Mathematically established chaos in fluid dynamics: recurrent patterns forecast statistics

Abstract

We analyse in the Taylor-Couette system, a canonical flow that has been studied extensively for over a century, a parameter regime exhibiting dynamics that can be approximated by a simple discrete map. The map has exceptionally neat mathematical properties, allowing to prove its chaotic nature as well as the existence of infinitely many unstable periodic orbits. Remarkably, the fluid system and the discrete map share a common catalog of unstable periodic solutions with the tent map, a clear indication of topological conjugacy. A sufficient number of these solutions enables the construction of a conjugacy homeomorphism, which can be used to predict the probability density function of direct numerical simulations. These results rekindle Hopf's aspiration of elucidating turbulence through the study of recurrent patterns.