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I'm working on the gas dynamics of protoplanetary disks. I'm particularly interested in the co-evolution of gas turbulence and dust growth / planet(esimal) formation. My research is based on numerical hydrodynamical simulation and linear analysis.
Gas and dust simulations of the VSI with dynamic cooling rate
Gas and dust simulations of the VSI with dynamic cooling rate
Hydrodynamical simulations of the vertical shear instability with dynamic dust and cooling rateFukuhara, Flock, Okuzumi, Tominaga, (2025).
The vertical shear instability (VSI) in protoplanetary disks affects dust by altering gas cooling and causing vertical diffusion. Global two-dimensional simulations show that VSI-driven turbulence can balance dust settling, mixing, and cooling, forming a thick dust layer near the midplane. This equilibrium depends on dust grain size and dust-to-gas mass ratio, with larger grains or lower ratios suppressing turbulence. Our results, consistent with the semi-analytic model of Fukuhara & Okuzumi (2024), indicate that VSI-driven turbulence may regulate dust growth efficiency in disks.
paper: Fukuhara et al. 2025
Self-consistent model for dust settling and VSI
Self-consistent model for dust settling and VSI
The vertical shear instability (VSI) generates turbulence that affects dust diffusion, while dust distribution also influences VSI turbulence intensity via gas cooling. We develop a semi-analytic model that self-consistently determines vertical dust distribution and VSI turbulence intensity using an empirical formula from our hydrodynamical simulations. This model is used to search for equilibrium dust profiles where turbulence balances settling. We find that if the grains are small, there exists a stable equilibrium dust distribution. However, as the grain size increases, the equilibrium solution vanishes. This runaway settling may explain the highly settled dust rings found in the outer part of some protoplanetary disks.
paper: Fukuhara & Okuzumi. 2024
Semi-analytic model that determines the vertical dust distribution and VSI-driven turbulence strengthFukuhara, Okuzumi, (2024).
Two saturated sates of vertical shear instability
Two saturated sates of vertical shear instability
Simulation of the vertical shear instabilityFukuhara, Okuzumi, Ono, (2023).
We have investigated the exact conditions under which the midplane becomes turbulent due to the vertical shear instability (VSI) by performing hydrodynamical simulations with vertically varying cooling times. We find that the midplane becomes turbulent when the thickness of the midplane VSI-stable layer is thin. We identify two types of final saturated state: (i) T states, characterized by vertical turbulent motion penetrating into the VSI-stable midplane layer, and (ii) pT states, characterized by turbulent motion confined in the unstable layers. These results suggest that the dust can determine VSI-dirven turbulence intensity at the midplane because the cooling time profile depends on the size and spatial profile of dust particles.
paper: Fukuhara et al. 2023
Effects of dust evolution on vertical shear instability
Effects of dust evolution on vertical shear instability
We have quantified the potentially stabilizing effects of dust growth and settling on the vertical shear instability (VSI) based on linear analysis. We find that dust growth , as well as settling, makes the region where the linear VSI operates more confined around the miplane. This suppression of the VSI by dust evolution may promote further dust evoluton in the outer regions of protoplanetary disks.
paper: Fukuhara et al. 2021
Effects of dust growth on the vertical shear instabilityFukuhara, Okuzumi, Ono, (2021).
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