The Onset of Thermalisation in Finite-Dimensional Equations of Hydrodynamics: Insights from the Burgers Equation

Abstract

Solutions to finite-dimensional (all spatial Fourier modes set to zero beyond a finite wavenumber $K_G$), inviscid equations of hydrodynamics at long times are known to be at variance with those obtained for the original infinite dimensional partial differential equations or their viscous counterparts. Surprisingly, the solutions to such Galerkin-truncated equations develop sharp localised structures, called {\it tygers} [Ray, et al., Phys. Rev. E {\bf 84}, 016301 (2011)], which eventually lead to completely thermalised states associated with an equipartition energy spectrum. We now obtain, by using the analytically tractable Burgers equation, precise estimates, theoretically and via direct numerical simulations, of the time ${\tau }_c$ at which thermalisation is triggered and show that $τ_c \sim \kg^ξ$, with $\xi =-4/9$. Our results have several implications including for the analyticity strip method to numerically obtain evidence for or against blow-ups of the three-dimensional incompressible Euler equations.

Minor corrections to the previous version

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Cited by in corpus (5)

• Insights from a pseudospectral study of a potentially singular solution of the three-dimensional axisymmetric incompressible Euler equation
• On the thermalization of the three-dimensional, incompressible, Galerkin-truncated Euler equation
• Eye of the Tyger: early-time resonances and singularities in the inviscid Burgers equation
• Poles, Shocks and Tygers: The Time-reversible Burgers equation
• Random initial data and average shock time in the Fermi-Pasta-Ulam-Tsingou chain