Marangoni shocks in unobstructed soap-film flows

TL;DR

This paper experimentally demonstrates the existence of Marangoni shocks in steady soap-film flows, revealing abrupt velocity drops linked to film elasticity, which may influence understanding of two-dimensional turbulence.

Contribution

It provides the first experimental evidence of Marangoni shocks in soap films and connects these shocks to turbulence mechanisms.

Findings

Velocity peaks and drops observed experimentally.

Marangoni shocks identified as causes of velocity discontinuities.

Turbulent fluctuations intensified near shocks.

Abstract

It is widely thought that in steady, gravity-driven, unobstructed soap-film flows, the velocity increases monotonically downstream. Here we show experimentally that the velocity increases, peaks, drops abruptly, then lessens gradually downstream. We argue theoretically and verify experimentally that the abrupt drop in velocity corresponds to a Marangoni shock, a type of shock related to the elasticity of the film. Marangoni shocks induce locally intense turbulent fluctuations and may help elucidate the mechanisms that produce two-dimensional turbulence away from boundaries.