  A dynamical model is proposed for isotropic turbulence driven by steady
forcing that yields a viscosity independent dynamics for the small-scale
(inertial) regime. This reproduces the Kolmogorov spectrum for the two-point
velocity correlation function in the fully developed (stationary) stage, while
predicting intermittency corrections for higher order moments. The model also
yields a transient stage with a power-law time evolution. The crossover time to
fully developed turbulence scales with the turbulent system size as $\sim
L^{11/3}$. The physical origin of the transient behavior is explained.
