Gravitoturbulent viscosity
= Gravitoturbulent viscosity
A mixing-length estimate for gravitational turbulence takes the largest unstable wavelength $\ell$ and orbital growth rate $\Omega$, giving turbulent velocity $u_{\rm turb}\sim\Omega\ell$ and kinematic viscosity $\nu\sim u_{\rm turb}\ell\sim\Omega\ell^2$.