Affilliations: 1University of Exeter; 2Durham University References: [1]: Goluskin, D. et al., ‘Convectively Driven Shear and Decreased Heat Flux’. Journal of Fluid Mechanics 759 (1 November 2014): 360–85 [2]: Burns, K. J. et al., , "Dedalus: A Flexible Framework for Numerical Simulations with Spectral Methods," Physical Review Research 2 (23 April 2020): 023068 [3]: Orvedahl, R. et al., ‘Prandtl-number Effects in High-Rayleigh-number Spherical Convection’. ApJ 856 (20 March 2018): 13 [4]: Currie, L. et al., ‘Convection with misaligned gravity and rotation: simulations and rotating mixing length theory’. MNRAS 493 (10 February 2020): 5233-5256 [5]: Brown, B. P. et al., ‘Rapidly Rotating Suns and Active Nests of Convection’. ApJ 689 (20 December 2008): 1354-1372 Implications Sun Ra ≈ 1020 Pr ≈ 10-7 [3] - Astrophysical values for Ra and Pr are inaccessible to direct numerical simulations - Mixing Length theory is widely employed in astrophysics to model convection (e.g. [4]) but assumes a particular 𝑁𝑢(Ra) relationship and does not take shear into account - If realised in a star, shear would likely effect the entropy gradient and other aspects of interior convection So, can stars shear? 3D isotropic convection does not appear to establish shearing states. However… - Rotation and magnetism can make convection more anisotropic, forcing quasi-2D behaviour in nature (e.g. [5]) - These cases may allow for ‘bursts’ of shear damping vertical transport as described here. We intend to investigate the 3D, rapidly rotating equivalents of these states in future work Fig 2: Temperature snapshots from numerical simulations showing “normal” convection (left) and ”shearing” (right) Fig 1: A schematic comparing “normal” convection and “shearing” convection All stars transport heat by convection and the efficiency of this transport is affected by (among other things) shear flows 2-D Rayleigh-Bénard convection has been observed to drive horizontal ‘shearing’ flows These flows are characterised by very little vertical convective energy transport These flows can be reproduced in numerical simulations, and have been explored for Prandtl number greater than unity [1] We present numerical simulations of Rayleigh-Bénard convection for Prandtl numbers less than 1, to better approximate the astrophysical environment What is Shearing Convection? Fig 3: Comparisons of diagnostic quantities for Pr=0.1 (left) and Pr=0.01 (right). A triangle represents a shearing case, and a circle is a non-shearing case Results Shearing states are readily established in low Pr convection The Pr=0.1 cases make it clear that shearing cases are described by a different 𝑁𝑢Ra relationship that non-shearing cases The vertical heat transport is radically altered by the presence of strong shear The Dedalus pseudo-spectral code [2] was used with periodic boundary conditions to simulate a range of parameters (left) for one viscous time Table 1: The simulated parameters. A tick represents cases with shearing flows. The shaded boxes were not simulated Rayleigh number (Ra) is a measure of flow buoyancy – higher means more convective driving Prandtl number (Pr) is the ratio of viscosity to thermal diffusivity Nusselt number (𝑁𝑢) is the time-averaged ratio of convective to conductive flux at a boundary - 𝑁𝑢=1 corresponds to pure conduction; the larger the value of 𝑁𝑢the more vigorous the convection Dimensionless Definitions Our Simulations Fig 3: Instantaneous Nusselt Number 𝑁𝑢(𝑡) for a non-shearing (left) and a shearing (right) case An Investigation Into Convectively Driven Shear At Low Prandtl Number Tom Joshi-Cale1 Matthew Browning1 | Simon Lance1 | Laura Currie 1,2 tj294@Exeter.ac.uk TomJoshiCale Pr \ Ra 1e4 5e4 1e5 3e5 5e5 1e6 0.1 0.01