Turbulence modulation in buoyancy-driven bubbly flows

TL;DR

This DNS study investigates how buoyancy-driven bubbles influence turbulence, revealing changes in bubble trajectories, velocities, and flow energy spectra, aligning with experimental observations of turbulence modulation.

Contribution

The paper provides a detailed DNS analysis of turbulence modulation by buoyant bubbles, highlighting scale-dependent energy spectra and bubble dynamics in turbulent flows.

Findings

Bubble trajectories become more curved with increased turbulence.

Average bubble rise velocity decreases as turbulence intensifies.

Flow energy spectrum exhibits pseudo-turbulence and Kolmogorov scaling depending on scale.

Abstract

We present a Direct Numerical Simulation (DNS) study of buoyancy-driven bubbly flows in the presence of large scale driving that generates turbulence. On increasing the turbulence intensity: (a) the bubble trajectories become more curved, and (b) the average rise velocity of the bubbles decreases. We find that the energy spectrum of the flow shows a pseudo-turbulence scaling for length scales smaller than the bubble diameter and a Kolmogorov scaling for scales larger than the bubble diameter. We conduct a scale-by-scale energy budget analysis to understand the scaling behaviour observed in the spectrum. Although our bubbles are weakly buoyant, the statistical properties of our DNS are consistent with the experiments that investigate turbulence modulation by air bubbles in water.