  One of the important consequences of a newly discovered secular dynamical
evolution process of spiral galaxies (Zhang 1996,1998,1999) is that the
orbiting disk matter receives energy injection each time it crosses the spiral
density wave crest. This energy injection has been shown to be able to
quantitatively explain the observed age-velocity-dispersion relation of the
solar neighborhood stars. We demostrate in this paper that similar energy
injection into the interstellar medium could serve as the large-scale energy
source to continuously power the observed interstellar turbulence and to offset
its downward cascade tendency.
