  Ruelle predicted that the maximal amplification of perturbations in
homogeneous isotropic turbulence is exponential $e^{\sigma \sqrt{Re} t}$ (where
$\sigma \sqrt{Re}$ is the maximal Liapunov exponent). In our earlier works, we
predicted that the maximal amplification of perturbations in fully developed
turbulence is faster than exponential $e^{\sigma \sqrt{Re} \sqrt{t} +\sigma_1
t}$. That is, we predicted superfast initial amplification of perturbations.
Built upon our earlier numerical verification of our prediction, here we
conduct a large numerical verification with resolution up to $2048^3$ and
Reynolds number up to $6210$. Our direct numerical simulation here confirms our
analytical prediction. Our numerical simulation also demonstrates that such
superfast amplification of perturbations leads to superfast nonlinear
saturation. We conclude that such superfast amplification and superfast
nonlinear saturation of ever existing perturbations serve as the mechanism for
the generation, development and persistence of fully developed turbulence.
