Constrained large-eddy simulation of turbulent flow over rough walls

Recent research indicates that the structure of the wall-bounded turbulence depends on the mean shear created by the wall. To examine the response of the wall turbulence to the rough-wall-like mean shear, we performed numerical tests of the channel flows in the framework of the constrained large-eddy simulation without resolving the roughness elements. Once the rough-wall-like mean shear is imposed, the normalized contribution of the sweep motions to the Reynolds stress increases in the near-wall region and the two-point correlation of the streamwise velocity in the outer layer is enhanced. The constraint of the rough-wall-like mean shear provides extra resistance just like the surface roughness, which is observed via the decomposition of the skin friction coefficient. All the statistics indicate that the effect of the rough-wall-like mean shear on the turbulent flow is similar to the effect of roughness elements. The large-eddy simulations of the rough-wall flows using the conventional equilibrium-wall model are also performed for comparison. The statistical results in the outer layer are qualitatively consistent with those obtained by constraining the mean shear, which demonstrates the latter approach can be used as a new wall model for the simulation of the rough-wall flows.