Anomalous dissipation in fluids, deterministic turbulence, and intermittency

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ShvydkoyDMS-1210896 The most pressing mathematical issues arising in fluid dynamics are becoming increasingly intertwined with the statistical theory of turbulence. The Navier-Stokes and Euler equations have served as the primary tools for numerical modelling, yet the very basic question of whether they can actually produce solutions satisfying laws of turbulence has not been settled. In recent years, with the advances of topological methods and better understanding of the nonlinear structure of the equations, this problem, commonly known as the Onsager conjecture, has come within our reach. The underlying theme of this project is to develop an analytical approach for studying statistical properties of deterministic solutions. The focus is on finding stationary energy dissipative weak solutions of the Euler and active scalar equations in the Onsager-critical regularity class, developing rigorous fractal analysis of the empirical concept of intermittency as a volumetric measure of non-uniformity of the Richardson cascade, excluding extreme deviations from the classical Kolmogorov laws as shown by the vast experimental data, and establishing links between intermittency and the global regularity problem. Turbulence is a complex chaotic process of fluid motion that commonly happens when a stirring force, like heat from the sun or an airplane cutting fast through air, injects a lot of energy into the system. This motion gets so complicated and rough that a part of the kinetic energy gets lost, creating what is known as anomalous dissipation. In our lives we can see this dissipation responsible, for example, for creation of additional drag in the turbulent wake of an airplane or our cars. In order to improve energy efficiency it is therefore essential to understand the mechanisms behind the process of anomalous energy loss and the reasons why it arises. In this project the investigator develops mathematical foundations of this aspect of turbulence based directly on the governing equations of fluid motion. A particular emphasis is given to studying non-uniformity of energy dissipation, which allows identifying regions where it occurs the most. An integral part of the project is developing the analytical and computational skills of graduate and undergraduate students.