MechE Colloquium: On the effects of topography in rapidly rotating fluids: Experiments on the spin-up of a fluid in a straight cylinder with bottom topography
Deep seated planetary fluid envelops, such as metallic cores or subsurface oceans, play a fundamental role in the orbital evolution of the celestial objects via transfer of angular momentum and energy dissipation, and the generation of a magnetic field or mixing of chemical species. From a dynamical stand point these buried fluid envelops are rapidly rotating, stably, neutrally or unstably stratified regions enclosed in a solid shell. The interest in their dynamics dates back from the end of the 19th century when scientists proposed to probe internal structures of planets and moons by monitoring their rotation, initiating research on how the presence of fluid layers can reflect in their rotational dynamics. They first considered the hydrodynamics of rapidly rotating spherical shells, then spheroidal shells and more recently tri-axial ellipsoids. Meanwhile, we have geodynamical arguments and seismic observations suggesting that the Earth's Core-Mantle boundary (CMB) may not be a smooth surface but exhibit topographic features of various height and wavelengths, which have not been considered so far.
In this presentation, I will briefly introduce the geophysical context and explain why the abundant results on the topic in oceanography and atmospheric sciences may not apply to those deep fluid layers. I will then present the results from a dedicated experimental study of the Spinup of a rapidly rotating fluid in a straight cylinder with chessboard-like topography at the bottom as a proxy to address topography driven energy dissipation. I will show the particular role played by inertial waves to radiate the energy away from the topography, and shape the internal flows. I will conclude by presenting ongoing and future theoretical, numerical and experimental investigations to gain further insights.
Jerome Noir's interests focus on rotating hydro and magneto-hydro dynamics of planet’s and moon's fluid layers such as metallic cores and subsurface oceans. His research combine numerical simulations and laboratory experiments to understand how these fluid envelops contribute to the dissipation of energy, transfer of angular momentum and magnetic field generation. As part of his experimental activities, Jerome Noir is developing unique rapidly rotating apparatus and 2D/3D ultrasonic acoustic measurement systems for velocimetry in harsh environments and opaque fluids dedicated to the extreme magneto-rotational dynamics.
Jerome Noir got his PhD in 2000 from the University of Grenoble on the "Earth’s core dynamics induced by precession”, he then held a research associate position at UCLA from 2001 to 2010 before joining ETH Zürich as the head of the experimental laboratory of geophysical fluid dynamics in the Earth’s science department and study advisor of the geophysics Master. He is currently involved in a multidisciplinary Simons foundation project on "Fundamental Fluid Processes in Climate, Stellar and Planetary Modelling.
- General public