Modeling stellar convective transport with plumes : II. Transport Properties of Locally and Non-locally driven Convection
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arXiv
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| Formato: | Preprint |
| Publicado: |
2025
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| author | Masada, Youhei Takiwaki, Tomoya Yoko, Nobumitsu |
| author_facet | Masada, Youhei Takiwaki, Tomoya Yoko, Nobumitsu |
| contents | We perform three-dimensional hydrodynamic simulations of two idealized regimes of stellar convection: a cooling-driven model (Model C) and an entropy-gradient-driven model (Model S). The two regimes exhibit striking contrasts: 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 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 plume-driven convection lies beyond the scope of local, gradient-based models. To address this, we introduce a Time-Space Double Averaging (TSDA) method that extracts coherent fluctuations, yielding a diagnostic variable $\tilde{\boldsymbol{u}}$ 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_12824 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Modeling stellar convective transport with plumes : II. Transport Properties of Locally and Non-locally driven Convection Masada, Youhei Takiwaki, Tomoya Yoko, Nobumitsu Solar and Stellar Astrophysics Fluid Dynamics We perform three-dimensional hydrodynamic simulations of two idealized regimes of stellar convection: a cooling-driven model (Model C) and an entropy-gradient-driven model (Model S). The two regimes exhibit striking contrasts: 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 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 plume-driven convection lies beyond the scope of local, gradient-based models. To address this, we introduce a Time-Space Double Averaging (TSDA) method that extracts coherent fluctuations, yielding a diagnostic variable $\tilde{\boldsymbol{u}}$ 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. |
| title | Modeling stellar convective transport with plumes : II. Transport Properties of Locally and Non-locally driven Convection |
| topic | Solar and Stellar Astrophysics Fluid Dynamics |
| url | https://arxiv.org/abs/2511.12824 |