Reverse undercompressive shock structures in driven thin film flow

TL;DR

This paper presents experimental evidence of a novel shock structure in driven thin film flows, revealing stability differences and the influence of film thickness on wave separation.

Contribution

It introduces the first experimental observation of reverse undercompressive shocks in thin films driven by surface tension gradients.

Findings

Reverse undercompressive shock is unstable to transverse perturbations.

Leading undercompressive shock is stable.

Film thickness determines wave separation phenomena.

Abstract

We show experimental evidence of a new structure involving an undercompressive and reverse undercompressive shock for draining films driven by a surface tension gradient against gravity. The reverse undercompressive shock is unstable to transverse perturbations while the leading undercompressive shock is stable. Depending on the pinch-off film thickness, as controlled by the meniscus, either a trailing rarefaction wave or a compressive shock separates from the reverse undercompressive shock.