Numerical simulation of bubble dispersion in turbulent Taylor-Couette flow

Abstract

We investigate bubble dispersion in turbulent Taylor-Couette flow. The aim of this study is to describe the main mechanisms yielding preferential bubble accumulation in near-wall structures of the flow. We first proceed to direct numerical simulation of Taylor-Couette flows for three different geometrical configurations (three radius ratios η = R 1 /R 2 : η = 0.5, η = 0.72, and η = 0.91 with the outer cylinder at rest) and Reynolds numbers corresponding to turbulent regime ranging from 3000 to 8000. The statistics of the flow are discussed using two different averaging procedures that permit to characterize the mean azimuthal velocity, the Taylor vortices contribution and the small-scale turbulent fluctuations. The simulations are compared and validated with experimental and numerical data from literature. The second part of this study is devoted to bubble dispersion. Bubble accumulation is analyzed by comparing the dispersion obtained with the full turbulent flow field to bubble dispersion occurring at lower Reynolds numbers in previous works. Several patterns of preferential accumulation of bubbles have been observed depending on bubble size and the effect of gravity. For the smaller size considered, bubbles disperse homogeneously throughout the gap, while for the larger size they accumulate along the inner wall for the large gap width (η = 0.5). Varying the intensity of buoyancy yields complex evolution of the bubble spatial distribution. For low gravity effect, bubble entrapment is strong leading to accumulation along the inner wall in outflow regions (streaks of low wall shear stress). When buoyancy effect dominates on vortex trapping, bubbles rise through the vortices, while spiral patterns stretched along the inner cylinder are clearly identified. Force balance is analyzed to identify dominating forces leading to this accumulation and accumulation patterns are compared with previous experiments.

Bubble puzzles: From fundamentals to applications

“…The left block of data are experiments and numerical simulations for microbubble drag reduction from refs. [214,215,222,223], and the right block of data are our large Re experiments with deformable bubbles [196,205,206].…”

Experimental measurement of oxygen mass transfer and bubble size distribution in an air–water multiphase Taylor–Couette vortex bioreactor

“…For example, if two immiscible liquids are fed continuously to a horizontally oriented Taylor vortex flow cell, a variety of spatial and spatiotemporal hydrodynamic structures arise [35][36][37][38]. More recently it has been reported that the introduction of even a small amount of gas into a vertically oriented Taylor vortex flow cell results in dramatic drag reduction on the rotating inner cylinder and nontrivial gas bubble spatial distribution [39][40][41][42]. Some recent studies have been performed in order to characterize these gas-liquid interactions in Taylor-Couette flows [43][44][45][46].…”

Mixing and axial dispersion in Taylor–Couette flows: The effect of the flow regime

“…The code is based on a finite volume method, and the velocity and pressure (u,P ) are discretized on a staggered nonuniform cylindrical grid. The numerical code has been already used in laminar and turbulent configurations (see details in[33])). The spatial derivatives are computed with second order accuracy, and temporal integration is achieved by a third order Runge-Kutta scheme and a semi-implicit Crank-Nicolson scheme for the viscous terms.…”