Fluttering-induced flow in a closed chamber

TL;DR

This paper investigates how elastic sheet deformations induce fluid flow in a closed chamber, deriving analytical models for stability, energy transfer, and dynamic behavior depending on key dimensionless parameters.

Contribution

It introduces a coupled fluid-structure interaction model for a deforming elastic sheet in a closed chamber, analyzing stability and energy transfer mechanisms.

Findings

Growth rates and vibration frequencies for buckling modes are analytically derived.

Initial energy distribution depends on the structure-to-fluid mass ratio, favoring fluid or sheet energy.

Most energy release occurs at a predictable time related to initial conditions and growth rate.

Abstract

We study the emergence of fluid flow in a closed chamber that is driven by dynamical deformations of an elastic sheet. The sheet is compressed between the sidewalls of the chamber and partitions it into two separate parts, each of which is initially filled with an inviscid fluid. When fluid exchange is allowed between the two compartments of the chamber, the sheet becomes unstable, and its motion displaces the fluid from rest. We derive an analytical model that accounts for the coupled, two-way, fluid-sheet interaction. We show that the system depends on four dimensionless parameters: the normalized excess length of the sheet compared to the lateral dimension of the chamber, $\Delta$; the normalized vertical dimension of the chamber; the normalized initial volume difference between the two parts of the chamber, $v_{\text{du}}(0)$; and the structure-to-fluid mass ratio, $\lambda$. We investigate the dynamics at the early times of the system's evolution and then at moderate times. We obtain the growth rates and the frequency of vibrations around the second and the first buckling modes, respectively. Analytical solutions are derived for these linear stability characteristics within the limit of the small-amplitude approximation. At moderate times, we investigate how the sheet escapes from the second mode. Given the chamber's dimensions, we show that the initial energy of the sheet is mostly converted into hydrodynamic energy of the fluid if $\lambda\ll 1$, and into kinetic energy of the sheet if $\lambda\gg 1$. In both cases most of the initial energy is released at time $ t_{\text{p}}\simeq \ln[c \Delta^{1/2}/v_{\text{du}}(0)]/\sigma$, where $\sigma$ is the growth rate and $c$ is a constant.