Formation of shocks for 2D isentropic compressible Euler

TL;DR

This paper provides an elementary constructive proof of shock formation in 2D isentropic compressible Euler equations with finite energy initial data, explicitly characterizing blowup time, location, and solution regularity, including vorticity effects.

Contribution

It introduces a new constructive method to prove shock formation with nontrivial vorticity, explicitly computing blowup parameters and handling azimuthal wave dynamics.

Findings

Shock forms in finite time from smooth initial data.

Blowup time and location are explicitly computed.

Solutions at blowup are cusp-type with Hölder 1/3 regularity.

Abstract

We consider the 2D isentropic compressible Euler equations, with pressure law $p(\rho) = (\sfrac{1}{\gamma}) \rho^\gamma$, with $\gamma >1$. We provide an elementary constructive proof of shock formation from smooth initial datum of finite energy, with no vacuum regions, and with {nontrivial vorticity}. We prove that for initial data which has minimum slope $- {\sfrac{1}{ \eps}}$, for $ \eps>0$ taken sufficiently small relative to the $\OO(1)$ amplitude, there exist smooth solutions to the Euler equations which form a shock in time $\OO(\eps)$. The blowup time and location can be explicitly computed and solutions at the blowup time are of cusp-type, with H\"{o}lder $C^ {\sfrac{1}{3}}$ regularity. Our objective is the construction of solutions with inherent $\OO(1)$ vorticity at the shock. As such, rather than perturbing from an irrotational regime, we instead construct solutions with dynamics dominated by purely azimuthal wave motion. We consider homogenous solutions to the Euler equations and use Riemann-type variables to obtain a system of forced transport equations. Using a transformation to modulated self-similar variables and pointwise estimates for the ensuing system of transport equations, we show the global stability, in self-similar time, of a smooth blowup profile.