We propose a generalized accretion disk viscosity prescription based on hydrodynamically driven turbulence at the critical effective Reynolds number. This approach is consistent with recent re-analysis by Richard & Zahn (1999) of experimental results on turbulent Couette-Taylor flows. This new $beta$-viscosity formulation is applied to both selfgravitating and non-selfgravitating disks and is shown to yield the standard $alpha$-disk prescription in the case of shock dissipation limited, non-selfgravitating disks. A specific case of fully selfgravitating $beta$-disks is analyzed. We suggest that such disks may explain the observed spectra of protoplanetary disks and yield a natural explanation for the radial motions inferred from the observed metallicity gradients in disk galaxies. The $beta$-mechanism may also account for the rapid mass transport required to power ultra luminous infrared galaxies.
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