Classical and symmetrical horizontal convection: detaching plumes and oscillations

Classical and symmetrical horizontal convection is studied by means of direct numerical simulations for Rayleigh numbers Ra up to 3 × 1012 and Prandtl numbers Pr = 0.1, 1 and 10. For both set-ups, a very good agreement in global quantities with respect to heat and momentum transport is attained. Similar to Shishkina & Wagner (Phys. Rev. Lett., vol. 116, 2016, 024302), we find Nusselt number N u versus Ra scaling transitions in a region 108 ≤ Ra ≤ 1011. Above a critical Ra, the flow undergoes either a steady–oscillatory transition (small Pr) or a transition from steady state to a transient state with detaching plumes (large Pr). The onset of the oscillations takes place at Ra Pr-1 ≈ 5 x 109 and the onset of detaching plumes at Ra Pr5/4 ≈ 9 x 1010. These onsets coincide with the onsets of scaling transitions