Global stability analysis of axisymmetric liquid-liquid flow focusing

TL;DR

This paper investigates the stability of liquid jetting in a coflowing liquid-liquid system using numerical and experimental methods, identifying instability mechanisms and deriving a scaling law for jet diameter.

Contribution

It provides a combined numerical and experimental analysis of global stability in axisymmetric liquid-liquid flow focusing, including new insights into instability mechanisms and a predictive scaling law.

Findings

Identification of oscillatory and convective instability modes.

Reasonable agreement between numerical stability limits and experiments.

Confirmation of two predicted instability mechanisms.

Abstract

We analyze both numerically and experimentally the stability of the steady jetting tip streaming produced by focusing a liquid stream with another liquid current when they coflow through the orifice of an axisymmetric nozzle. We calculate the global eigenmodes characterizing the response of this configuration to small-amplitude perturbations. In this way, the critical conditions leading to the instability of the steady jetting tip streaming are determined. The unstable perturbations are classified according to their oscillatory character and to the region where they are originated (convective and absolute instability). We derive and explain in terms of the velocity field a simple scaling law to predict the diameter of the emitted jet. The numerical stability limits are compared with experimental results finding reasonable agreement. The experiments confirm the existence of the two instability mechanisms predicted by the global stability analysis.