Wednesday 23 Oct 2019: [Seminar] Superstructures and turbulence in Rayleigh-Benard convection
Dr Dimitar Vlaykov - University of Exeter
4th floor, Physics building 14:00-15:00
Turbulent superstructures, i.e. persistent large-scale flow structures in turbulent flows, play a crucial role in many geo- and astrophysical settings. Right above the onset of convection such flow patterns are theoretically well-understood in terms of linear and weakly nonlinear analysis. Far beyond onset, the emergence of turbulence leads to a complex behaviour in space and time and leaves many open questions. It is still largely unexplained whether turbulence supports or inhibits superstructures, for example. I shall present a recent study beginning to tackle this question in the idealised case of turbulent Rayleigh-Benard convection at high aspect ratio using direct numerical simulations. We shall consider the transfer rates of resolved kinetic energy and temperature variance between large-scale flow structures and small-scale fluctuations using a filtering formalism. We find that the small scales act primarily as a dissipation for the superstructures, in agreement with most turbulence models. However, we find that the height-dependent energy transfer rate has a complex structure with distinct bulk and boundary layer features which contribute to the driving of the superstructures. We also observe that the heat transfer between scales mainly occurs close to the thermal boundary layer. I shall briefly discuss how our observation correlate with the dynamics of convective plumes.