Sediment erosion in zero-mean-shear turbulence

Overview & Synopsis

Turbulence plays an evident role in particle erosion that in many practical situations superimposes with the action of a mean flow. In this paper, the turbulence effect on particle erosion is studied under zero-mean flow conditions, by using the turbulence generated by an oscillating grid. The stirring grid is located more than two mesh size away from the particle layer. The zero-mean flow below the grid has been qualified by revisiting Matsunaga et al. 1 k − ε model. The turbulence efficiency on the settling/resuspension of the particles is quantified for various turbulence intensities, varying the size, the nature of the particles, and their buoyancy relative to the fluid. We find that the concentrations C of eroded particles collapse fairly well onto a single trend for C ≤ 5 × 10 −2 , when plotted as a function of the ratio between the flux of turbulent kinetic energy (TKE) at the particle bed location and the particle settling flux. Above, the concentrations saturate thus forming a plateau. Particle erosion mechanisms have been investigated in terms of competing forces within an "impulse approach". Horizontal drag versus friction first leads to a horizontal motion followed by a vertical motion resulting from vertical drag and lift versus buoyancy. Particle erosion occurs when both force balances are in favor of motion for a duration of 0.1 to 0.3 Kolmogorov time scale.