Global stability analysis of axisymmetric liquid-liquid flow focusing

We analyse 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 originate (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.

Automated summary

In this study, the stability of steady jetting tip streaming generated by focusing liquid streams through an axisymmetric nozzle was analyzed using numerical and experimental methods. The critical conditions leading to instability and the classification of unstable perturbations were determined. Experimental results were compared with numerical stability limits, showing reasonable agreement and confirming the predicted instability mechanisms.