On November 2, 2021, Naveen Pillai successfully defended his PhD dissertation, Direct Numerical Simulation of Interface-Resolved Bubbly Flows Facilitating Plasma Formation. Naveen’s committee consisted of his co-advisors, Igor A. Bolotnov & Katharina Stapelmann, and members, J. Michael Doster, Steven Shannon, Tiegang Fang, and Mark J. Kushner.

Abstract

PILLAI, NAVEEN. Direct Numerical Simulation of Interface-Resolved Bubbly Flows Facilitating Plasma Formation. (Under the direction of Dr. Igor A. Bolotnov & Dr. Katharina Stapelmann).

The ignition of plasmas in liquids has garnered a lot of attention in the past decade for applications ranging from usage in medical instrumentation to manipulation of liquid chemistry. While direct liquid ignition often requires prohibitively large electric fields to initiate breakdown, targeting streamer formation in bubbles submerged in a liquid with a higher permittivity can lower the requisite external field strength by an order of magnitude depending on the bubble shape. Thus, a Multiphysics framework was devised to transport bubble shape data from fluid dynamics simulations (specifically, Direct Numerical Simulation [DNS]) into plasma hydrodynamics simulations wherein the plasma behavior within the bubbles could be studied.

An air/liquid plasma reactor that could reliably produce ellipsoidal bubbles was designed in which air is injected through a novel orifice geometry not unlike that of a flute submerged underwater. This geometry introduces phenomena within the “flute” that are not typically brought to light in conventional orifice studies, such as transient fluctuations in the flow of air out of nozzles adjacent to nozzle from which a bubble has recently departed. After validating the bubble formation behavior seen via DNS with air flow through one nozzle, a much larger case was designed to simulate the evolution of bubbles produced out of many nozzles in the flute, which was also validated using experiments. In the latter stages of the larger case the physics of bubbles crashing into electrodes was resolved. The bubble shape data from this case was then transported through the novel Multiphysics framework to a separate code that could simulate the plasma hydrodynamics in the bubbles near the electrodes. The behavior of the plasma in those bubbles matched that seen in prior experiments, with the bulk of the plasma typically travelling on the surface of the bubbles.

The ultimate goal of this work is to set the stage for the combination of high-resolution DNS to resolve the bubble shape evolution with a concurrent investigation of streamer formation within the bubbles. This will open up many new avenues of research in the field of plasma-liquid interactions and will offer unique insight into the phenomenon of plasma-induced bubble instabilities.