Interfacial flows

Interfacial flows are fluid motions involving boundaries between distinct phases, such as liquids and gases. Their dynamics couple interface shape and motion to forces including surface tension, pressure, and viscous stress.

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Young–Laplace equation: An equation relating pressure difference across a curved interface to surface tension and curvature. It describes how interface curvature creates pressure jumps that drive or resist motion.
Microfluidics: The manipulation of small volumes of fluids in channels and devices with micrometer-scale dimensions. At small scales, interfaces often dominate pressure and flow behavior.
Fluid mechanics: The study of fluids at rest and in motion, including liquids, gases, and plasmas. Interfacial flows extend fluid mechanics to boundaries between distinct phases.
Rayleigh–Plateau instability: The instability that causes a cylindrical liquid thread to break into drops under surface tension. It explains the breakup of jets and liquid filaments into droplets.
Turbulent multiphase flow: Turbulent motion involving multiple fluid phases and their interfaces. Turbulence stretches and fragments interfaces across scales that models struggle to resolve.
Capillary number: A dimensionless ratio comparing viscous forces with surface-tension forces. It predicts whether viscous stresses substantially deform an interface.
Drop breakup: The division of a liquid drop into smaller drops under deformation or instability. Breakup controls droplet sizes in sprays, emulsions, and inkjet printing.
Surface tension: The energy cost per unit area of creating a fluid interface, also expressed as force per unit length. It resists interface expansion and drives curvature-dependent forces.
Saffman–Taylor instability: An instability in which a less viscous fluid displacing a more viscous one forms branching fingers. It produces characteristic interface patterns during fluid displacement in porous media.
Coalescence: The merging of two or more drops or bubbles into a larger fluid body. Predicting when thin intervening films rupture remains challenging.