Bubble-induced agitation and microstructure in uniform bubbly flows at small to moderate particle Reynolds numbers

The bubble-induced agitation has been quantified in dilute and homogeneous bubbly flows. To characterize the microstructure, experimental techniques have been developed that provide the average perturbed liquid velocity and the pair density. For particulate Reynolds numbers Rep about unity and contaminated bubbles, the liquid agitation is shown to increase as α/Rep where α is the local void fraction. Although in partial agreement with the scaling proposed by Koch (Phys. Fluids, 1993), the pair-density distribution does not exhibit any deficit. On the opposite, experiments at Rep=O(10) and clean bubbles reveal a strong deficit in the rear of test bubbles as well as a moderate accumulation both in a horizontal plane and all along the deficit zone. The extent of the deficit slowly decreases with the void fraction, roughly as α−0.3±0.1. It is shown that the agitation originates from this near wake region, the structure of which strongly differs from the one due to a single inclusion both in terms of its later...