Direct Numerical Simulation Study of Microbubble Entrapment in Vortical Structures in a Turbulent Channel Flow*

We have performed direct numerical simulations of microbubbles in a turbulent channel flow to better understand how bubbles interact with turbulent structures. The flow is simulated using a pseudo-spectral solver, and the bubbles are modeled as massless point particles using modified Maxey-Riley equations. The flow is driven by a constant pressure gradient with no gravity in order to determine if bubbles are preferentially drawn to hairpin vortices found in turbulent wall-bounded flows. Hairpin vortex locations—identified by the λ-2 criterion—are correlated with bubble locations to show the capturing capabilities by different portions of these structures. We explore the statistics of bubble residence times and examine its dependence of the vortex Reynolds number, distance from the wall, and other flow parameters. This is an extension of a previous work which examined bubble entrapment in a Lamb-Oseen vortex (Kelly et al.  Phys. Fluids 33 (6), 061702, 2021); we now seek to understand the nature of temporary, selective entrapment in more complex flows.