AbstractWe explore the transition from three-dimensional to two-dimensional turbulence in rotating turbulent flows. Inertial waves are thought of as the main mechanism driving physical processes in rotating turbulent flows. However, they can only exist in a limited flow regime and some steady anisotropic phenomena, such as Taylor columns, are driven by wave-free mechanisms. We identify these flow regimes and conditions under which inertial waves play no part with regards to formation of columnar structures, the promotion of anisotropy and the development of a transient turbulent flow field. A new mechanism is proposed by which columnar structures and anisotropy in general develop in rotating flows, which is based on a balance between the Coriolis force and the viscous or inertial forces operating in the flow field. These theories are validated experimentally using a setup where turbulence is forced through fluid injection/withdrawal and both 3D and quasi-2D flow structures develop. In line with the proposed mechanism, the columnar structures are found to scale as ∼ Ro−1 showing they form as a consequence of a balance between the
Coriolis force and the flow’s inertial forces. Surprisingly, in the fast-rotating limit (Ro → 0) it is found that the anisotropy of the average turbulent flow develops not because of the interactions of inertial waves but rather from an interplay between the Coriolis force and the average advection. The mechanism governing the spatial development of a transient turbulent flow field is shown to transition from being advection driven to being driven by linear inertial waves. This
transition is shown to be scale-dependent with large scale motions being more susceptible to the influence of the Coriolis force. The wave-free mechanisms identified here reveal an entirely new aspect of rotating turbulence and challenge the current paradigm that place inertial waves at the heart of its dynamics.
|Date of Award||21 Oct 2019|
|Supervisor||Alban Potherat (Supervisor) & Peter J. Thomas (Supervisor)|