  We perform two- (2D) and three-dimensional (3D) hydrodynamics simulations of
convective oxygen shell-burning that takes place deep inside a massive
progenitor star of a core-collapse supernova. Using one dimensional (1D)
stellar evolution code, we first calculate the evolution of massive stars with
an initial mass of 9-40 $M_\odot$. Four different overshoot parameters are
applied, and CO core mass trend similar to previous works is obtained in the 1D
models. Selecting eleven 1D models that have a silicon and oxygen coexisting
layer, we perform 2D hydrodynamics simulations of the evolution $\sim$100 s
until the onset of core-collapse. We find that convection with large-scale
eddies and the turbulent Mach number $\sim$0.1 is obtained in the models having
a Si/O layer with a scale of 10$^8$ cm, whereas most models that have an
extended O/Si layer up to a few $\times 10^9$ cm exhibit lower turbulent
velocity. Our results indicate that the supernova progenitors that possess a
thick Si/O layer could provide a preferable condition for perturbation-aided
explosions. We perform 3D simulation of a 25 $M_\odot$ model, which exhibits
large-scale convection in the 2D models. The 3D model develops large ($\ell =
2$) convection similar to the 2D model, however, the turbulent velocity is
lower. By estimating the neutrino emission properties of the 3D model, we point
out that a time modulation of the event rates, if observed in KamLAND and
Hyper-Kamiokande, would provide an important information about structural
changes in the presupernova convective layer.
