Little Earth Experiment:A Journey Toward the Earth's Tangent Cylinder

Abstract

This dissertation presents a theoretical contribution on the onset of rotating magneto-convection and a new experimental setup built to study the onset and the development of convection in the Earth Tangent Cylinder (TC). The theoretical contribution is a linear stability analysis of the onset of convection for an electrically conducting fluid in rotation and permeated by a magnetic field. This work highlighted the importance of the magnetic field as it enforces a specific mode of convection at onset for a certain range of parameters.The apparatus was designed to show for the first time experimentally the significant role played by the magnetic field on the flow structures and bring forward the first evidence of a polar vortex in the TC with a quantitative measurement technique such as particle image velocimetry (PIV). In order to reach these goals, the experimental setup consisted in an hemispherical dome filled with a transparent conducting fluid heated at the center, cooled on the outside and spun inside a high external magnetic field. The hemispherical dome is approximatively 30cm diameter. The fluid used is sulphuric acid at 30% mass concentration, because of its conductivity of approximatively 80S/m and its transparency, allowing both interactions with the magnetic field and visualization for PIV measurements. To compensate against the weak conductivity of sulphuric acid we used a unique 10T magnet. As a result, we were able to study the di↵erence in the convective flow between the magnetic and nonmagnetic case. It has been shown that convective structures under a magnetic field at onset become much larger leading to one o↵ axis vortex. Above onset it has also been highlighted that this structure is maintained whereas without magnetic field the flow is very di↵erent between onset and developed convection. Indeed at the onset we observe numerous structures that coalesce into one large centered structure far from the onset of convection.

Date of Award	Jul 2016
Original language	English
Awarding Institution	Coventry University
Sponsors	Leverhulme Trust
Supervisor	Alban Potherat (Supervisor) & Binod Sreenivasan (Supervisor)