One of the remarkable results of recent un-biased transient surveys is the discovery of superluminous supernovae (SLSNe), a special class of SNe characterized by their extreme brightness.  Hydrogen-poor SLSNe are among the most mysterious sub-class, because of their still unknown energy source.  One of the plausible scenarios explaining the extreme brightness of hydrogen-poor SLSNe is the central engine scenario, which assumes that the compact object (neutron star or black hole) left at the center of the SN ejecta deposits additional energy in some way to give rise to bright emission.  We have recently been working on multi-dimensional simulations of the dynamical evolution of SN ejecta with a relativistic wind from the central energy source.  When the total amount of the injected energy is much larger than the original kinetic energy of the SN ejecta, channel flows emanating from the central region result in the energy redistribution and efficient mixing in the ejecta.  We present recent results of our numerical calculations and discuss their implications for observations of hydrogen-poor SLSNe.