  The vertical shear instability (VSI) is a robust phenomenon in irradiated
protoplanetary disks (PPDs). The majority of previous numerical simulations
have focused on the turbulent properties of its saturated state. However, the
saturation of the VSI manifests as large-scale coherent radially travelling
inertial waves. In this paper, we study inertial-wave-disk interactions and
their impact on VSI saturation. Inertial-wave linear theory is developed and
applied to a representative global 2D simulation using the Athena++ code. It is
found that the VSI saturates by separating the disk into several radial wave
zones roughly demarcated by corotation resonances (turning points); this
structure also manifests in modest radial variations in the vertical turbulence
strength. Future numerical work should employ large radial domains to
accommodate this radial structure of the VSI, while concurrently adopting
sufficiently fine resolutions to resolve the parametric instability that
attacks the saturated VSI inertial waves.
