Periodic Reporting for period 3 - FLAVE (Energetics of natural turbulent flows: the impact of waves and radiation.)
Okres sprawozdawczy: 2021-03-01 do 2022-08-31
The project aims at characterizing the energy transfers in some turbulent flows of geophysical, astrophysical and climatological relevance. Turbulence remains unresolved in coarse models of stellar evolution, planetary evolution or climate dynamics. We perform targeted experimental and numerical studies aimed at uncovering the 'constitutive laws' that characterize the behavior of such turbulent flows. These constitutive laws are key to developing physically based parameterizations of turbulent transport to be implemented in coarse models climatological or astrophysical models. The project focuses on three main directions of research:
1) The two-way interaction of surface waves with subsurface mean flows is key to understanding transport and mixing near the ocean surface.
2) Rapidly rotating natural flows can be described to some extent using simple two-dimensional models. However, to better reproduce the behavior of natural flows these models should include the interaction between the quasi-2D flow and waves, and with density stratification. Stably stratified rapidly rotating flows are the canonical situation of oceanic and atmospheric turbulence. The project aims at describing the transport propertied of these flows, and the additional dissipation due to the emergence of wave dynamics.
3) Convection is a key mechanism for vertical mixing in the atmosphere and the ocean mixed layer. However, laboratory setups of turbulent convection are strongly influenced by the boundaries of the experimental tank. The project aims at designing an innovative experimental setup where convection is driven directly in the bulk of the flow through the absorption of visible light, thus bypassing the influence of the boundaries. The resulting convective turbulence would much better reproduce the regimes of geophysical and astrophysical relevance.
1) The two-way interaction of surface waves with subsurface mean flows is key to understanding transport and mixing near the ocean surface.
2) Rapidly rotating natural flows can be described to some extent using simple two-dimensional models. However, to better reproduce the behavior of natural flows these models should include the interaction between the quasi-2D flow and waves, and with density stratification. Stably stratified rapidly rotating flows are the canonical situation of oceanic and atmospheric turbulence. The project aims at describing the transport propertied of these flows, and the additional dissipation due to the emergence of wave dynamics.
3) Convection is a key mechanism for vertical mixing in the atmosphere and the ocean mixed layer. However, laboratory setups of turbulent convection are strongly influenced by the boundaries of the experimental tank. The project aims at designing an innovative experimental setup where convection is driven directly in the bulk of the flow through the absorption of visible light, thus bypassing the influence of the boundaries. The resulting convective turbulence would much better reproduce the regimes of geophysical and astrophysical relevance.
We have studied the behavior of waves propagating at the surface of the ocean, including planetary rotation. We have discovered that the resulting mean flow is unstable. This instability, coined the Edman-Stokes instability, leads to chaos and turbulence near the ocean surface, with important consequences for the transport and mixing properties of the flow. The resulting turbulent flow is currently under investigation.
We have leveraged the capabilities of modern Graphics Processing Units to study the behavior of rapidly rotating flows, when these flows are close to two-dimensional. This approach has allowed us to investigate these turbulent flows in extreme parameter regimes, beyond state-of-the-art 3D Direct Numerical Simulations and laboratory experiments. In collaboration with physical oceanographers, we then studied similar quasi-2D models that include both rapid rotation and density stratification, with applications to the theoretical modelization of climate dynamics. Based on the intuition gathered during the project, we derived a quantiative theory that can be used as a parameterization in idealized models of oceans and planetary atmospheres.
In the laboratory, we have successfully developed a radiatively driven convection experiment. The experimental apparatus indeed leads to regimes of thermal convection of relevance to astrophysical systems, thus bridging an important gap between laboratory experimentation and astrophysical modelling. In parallel, we have modelled the experimental apparatus using state-of-the-art numerical methods. After satisfactory cross-validation between the experimental and numerical results, we used the numerical approach to characterize the behavior of the system beyond the sole parameter regimes accessible in the laboratory.
We have leveraged the capabilities of modern Graphics Processing Units to study the behavior of rapidly rotating flows, when these flows are close to two-dimensional. This approach has allowed us to investigate these turbulent flows in extreme parameter regimes, beyond state-of-the-art 3D Direct Numerical Simulations and laboratory experiments. In collaboration with physical oceanographers, we then studied similar quasi-2D models that include both rapid rotation and density stratification, with applications to the theoretical modelization of climate dynamics. Based on the intuition gathered during the project, we derived a quantiative theory that can be used as a parameterization in idealized models of oceans and planetary atmospheres.
In the laboratory, we have successfully developed a radiatively driven convection experiment. The experimental apparatus indeed leads to regimes of thermal convection of relevance to astrophysical systems, thus bridging an important gap between laboratory experimentation and astrophysical modelling. In parallel, we have modelled the experimental apparatus using state-of-the-art numerical methods. After satisfactory cross-validation between the experimental and numerical results, we used the numerical approach to characterize the behavior of the system beyond the sole parameter regimes accessible in the laboratory.
The capabilities of Graphics Processing Units allow us to run idealized models in extreme parameter regimes, thus deriving physically based parameterization for fully turbulent flows. We plan to gradually include additional physical ingredients of natural flows, to obtain a parameterization that has skill beyond these idealized models, all the way to the real situation of an ocean or planetary atmosphere.
The experimental apparatus also opens an avenue for the study of fully turbulent regimes of thermal convection, of relevance to the modelling of geophysical and astrophysical flows. Here again, the experimental apparatus offers some flexibility to add external physical ingredients and characterize their impact on the transport properties of the flow.
The experimental apparatus also opens an avenue for the study of fully turbulent regimes of thermal convection, of relevance to the modelling of geophysical and astrophysical flows. Here again, the experimental apparatus offers some flexibility to add external physical ingredients and characterize their impact on the transport properties of the flow.