Tóm tắt: Large-Eddy-Simulation (LES) is combined with the Immersed-Boundary-Method (IBM) to study bedform initiation and development by turbulent ows over erodible beds under hydrauli-cally smooth conditions. The LES and IBM model was rst validated with test cases of bed shear stress distributions and mean ow elds over xed sinusoidal bed surface in open channel ows. The model was then incorporated with two other modules for sediment ransport and for bed surface volution to conduct test cases of sand wave evolution from at beds in various ow and sediment conditions. Fundamental phenomena, such as formation of the rst sand waves, ripple trains, and equilibrium bedforms, have been successfully reproduced.