The stellar hydrodynamic group of Prof Raphael Hirschi at Keele University and their international collaborators computed a series of 3D hydrodynamical simulations of stellar convection during carbon burning (see figure 1). These 3D implicit large eddy simulations were computed with the PROMPI code on the COSMA supercomputer in Durham. The simulations were analysed on-the-fly with PROMPI’s built-in mean-field analysis based on the Reynolds-averaged Navier–Stokes framework (RA-ILES, see Arnett et al 2019 and references therein). Both the vertical convective velocities within the convective region and the bulk Richardson number of the boundaries were found to scale with the driving luminosity as expected from turbulence theory: v ∝ L1/3 and RiB ∝ L-2/3, respectively. The positions of the convective boundaries were estimated through the composition profiles across them, and the strength of convective boundary mixing was determined by analysing the boundaries within the framework of the entrainment law. The entrainment was found to be approximately inversely proportional to the bulk Richardson number, RiB (∝ RiB-a, with a ~0.75). Although the entrainment law does not encompass all the processes occurring at boundaries, the results support the use of the entrainment law to describe convective boundary mixing in 1D models and new 1D models including entrainment show promising results. These large-scale simulations also inform the team’s ongoing theoretical efforts to overcome the shortcomings of the widely used but outdated mixing-length theory (Arnett et al 2019).
