This study develops a novel rough-wall model for large eddy simulation (LES) based on recent work on wall-modelled LES. This approach is capable of solving for the basic flow character over a rough wall at high Reynolds numbers without resolving the details of the roughness elements. The wall-modelled LES approach on a smooth wall is proven to be sufficiently precise to predict the velocity profile and wall shear stress. The average roughness shear stress can be combined with the smooth-wall shear stress in the inner-layer wall model by defining a roughness shear stress ratio α. The instantaneous shear stresses caused by the roughness elements are calculated by the pressure projection and elevation fields. The total shear stress is fed back to the outer-layer LES mesh as a new boundary condition. The results of the wall-modelled LES correspond well with the experimental data. The comparison between the simulation and experiment reveals that the wall-modelled LES approach presented in this research is capable of predicting the flow in a rough-wall boundary layer without resolving the detailed roughness element geometries.

这项研究基于对壁建模的LES的最新研究，开发了一种用于大涡模拟（LES）的新型粗糙壁模型。这种方法能够解决高雷诺数下粗糙壁上的基本流动特性，而无需解决粗糙度元素的细节。事实证明，在光滑壁上进行壁建模的LES方法足够精确，可以预测速度分布和壁切应力。通过定义粗糙度剪切应力比α，可以将平均粗糙度剪切应力与内层壁模型中的光滑壁剪切应力结合。由粗糙度元素引起的瞬时剪切应力由压力投影场和高程场计算。总剪切应力作为新的边界条件反馈到外层LES网格。壁模型LES的结果与实验数据很好地吻合。仿真与实验的比较表明，本研究中提出的壁模型LES方法能够预测粗糙壁边界层中的流量，而无需解决详细的粗糙元素几何形状。