On Stability and Instability of Gravity Driven Navier-Stokes-Korteweg Model in Two Dimensions

TL;DR

This paper proves that sufficient capillarity can stabilize the Rayleigh-Taylor instability in a 2D incompressible Navier-Stokes-Korteweg model, providing explicit thresholds and demonstrating the limits of capillarity's stabilizing effect.

Contribution

It extends linear stability results to the nonlinear regime and derives explicit capillarity thresholds for stability in a 2D setting.

Findings

Capillarity can inhibit RT instability when above a certain threshold.

Explicit formula for the critical capillarity coefficient in the linear RT profile case.

Capillarity cannot prevent instability if its strength is below the threshold.

Abstract

Bresch-Desjardins-Gisclon-Sart have derived that the capillarity can slow {down} the growth rate of Rayleigh-Taylor (RT) instability in the capillary fluids based on the linearized two-dimensional (2D) Navier-Stokes-Korteweg equations in 2008. Motivated by their linear theory, we further investigate the nonlinear RT problem for the 2D incompressible case in a horizontally periodic slab domain with Navier boundary condition, and rigorously verify that the RT instability can be inhibited by capillarity under our 2D setting. More precisely, if the RT density profile $\bar{\rho}$ satisfies an additional stabilizing condition, then there is a threshold $\kappa_{C}$ of capillarity coefficient, such that if the capillarity coefficient $\kappa$ is bigger than $\kappa_{C}$, then the small perturbation solution around the RT equilibrium state is \emph{algebraically} stable in time. In particular, if the RT density profile is linear, then the threshold $\kappa_{C}$ can be given by the formula $\kappa_{C}=g /(\pi^2h^{-2}+L^{-2})\bar{\rho}'$, where $2\pi L$ denotes the length of a periodic cell of the slab domain in the horizontal direction, and $h$ the height of the slab domain. In addition, we also provide a nonlinear instability result for $\kappa\in[0,\kappa_{C})$. The instability result presents that the capillarity can not inhibit the RT instability, if its strength is too small.