What is it about?
In turbulent flows, the energy is usually transferred forward (from large eddies towards smaller eddies). However it is known that under some constraints (imposed for example by a thin layer of fluid, or by the Coriolis force on the Earth) the energy can be transferred backwards (from small-scle eddies to large eddies). Whereas most of previous studies used a two-dimensional driving force for the flow, this study shows that using a 3D driving force can reverse the direction of the energy cascade in some cases.
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Why is it important?
Currently no general solution has been found to the Navier-Stokes equation that governs fluid turbulence. However, turbulence is omnipresent around us, for example in industrial flows, in the atmosphere, the ocean and the Earth's external kernel. Modeling these flows currently depends on very coarse empirical relationships, and having a better understanding of fundamental properties of fluid turbulence is one of the key challenges for improving these models.
Perspectives
This study is interesting in the way that it demonstrates that the driving force can have a strong influence on the properties of turbulence, and therefore that these properties are non universal. This finding adds even more to the already well-known complexity of turbulent fluids, and shows that continuing to work on fundamental properties of turbulence is more than necessary.
Basile Poujol
Ecole Normale Superieure
Read the Original
This page is a summary of: Role of the forcing dimensionality in thin-layer turbulent energy cascades, Physical Review Fluids, June 2020, American Physical Society (APS),
DOI: 10.1103/physrevfluids.5.064610.
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