Effects of ratchet surfaces on inclined thermal convection

The influence of ratchets on inclined convection is explored within a rectangular cell (aspect ratio $\Gamma_{x}=1$ and $\Gamma_y=0.25$) by experiments and simulations. The measurements are conducted over a wide range of tilting angles ($0.056\leq\beta\leq \pi/2\,\si{\radian}$) at a constant Prandtl number ($\text{Pr}=4.3$) and Rayleigh number ($\text{Ra}=5.7\times10^9$). We found that the arrangement of ratchets on the conducting plate determines the dynamics of inclined convection, i.e., when the large-scale circulation (LSC) flows along the smaller slopes of the ratchets (case A), the change of the heat transport efficiency is smaller than $5\%$ as the tilting angle increases from 0 to $4\pi/9~\si{\radian}$; when the LSC moves towards the steeper slope side of the ratchets (case B), the heat transport efficiency decreases rapidly with the tilting angle larger than blue$\pi/9~\si{\radian}$. By analyzing the flow properties, we give a physical explanation for the observations. As the tilting angle increases, the heat carrier gradually changes from the thermal plumes to the LSC, resulting in different dynamical behavior. In addition, the distribution of the local heat transport also validates the explanation quantitatively. The present work gives insights into controlling inclined convection using asymmetric ratchet structures.