Wall-Modelled Large-Eddy Simulations of Flows with Non-uniform Roughness

Flows with non-uniform roughness, in which regions of varying roughness-height are adjacent to each other, occur often in engineering and in the natural sciences. The simplest prototype of heterogeneous roughness is the abrupt transition from a rough patch oriented normal to the flow to a smooth one; this configuration can be found very often in atmospheric boundary layers [1]. Downstream of the transition, an internal boundary layer is formed that can be separated into two regions: an equilibrium inner-layer, in which the flow has adjusted to the change of the wall boundary-condition, and an outer layer, where the flow still has memory of the upstream condition.