By performing 2.5-dimensional special relativistic radiation magnetohydrodynamics simulations , we study the super-critical accretion disks and the outflows launched via the radiation force .
We find that the outflow is accelerated by the radiation flux force , but the radiation drag force prevents the outflow velocity from increasing .
The outflow velocity saturates around 30 - 40 \% of the light speed around the rotation axis , since then the flux force balances with the drag force .
Our simulations show that the outflow velocity is kept nearly constant in the regime of \dot { M } _ { BH } \sim 10 ^ { 2 - 3 } L _ { Edd } / c ^ { 2 } , where \dot { M } _ { BH } is the mass accretion rate , L _ { Edd } is the Eddington luminosity , and c is the light speed .
Such a faster outflow is surrounded by a slower outflow of \sim 0.1 c .
This velocity is also determined by force balance between the radiation flux force and the radiation drag .
The radiation drag works to collimate the slower outflow in cooperation with the Lorentz force , although the faster outflow is mainly collimated by the Lorentz force .
The kinetic energy is carried by the slower outflow rather than by the faster outflow .
The total kinetic luminosity of the outflow as well as the photon luminosity is \sim L _ { Edd } , almost independent of the mass accretion rate .