We perform two-dimensional axisymmetric hydrodynamic simulations of matter mixing in aspherical core-collapse supernova explosions of a 16.3 M _ { \odot } star with a compact hydrogen envelope .
Observations of SN 1987A have provided evidence that ^ { 56 } Ni synthesized by explosive nucleosynthesis is mixed into fast moving matter ( \gtrsim 3,500 km s ^ { -1 } ) in the exploding star .
In order to clarify the key conditions for reproducing such high velocity of ^ { 56 } Ni , we revisit matter mixing in aspherical core-collapse supernova explosions .
Explosions are initiated artificially by injecting thermal and kinetic energies around the interface between the iron core and the silicon-rich layer .
Perturbations of 5 % or 30 % amplitude in the radial velocities are introduced at several points in time .
We found that no high velocity ^ { 56 } Ni can be obtained if we consider bipolar explosions with perturbations ( 5 % amplitude ) of pre-supernova origins .
If large perturbations ( 30 % amplitude ) are introduced or exist due to some unknown mechanism in a later phase just before the shock wave reaches the hydrogen envelope , ^ { 56 } Ni with a velocity of 3,000 km s ^ { -1 } can be obtained .
Aspherical explosions that are asymmetric across the equatorial plane with clumpy structures in the initial shock waves are investigated .
We found that the clump sizes affect the penetration of ^ { 56 } Ni .
Finally , we report that an aspherical explosion model that is asymmetric across the equatorial plane with multiple perturbations of pre-supernova origins can cause the penetration of ^ { 56 } Ni clumps into fast moving matter of 3,000 km s ^ { -1 } .
We show that both aspherical explosion with clumpy structures and perturbations of pre-supernova origins may be necessary to reproduce the observed high velocity of ^ { 56 } Ni .
To confirm this , more robust three-dimensional simulations are required .