This work describes an experimental investigation on the mixing induced by a swarm of high Reynolds number air bubbles rising through a nearly homogeneous and isotropic turbulent flow. The gas volume fraction α and the velocity fluctuations u 0 ′ of the carrier flow before bubble injection are varied, respectively, in the ranges 0 ≤ α ≤ 0.93% and 2.3 cm/s ≤u 0 ′ ≤5.5 cm/s, resulting in a variation of the bubblance parameter b in the range [0, 1.3] (b=[Formula presented], where V r is the relative rising velocity). Mixing in the horizontal direction can be modelled as a diffusive process, with an effective diffusivity D xx . Two different diffusion regimes are observed experimentally, depending on the turbulence intensity. At low turbulence levels, D xx increases with gas volume fraction α while at high turbulence levels the enhancement in D xx is negligible. When normalizing by the time scale of successive bubble passage, the effective diffusivity can be modelled as a sole function of the gas volume fraction α* ≡ α/α c , where α c is a theoretically estimated critical gas volume fraction. The present explorative study provides insights into modeling the mixing induced by high Reynolds number bubbles in turbulent flows.
|Number of pages||7|
|Journal||International journal of multiphase flow|
|Early online date||20 Mar 2019|
|Publication status||Published - 1 May 2019|