Effect of bubble size in turbulent bubbly downflow in a vertical channel

The effect of bubble size on the properties of downward turbulent flows of bubbly liquids in a vertical channel is examined using direct numerical simulations, where the full Navier–Stokes equations are solved by a parallelized front-tracking/finite-volume method. The turbulent channel flow is driven downward by an imposed constant pressure gradient, and the friction Reynolds number, based on the friction velocity and half-width of the channel, is 127.3. Bubbles of two different sizes, with diameters of 31.8 and 38.2 wall units, are introduced into the turbulent flow with a monodisperse or bidisperse distribution. The results show that for the cases studied here the bubble size has little effect on the void fraction distribution and the mean vertical velocity profile. The average velocity fluctuations and the vorticity profiles across the channel do, however, change.