Turbulence Anisotropy in Flow at an Entrainment Threshold of Sediment

Abstract

The turbulence anisotropy in flow over noncohesive sediment beds at an entrainment threshold, as compared to that over immobile beds, is studied. The streamwise component of anisotropy tensor in near-bed flow for threshold beds yields more anisotropic stream as compared to that for immobile beds, whereas all other components of anisotropy tensor in near-bed flow for threshold beds yield less anisotropic stream. The anisotropic invariant maps illustrate the anisotropy in near-bed flow layer tending to be a two-component isotropy for both immobile and threshold beds. The data plots for immobile beds with an increase in vertical distance have an affinity to a one-component isotropy, whereas those for mobile beds show a tendency to become a three-dimensional isotropy near the midportion of the flow depth. Invariant function plots show a better two-dimensional isotropy in the inner layer of flow and a quasi-three-dimensional isotropy in the outer layer of flow over threshold beds than those over immobile beds.