Bubbles dynamics and their interactions with the walls and the liquid are fully resolved through a four-way coupling strategy. Simulations involve a very large amount of bubbles. DNS strategy gives access to a fine evaluation of the flow in the wall vicinity that is inaccessible in mixture models. The mesh sensitivity has been investigated for cell sizes ranging between 0.7 and 12 bubble radii. No strong differences have been observed between the purely elastic and the non-elastic rebound cases.