Fluctuations and Pinch-Offs Observed in Viscous Fingering

TL;DR

This study reports new phenomena in viscous fingering within Hele-Shaw channels, including width fluctuations and pinch-off events, which depend on flow rate and are not yet explained by existing theories.

Contribution

The paper presents novel experimental observations of width fluctuations and pinch-off events in viscous fingering, expanding understanding beyond previous experiments.

Findings

Width fluctuations scale with Ca^{-0.64}

Pinch-off and reconnection events occur at higher flow rates

Fluctuations and pinch-offs are robust but unexplained by current theory

Abstract

Our experiments on viscous (Saffman-Taylor) fingering in Hele-Shaw channels reveal several phenomena that were not observed in previous experiments. At low flow rates, growing fingers undergo width fluctuations that intermittently narrow the finger as they evolve. The magnitude of these fluctuations is proportional to Ca^{-0.64}, where Ca is the capillary number, which is proportional to the finger velocity. This relation holds for all aspect ratios studied up to the onset of tip instabilities. At higher flow rates, finger pinch-off and reconnection events are observed. These events appear to be caused by an interaction between the actively growing finger and suppressed fingers at the back of the channel. Both the fluctuation and pinch-off phenomena are robust but not explained by current theory.