  Granules observed in solar photosphere are believed to be convective and
turbulent, but the physical picture of granular dynamical process remains
unclear. Here we performed an investigation of granular dynamical motions of
full length scales based on data obtained by the 1-meter New Vacuum Solar
Telescope (NVST) and the 1.6-meter Goode Solar Telescope (GST). We developed a
new granule segmenting method, which can detect both small faint and large
bright granules. A large number of granules were detected and two critical
sizes, 265 km and 1420 km, were found to separate the granules into three
length ranges. The granules with sizes above 1420 km follow Gaussian
distribution, and demonstrate "flat" in flatness function, which shows that
they are non-intermittent and thus are dominated by convective motions. Small
granules with sizes between 265 and 1420 km are fitted by a combination of
power law function and Gauss function, and exhibit non-linearity in flatness
function, which reveals that they are in the mixing motions of convection and
turbulence. Mini granules with sizes below 265 km follow power law distribution
and demonstrate linearity in flatness function, indicating that they are
intermittent and strongly turbulent. These results suggest that a cascade
process occurs: large granules break down due to convective instability, which
transport energy into small ones; then turbulence is induced and grows, which
competes with convection and further causes the small granules to continuously
split. Eventually, the motions in even smaller scales enter in a
turbulence-dominated regime.
