Multiple States in Turbulent Large-Aspect-Ratio Thermal Convection: What Determines the Number of Convection Rolls?

From zonal flow to convection rolls in Rayleigh–Bénard convection with free-slip plates

“…Although it had been observed before that convection rolls with smaller Γ r imply a higher heat transport -e.g. for 2-D RB convection with no-slip plates (van der Poel et al 2012;Wang et al 2018aWang et al , 2020b, for RB convection in an annulus convection cell (Xie, Ding & Xia 2018) and also for Taylor-Couette flow (Huisman et al 2014) -in those cases the observed increase in the transport is typically a couple of per cent, and by far not as large as observed for RB with free-slip plates and large aspect ratio cells as studied here. This difference is due to different plume dynamics and the associated spatial dependence of the local Nusselt number, Nu(x), as we will discuss later.…”

“…2012; Wang et al. 2018 a , 2020 b ), for RB convection in an annulus convection cell (Xie, Ding & Xia 2018) and also for Taylor–Couette flow (Huisman et al. 2014) – in those cases the observed increase in the transport is typically a couple of per cent, and by far not as large as observed for RB with free-slip plates and large aspect ratio cells as studied here.…”

“…Here the free-slip at the plates is crucial to enable the zonal flow; for no-slip boundary conditions, zonal flow is significantly suppressed and it only exists for Γ smaller than roughly 1.2 (van der Poel et al 2014). In our recent extensive numerical simulations using no-slip boundary conditions, we found that zonal flow appears when Γ is smaller than approximately 4/3 (Wang et al 2020b). Note that these values depend on Ra and Pr.…”

“…In our recent extensive numerical simulations using no-slip boundary conditions, we found that zonal flow appears when is smaller than approximately 4/3 (Wang et al. 2020 b ). Note that these values depend on and .…”

Generation of zonal flows in convective systems by travelling thermal waves

“…2014), but only if the ratio of the horizontal to vertical extension of the domain is smaller than a certain value, see Wang et al. (2020 b ) and Wang et al. (2020 a ).…”