Large Eddy Simulation of Microbubble Transport in Vertical Channel Flows

Large eddy simulation of microbubble dispersion and flow field modulation in vertical channel flows

“…More specifically, two‐way coupled LES predictions are compared against the DNS of Molin et al at Re τ = 150 and for d b = 110 and 220 μm in both upward and downward flow directions. To these predictions, the accuracy of which for mean fluid and bubble velocity was previously demonstrated in Asiagbe et al, additional LES‐based results are added for d b = 330 μm. In Figure , the same profiles and comparisons are shown for the mean bubble streamwise velocity.…”

“…In pipes and channels, it has been observed how small bubbles, that tend to remain spherical, concentrate near the wall in upflow and in the center of the flow in downflow . This effect has been generally attributed to the action of the lift force, which pushes the bubbles perpendicularly to the direction of the main fluid motion, and in the direction of the negative, in upflow, and positive, in downflow, fluid velocity gradient …”

“…In a liquid–gas turbulent flow, the large‐scale turbulent structures interact with the bubbles and are responsible for the macroscopic bubble motion, while small‐scale turbulent structures only captured in LES, and the less energetic small scales are approximated using a subgrid‐scale (SGS) model, coupling of bubble tracking technique and LES can in principle reproduce the large scale motion responsible for the bubble motion. In our previous works, an LES Eulerian–Lagrangian model was successfully applied to horizontal channel flows and its initial application to a vertical channel flow was investigated . In these studies, LES was demonstrated to achieve a level of detail sufficient to predict bubbly flows with accuracy.…”

“…A full‐validation of the model is provided, starting from the single‐phase flow and subsequently comparing predictions with the bubbly flow DNS‐based results of Molin et al at a shear Reynolds number Re τ = 150. With respect to our previous work, the range of microbubble diameters is extended to d b = 330 μm to provide additional details with respect to the complex mutual interactions between turbulence and the bubbles at various bubble sizes, particularly near the channel walls. Extension of the modeling approach to the higher Reynolds number Re τ = 590 was initially demonstrated elsewhere .…”

“…With respect to our previous work, the range of microbubble diameters is extended to d b = 330 μm to provide additional details with respect to the complex mutual interactions between turbulence and the bubbles at various bubble sizes, particularly near the channel walls. Extension of the modeling approach to the higher Reynolds number Re τ = 590 was initially demonstrated elsewhere . Here, the effect of higher levels of turbulence on the bubble distribution and the modifications, induced by the presence of these bubbles, to the continuous phase flow field are investigated in detail.…”