Induced agitation in homogeneous bubbly flows at moderate particle Reynolds number

We investigated the agitation induced in a liquid by quasimonodispersed spherical bubbles. For Re(p) about 10 and for void fractions ranging from 0.002 to 0.1, the axial velocity fluctuation probability density functions happen to be uniquely determined by the velocity variance. In addition, the variance experiences a rupture from a nonlinear to a quasilinear increase with the volumic concentration. It is shown that the presence of a deficit of neighbors in the wake of any test inclusion forces the screening of velocity disturbances at a finite distance X-of order Re(p)/alpha-and that the velocity variance does not depend on the system size when the later is large compared with X. Finally, the bubble-induced agitation happens to be much stronger for quasimonodispersed than for polydispersed size distributions because of the longer interaction duration between pairs in the former case.