The effect of spanwise heterogeneous surfaces on mixed convection in turbulent channels

Turbulent mixed convection in channel flows with heterogeneous surfaces is studied using direct numerical simulations. The relative importance between buoyancy and shear effects, characterized by the bulk Richardson number $Ri_b$, varied order to cover flow regimes of forced, natural convection, which are associated different large-scale organization. surface consists streamwise-aligned ridges, known induce secondary motion case forced convection. streamwise rolls emerging under smooth-wall conditions significantly affected their appearance considerably reduced for dense ridge spacings. It found that formation these requires larger forces than over smooth walls due additional drag induced ridges. Therefore, transition from structures delayed towards $Ri_b$ spanwise surfaces. influence on organization particularly pronounced roll-to-cell range, where ridges favor convective cells at lower $Ri_b$. In addition, observed align perpendicular decreasing spacing. We attribute this reorganization fact parallel experience less across energetically more beneficial. Furthermore, we find exhibit very slow dynamics $Ri_b=1$ $Ri_b=3.2$ when spacing rolls' width. For cases up- downdrafts move slowly entire instead being fixed space as cases.