Deformable ellipsoidal bubbles in Taylor-Couette flow with enhanced Euler-Lagrange tracking

TL;DR

This study uses advanced numerical simulations to investigate how deformable ellipsoidal bubbles affect drag reduction in Taylor-Couette flow, revealing that bubble deformability enhances wall accumulation and flow control.

Contribution

It introduces a novel coupled Euler-Lagrange and sub-grid deformation model for simulating deformable bubbles in turbulent flow, enabling detailed analysis of their impact on drag reduction.

Findings

Deformable bubbles accumulate near the inner wall, increasing drag reduction.

Bubble deformation enhances resistance to wall-normal motion, promoting wall accumulation.

Stronger bubble deformation correlates with more effective drag reduction.

Abstract

In this work we present numerical simulations of $10^5$ sub-Kolmogorov deformable bubbles dispersed in Taylor-Couette flow (a wall-bounded shear system) with rotating inner cylinder and outer cylinder at rest. We study the effect of deformability of the bubbles on the overall drag induced by the carrier fluid in the two-phase system. We find that an increase in deformability of the bubbles results in enhanced drag reduction due to a more pronounced accumulation of the deformed bubbles near the driving inner wall. This preferential accumulation is induced by an increase in the resistance on the motion of the bubbles in the wall-normal direction. The increased resistance is linked to the strong deformation of the bubbles near the wall which makes them prolate (stretched along one axes) and orient along the stream-wise direction. A larger concentration of the bubbles near the driving wall implies that they are more effective in weakening the plume ejections which results in stronger drag reduction effects. These simulations which are practically impossible with fully resolved techniques are made possible by coupling a sub-grid deformation model with two-way coupled Euler-Lagrangian tracking of sub-Kolmogorov bubbles dispersed in a turbulent flow field which is solved through direct numerical simulations. The bubbles are considered to be ellipsoidal in shape and their deformation is governed by an evolution equation which depends on the local flow conditions and their surface tension.