Dissipation in Onsager's critical classes and energy conservation in $BV\cap L^\infty$ with and without boundary

TL;DR

This paper investigates energy conservation in incompressible Euler equations within Onsager's critical classes, providing explicit formulas for the Duchon-Robert measure and establishing boundary energy flux conditions in Lipschitz domains.

Contribution

It introduces explicit formulas for the Duchon-Robert measure in Onsager's critical classes and proves energy conservation for BV and $L^ ablafty$ solutions, including boundary effects, extending previous results.

Findings

Explicit formulas for Duchon-Robert measure in critical classes

Energy conservation for BV and $L^ ablafty$ solutions with boundary considerations

Introduction of normal Lebesgue trace concept for boundary energy flux

Abstract

This paper is concerned with the incompressible Euler equations. In Onsager's critical classes we provide explicit formulas for the Duchon-Robert measure in terms of the regularization kernel and a family of vector-valued measures $\{\mu_z\}_z$, having some H\"older regularity with respect to the direction $z\in B_1$. Then, we prove energy conservation for $L^\infty_{x,t}\cap L^1_t BV_x$ solutions, in both the absence or presence of a physical boundary. This result generalises the previously known case of Vortex Sheets, showing that energy conservation follows from the structure of $L^\infty\cap BV$ incompressible vector fields rather than the flow having "organized singularities". The interior energy conservation features the use of Ambrosio's anisotropic optimization of the convolution kernel and it differs from the usual energy conservation arguments by heavily relying on the incompressibility of the vector field. This is the first energy conservation proof, for a given class of solutions, which fails to simultaneously apply to both compressible and incompressible models, coherently with compressible shocks having non-trivial entropy production. To run the boundary analysis we introduce a notion of "normal Lebesgue trace" for general vector fields, very reminiscent of the one for $BV$ functions. We show that having such a null normal trace is basically equivalent to have vanishing boundary energy flux. This goes beyond the previous approaches, laying down a setup which applies to every Lipschitz bounded domain. Allowing any Lipschitz boundary introduces several technicalities to the proof, with a quite geometrical/measure-theoretical flavour.