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Optimal minimax formula for bounds on ensemble averages of statistically stationary three-dimensional Navier-Stokes flows
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Optimal minimax formula for bounds on ensemble averages of statistically stationary three-dimensional Navier-Stokes flows

Anne Bronzi, Cecília F Mondaini and Ricardo M. S Rosa
ArXiv.org
11 Jun 2026
url
https://doi.org/10.48550/arXiv.2606.12825View
Preprint (Author's original) Open arXiv.org - Non-exclusive license to distribute

Abstract

Mathematics - Analysis of PDEs Mathematics - Mathematical Physics Physics - Mathematical Physics
We establish an optimal upper bound formula for ensemble averages of flow quantities associated with the three-dimensional incompressible Navier-Stokes equations. The formula takes the form of a minimax problem, extending the framework developed by Tobasco, Goluskin, and Doering (2018) for finite-dimensional systems and by Rosa and Temam (2022) for the two-dimensional Navier-Stokes equations. The lack of global well-posedness for the 3D case presents a significant challenge, which we overcome by working within the space of Foias-Prodi stationary statistical solutions. The minimax formula is derived by exploiting suitable compactness and continuity properties of specific subspaces of probability measures under the weak topology of the phase space. A distinguishing feature of our result is the characterization of the maximizing measures: unlike the previous cases, the optimal bounds in 3D are achieved on extreme points that are specific convex combinations of at most two Dirac delta measures, instead of exactly one, a structure that naturally appears from the constraints given by the mean energy dissipation inequalities in the characterization of the Foias-Prodi stationary statistical solutions.

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