Turbulence anisotropy in a bubbly vertical channel flow with topological change

Abstract

High-fidelity numerical simulations of bubble-laden, vertical channel flow in the upward configuration, where the bubbles undergo topological changes (breakup and coalescence), were performed with the purpose of exploring the effect of the surface tension on the turbulence anisotropy in the carrier phase. A qualitative analysis shows that velocity fluctuations are enhanced in the wake of large bubbles. Moreover, as shown by the velocity spectra, these structures seem to scale with bubble size and interact with those closer to the wall. Finally, a barycentric map and other indicators of turbulence anisotropy clarify that, except at the core of the channel where the largest bubbles reside, the multiphase flow cases are actually more isotropic than the single-phase flow at a matching friction Reynolds number. This unexpected behavior is attributed to a better redistribution of energy due to an enhancement of sweep events (high-speed fluid towards the wall) in the presence of large bubbles.