Emergence of Capillary Waves in Miscible Coflowing Fluids

Area of Science:

• Fluid Dynamics
• Interfacial Science
• Wave Phenomena

Background:

• Capillary waves are typically observed at interfaces between immiscible fluids.
• Understanding fluid interfaces is crucial for various industrial and scientific applications.

Purpose of the Study:

• To investigate the existence and behavior of capillary waves at the interface of miscible coflowing fluids.
• To develop a method for measuring transient interfacial tension in miscible systems.
• To explore the transition between different wave regimes in confined fluid flows.

Main Methods:

• Experimental observation of capillary waves in coflowing miscible fluids.
• Analysis of wave number-frequency scaling to identify different flow regimes.
• Development of a theoretical model to explain observed phenomena and measure interfacial tension.

Main Results:

• Demonstrated the existence of capillary waves at miscible fluid interfaces.
• Identified a transition from an inertial regime (k∼ω^{0}) to a capillary wave regime (k∼ω^{2/3}).
• Successfully measured effective interfacial tension and its rapid decay on millisecond timescales.

Conclusions:

• The interplay of transient interfacial stresses and confinement drives capillary wave formation in miscible fluids.
• This work provides a novel method for measuring transient interfacial tension at unprecedentedly short timescales.
• The findings extend the understanding of interfacial dynamics in miscible fluid systems.