James Friend, PhD, Washington University in St. Louis

Abstract: Turbulent multiphase flows are central to fuel injection, sprays, materials processing, and microfluidics, yet they remain difficult to design because their dynamics span coherent waves, nonlinear interactions, intermittency, rupture, and droplet formation. In this seminar, I will describe an experimental program that uses high-frequency acoustic actuation and compact MEMS-scale platforms to make these transitions observable, controllable, and ultimately predictable.

I will begin with capillary-wave turbulence measured using high-speed digital holographic microscopy, then follow the progression from driven interfacial waves to liquid-jet breakup and fuel-film atomization. These experiments motivate a different route to engineering complex flows: rather than reconstructing every microscopic field, we seek low-dimensional, dimensionless relationships connecting acoustic forcing, fluid inertia, gas coupling, and geometry to design outcomes such as droplet size, distribution width, and throughput. I will discuss how automated symbolic discovery, uncertainty quantification, and targeted experiments can identify where such relationships hold—and where a model should abstain.

I will close by showing how the same acoustic toolkit controls transport in nanoslits, porous materials, droplet deposition, and biomedical devices, illustrating a broader theme: MEMS can serve not only as useful devices, but also as precision laboratories for discovering physical laws.