  Turbulent combustion is three-dimensional. Turbulence in a Type Ia supernova
is driven on large scales by the buoyancy of burning products. The turbulent
cascade penetrates down to very small scales, and makes the rate of
deflagration independent of the microphysics. The competition between the
turbulent cascade and the freeze-out of turbulent motions due to stellar
expansion determines the largest scale participating in the cascade. This sets
the bulk rate of a deflagration in a supernova. The freeze-out limits the bulk
rate of deflagration to a value that makes a powerful explosion impossible.
Two-dimensional simulations cannot capture these essential elements of
turbulent combustion, even in principle. A powerful delayed detonation
explosion can take place if the burning makes a transition to a detonation. A
deflagration to detonation transition (DDT) can occur in a layer of mixed cold
fuel and hot burning products created either inside an active turbulent burning
region by a high intensity of turbulence, or by mixing cold fuel with ashes of
a dead deflagration front during the global pulsation of a star, or by both.
