LARGE-EDDY SIMULATION AND DOUBLE-AVERAGING ANALYSIS OF OPEN-CHANNEL FLOW OVER A PERMEABLE BED

This study focuses on the double-averaging (DA) turbulence characteristics of flow over an idealized permeable bed using the large-eddy simulation (LES). To discuss the spatial heterogeneity, the vertical distributions of DA velocity, DA Reynold shear stress (RSS), DA form-induced shear stress (FISS) and turbulence intensities in different positions are analyzed. It is shown that the spatial heterogeneity has a little influence in the upper flow region, and the distribution of DA velocity corresponds to the logarithmic law. The Von Karman constant obtained is significantly less than the normal value because of permeability. In the vicinity of bed, the spatial heterogeneity has a significant effect on the velocity distributions, which match with a polynomial series and a linear series respectively. Within the permeable bed, the peak velocity at lower pore is 1.55 times larger than that at upper pore. Above the crest bed level, the DA Reynolds shear stress is 95% of the total DA shear stress. The DA form-induced shear stress is 15% of the total DA shear stress occurring at the virtual bed level. The distributions of turbulence intensities in different positions show some discrepancies, which result from the spatial heterogeneity.