Turbulence, pseudo-turbulence, and local flow topology in dispersed bubbly flow

Abstract

Bubbly turbulent flow in a channel is investigated using interface-resolved direct numerical simulation. An efficient coupled level-set volume-of-fluid solver based on a fast Fourier transform algorithm is implemented to enable a high resolution and fast computation at the same time. Up to 384 bubbles are seeded in the turbulent channel flow corresponding to 5.4% gas volume fraction. Bubbles are clustered in the channel center due to the downward flow direction. The bubbles induce additional pseudo-turbulence in the channel center and are also able to attenuate the energy in the boundary layer by reducing the shear production. Turbulent kinetic energy budget indicates a significant buoyancy production in the channel center. A local equilibrium between buoyancy production and dissipation is observed here besides the shear production peak in the boundary layer. Comparing the local production and dissipation indicates a coexistence of boundary layer turbulence near the wall and bubble-induced pseudo-turbulence in the channel center. The liquid phase and gas phase are coupled through the complex liquid–gas interface. Local flow topology analysis is depicted in the liquid phase around the bubbles as well as in the gas phase. The flow topology of the liquid phase and the gas phase differs from each other significantly. Local dissipation is more dominant in the liquid phase near the bubble interface, whereas local enstrophy is preferred in the gas phase. In the liquid phase, a high dissipation event is preferred close to the interface, whereas a high enstrophy event is dominant away from the interface.

Numerical study of bubbly flow in a swirl atomizer

“…In addition, the bubbles are observed to migrate towards the center of the pipe thus forming a nearly gas free wall layer. Such behavior is consistent with previous research on downflow in a vertical channel [41][42][43] . Near the pipe center, the bubbles start to deform and agglomerate.…”

Structure and dynamics of small-scale turbulence in vaporizing two-phase flows

“…On another note, the statistics presented in the current analysis, are obtained by conditioning on the distance from the two-phase interface. Similar approaches were adopted in several previous analyses 12 , 50 . However, the present investigation provides more details on the dynamics of the turbulence-scalar interaction in the context of a two-phase flow, through the introduction of the non-normal effect statistics in the aforementioned fashion, which is, to the best of the authors’ knowledge, have not been considered before.…”

Enforcing accurate volume conservation in VOF‐based long‐term simulations of turbulent bubble‐laden flows on coarse grids

“…Since experimental techniques such as non‐intrusive imaging are usually limited to very dilute void fractions, 1,2 numerical investigations play a major role in improving the fundamental understanding of such flows. The increase in computational resources has allowed first large‐scale direct numerical simulations (DNS) of turbulent bubble‐laden channel flows 3–8 . While the pioneering studies of Lu and Tryggvason 9–11 featured relatively small‐scale channel flows with up to 72 bubbles, recently developed massively parallel solvers 5,12 are able to perform DNS with up to bubbles in full‐scale channels, while maintaining excellent scalability.…”

“…The increase in computational resources has allowed first large-scale direct numerical simulations (DNS) of turbulent bubble-laden channel flows. [3][4][5][6][7][8] While the pioneering studies of Lu and Tryggvason [9][10][11] featured relatively small-scale channel flows with up to 72 bubbles, recently developed massively parallel solvers 5,12 are able to perform DNS with up to  (10 4 ) bubbles in full-scale channels, while maintaining excellent scalability. However, due to the computational cost, DNS will remain limited to reduced-complexity bubbly flows at moderate Reynolds numbers for the foreseeable future.…”