plane-layer simulations are thought to be analogues for convection in the polar region of a spherical shell and unsurprisingly these modelling approaches do not agree with full spherical shell calculations. In an attempt to unify these different modelling approaches we harvest a fluid region at high latitude and are able to explicitly show good agreement between experiments and local simulations with polar convection. Ultimately this work provides a platform to investigate convection in a regime which bridges that of Earth's core.
Metadata
Supervisors: | Mound, Jon and Davies, Chris and Tobias, Steven |
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Awarding institution: | University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering (Leeds) > School of Computing (Leeds) |
Academic unit: | EPSRC Centre for Doctoral Training in Fluid Dynamics |
Identification Number/EthosID: | uk.bl.ethos.826759 |
Depositing User: | Mr Robert Long |
Date Deposited: | 09 Apr 2021 12:42 |
Last Modified: | 11 May 2021 09:53 |
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