We are interested in the phase separation of a light fluid in a heavier fluid in a closed box. A simple initial configuration is considered. A cubic volume of light fluid with a characteristic length H/2 is contained in the bottom part of a cubic box of side H filled with a heavier fluid. This problem is typical of multiscale interfacial flows in which large interfacial scales coexist with small dispersed droplets interacting with larger drops according to coalescence or rupture of interfaces. A benchmark of phase separation is proposed here. Several CFD codes devoted to multiphase flow simulations are evaluated on DNS simulations for different meshes. The VOF method, the level set method and the AMR method are used for tracking interface, the final objective being to see if codes using different numerical methods converge to the same macroscopic quantities. Time evolution of potential energies, kinetic energies, and interfacial area are computed for each simulation and used for codes comparisons. These physical quantities are also used to ensure that grid convergence is achieved. The phase separation also induces turbulence effects. In order to quantify it, time evolution of enstrophy is evaluated for each simulation. It is shown that all the codes converge for all macroscopic quantities for two turbulent Reynolds numbers, except for enstrophy. This difference is due to an under resolution of the vorticity.