Abstract
Context. In recent years hydrodynamical (HD) models have become important to describe the gas kinematics in protoplanetary disks, especially in combination with models of photoevaporation and/or magnetically driven winds. Our aim is to investigate how vertical shear instability (VSI) could influence the thermally driven winds on the surface of protoplanetary disks. Aims. In this first part of the project, we focus on diagnosing the conditions of the VSI at the highest numerical resolution ever recorded, and suggest at what resolution per scale height we obtain convergence. At the same time, we want to investigate the vertical extent of VSI activity. Finally, we determine the regions where extreme UV (EUV), far-UV (FUV), and X-ray photons are dominant in the disk. Methods. We perform global HD simulations using the PLUTO code. We adopt a global isothermal accretion disk setup, 2.5D (2 dimensions, 3 components) which covers a radial domain from 0.5 to 5.0 and an approximately full meridional extension. Our simulation runs cover a resolution from 12 to 203 cells per scale height. Results. We determine 50 cells per scale height to be the lower limit to resolve the VSI. For higher resolutions, ≥50 cells per scale height, we observe the convergence for the saturation level of the kinetic energy. We are also able to identify the growth of the “body” modes, with higher growth rate for higher resolution. Full energy saturation and a turbulent steady state is reached after 70 local orbits. We determine the location of the EUV heated region defined by Σr = 1019 cm−2 to be at HR ~ 9.7 and the FUV–X-ray heated boundary layer defined by Σr = 1022 cm−2 to be at HR ~ 6.2, making it necessary to introduce a hot atmosphere. For the first time we report the presence of small-scale vortices in the r − Z plane between the characteristic layers of large-scale vertical velocity motions. Such vortices could lead to dust concentration, promoting grain growth. Our results highlight the importance of combining photoevaporation processes in the future high-resolution studies of turbulence and accretion processes in disks.
Highlights
Hydrodynamical (HD) simulations in protoplanetary disks have gained substantial attention during the last decades
For resolutions higher than 12 cells per scale height, the growth seen at ≥25 orbits is characteristic of the initial increase phase of the kinetic energy as the disk become unstable to the vertical shear instability (VSI), as found by Nelson et al (2013)
We performed 2.5D hydrodynamical simulations for an isothermal accretion disk with different resolutions, up to 203 cells per scale height to fully resolve for the VSI
Summary
Hydrodynamical (HD) simulations in protoplanetary disks have gained substantial attention during the last decades. The presence of vertical shear instability (VSI; Goldreich & Schubert 1967; Fricke 1968) in purely HD accretion disks has been well studied by careful perturbational analysis and numerical simulations in several works (e.g., Nelson et al 2013; Stoll & Kley 2014; Barker & Latter 2015; Lin & Youdin 2015). The detection of the NeII line from the surface of TW Hya at around 10 AU (Pascucci et al 2011), shows the important influence of high-energy photons on the surface layers of the disk; the vertical extension of the wind is still quite inconclusive. Ballabio et al (2020) found the synthetic line profile of NeII to be consistent with thermally driven winds, while
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