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Peer-reviewedCC BY 4.0Monthly Notices of the Royal Astronomical Society

Modelling stellar convective transport with plumes – II. Transport properties of locally and non-locally driven convection

  • Youhei Masada1
  • Tomoya Takiwaki2
  • Nobumitsu Yokoi3
  1. 1Department of Applied Physics, Faculty of Science, Fukuoka University , Fukuoka 814-0180 ,
  2. 2Division of Science, National Astronomical Observatory of Japan (NAOJ) , Osawa, Mitaka, Tokyo 181-8588 ,
  3. 3Institute of Industrial Science, University of Tokyo , Komaba, Meguro, Tokyo 153-8505 ,
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Abstract

We perform 3D hydrodynamic simulations of two idealized convection setups: a cooling-driven model (Model C) and an entropy-gradient-driven model (Model S). The two setups exhibit clear differences: while Model S develops large, relatively stationary eddies excited at depth, Model C is dominated near the surface by intermittent plume-like downflows that produce broad non-Gaussian velocity distributions and a turbulent energy flux that exceeds that in Model S by nearly an order of magnitude in the upper convection zone. Conventional gradient-diffusion (GD) closures reproduce the transport in Model S but significantly underestimate it in Model C, demonstrating that the plume-dominated transport realized in our cooling-driven setup cannot be reproduced by a local, gradient-based model. To address this, we introduce a time-space double averaging method that extracts coherent fluctuations, yielding a diagnostic variable ũ that peaks where the flux is largest. Building on this insight, we propose a modified GD closure in which the turbulent diffusivity is corrected by a plume-mediated term, achieving quantitative agreement with simulation results. Although the closure requires a calibrated model parameter and a careful choice of the averaging window, it provides a physically transparent framework that links coherent plume dynamics to mean-field transport and offers a pathway toward improved subgrid models for non-equilibrium stellar convection zones.

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Cite

BibTeXRIS
BibTeX
@article{masada2026modelling,
  title = {{Modelling stellar convective transport with plumes – II. Transport properties of locally and non-locally driven convection}},
  author = {Youhei Masada and Tomoya Takiwaki and Nobumitsu Yokoi},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {2026},
  month = oct,
  doi = {10.1093/mnras/stag1988},
  url = {https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1988/8965441},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Modelling stellar convective transport with plumes – II. Transport properties of locally and non-locally driven convection
AU  - Youhei Masada
AU  - Tomoya Takiwaki
AU  - Nobumitsu Yokoi
PY  - 2026
DA  - 2026/10/21
JO  - Monthly Notices of the Royal Astronomical Society
DO  - 10.1093/mnras/stag1988
UR  - https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1988/8965441
AB  - We perform 3D hydrodynamic simulations of two idealized convection setups: a cooling-driven model (Model C) and an entropy-gradient-driven model (Model S). The two setups exhibit clear differences: while Model S develops large, relatively stationary eddies excited at depth, Model C is dominated near the surface by intermittent plume-like downflows that produce broad non-Gaussian velocity distributions and a turbulent energy flux that exceeds that in Model S by nearly an order of magnitude in the upper convection zone. Conventional gradient-diffusion (GD) closures reproduce the transport in Model S but significantly underestimate it in Model C, demonstrating that the plume-dominated transport realized in our cooling-driven setup cannot be reproduced by a local, gradient-based model. To address this, we introduce a time-space double averaging method that extracts coherent fluctuations, yielding a diagnostic variable ũ that peaks where the flux is largest. Building on this insight, we propose a modified GD closure in which the turbulent diffusivity is corrected by a plume-mediated term, achieving quantitative agreement with simulation results. Although the closure requires a calibrated model parameter and a careful choice of the averaging window, it provides a physically transparent framework that links coherent plume dynamics to mean-field transport and offers a pathway toward improved subgrid models for non-equilibrium stellar convection zones.
SN  - 0035-8711
SN  - 1365-2966
ER  -