Potential singularity formation of incompressible axisymmetric Euler equations with degenerate viscosity coefficients

TL;DR

This study provides numerical evidence that axisymmetric Euler equations with degenerate viscosity may develop finite-time singularities characterized by a two-scale traveling wave, driven by vortex dipoles, unlike the regularized Navier-Stokes solutions.

Contribution

The paper demonstrates the potential formation of finite-time singularities in degenerate viscosity Euler equations with detailed two-scale traveling wave behavior, supported by numerical evidence.

Findings

Potential finite-time singularity formation in degenerate viscosity Euler equations.

Two-scale traveling wave structure characterized by a collapsing ring.

Regularization by constant viscosity prevents singularity development.

Abstract

In this paper, we present strong numerical evidences that the incompressible axisymmetric Euler equations with degenerate viscosity coefficients and smooth initial data of finite energy develop a potential finite-time locally self-similar singularity at the origin. An important feature of this potential singularity is that the solution develops a two-scale traveling wave that travels towards the origin. The two-scale feature is characterized by the scaling property that the center of the traveling wave is located at a ring of radius $O((T-t)^{1/2})$ surrounding the symmetry axis while the thickness of the ring collapses at a rate $O(T-t)$. The driving mechanism for this potential singularity is due to an antisymmetric vortex dipole that generates a strong shearing layer in both the radial and axial velocity fields. Without the viscous regularization, the $3$D Euler equations develop a sharp front and some shearing instability in the far field. On the other hand, the Navier-Stokes equations with a constant viscosity coefficient regularize the two-scale solution structure and do not develop a finite-time singularity for the same initial data.