Lift and drag coefficients of deformable bubbles in intense turbulence determined from bubble rise velocity

Abstract

We experimentally investigate the rise velocity of finite-sized bubbles in turbulence with a high energy dissipation rate of $\unicode[STIX]{x1D716}\gtrsim 0.5~\text{m}^{2}~\text{s}^{-3}$ . In contrast to a 30–40 % reduction in rise velocity previously reported in weak turbulence (the Weber number ( $We$ ) is much smaller than the Eötvös number ( $Eo$ ); $We\ll 1<Eo$ ), the bubble rise velocity in intense turbulence shows a surprising new behaviour: an abrupt transition from an order of magnitude slower to a factor of two faster than rising in an otherwise quiescent medium. This transition occurs when $We$ increases from below one to above one, underscoring the key role played by the turbulence-induced deformation. We also formulate a model based on bubble–eddy coupling, and the results show an excellent agreement with not only our data in intense turbulence but also other works on weak turbulence. The model also helps us to extract the lift and drag coefficients of bubbles in intense turbulence for a wide range of $We$ and Reynolds numbers in situ.