On the regularity of axially-symmetric solutions to the incompressible Navier-Stokes equations in a cylinder

W. S. Ożański, W. Zajączkowski

Published 2024-05-26Version 1

We consider the axisymmetric Navier-Stokes equations in a finite cylinder $\Omega\subset\mathbb{R}^3$. We assume that $v_r$, $v_\varphi$, $\omega_\varphi$ vanish on the lateral boundary $\partial \Omega$ of the cylinder, and that $v_z$, $\omega_\varphi$, $\partial_z v_\varphi$ vanish on the top and bottom parts of the boundary $\partial \Omega$, where we used standard cylindrical coordinates, and we denoted by $\omega =\mathrm{curl}\, v$ the vorticity field. We use estimates and $H^3$ Sobolev estimate on the modified stream function to derive three order-reduction estimates. These enable one to reduce the order of the nonlinear estimates of the equations, and help observe that the solutions to the equations is ``almost regular''. We use the order-reduction estimates to show that the solution to the equations remains regular as long as, for any $p\in (6,\infty)$, $\| v_\varphi \|_{L^\infty_t L^p_x}/\| v_\varphi \|_{L^\infty_t L^\infty_x}$ remains bounded below by a positive number.