Particle motion over a smooth bed: effect of shape

We experimentally investigated the effect of particle shape on saltation over a smooth bed. The particle shapes considered included spheres, ellipsoids, ellipsoidal cylinders, and prisms, all having the same weight and nominal diameter. The Corey’s shape factor, varied from 0.2 (deformed prism) to 1 (sphere). We studied its effects on several Lagrangian indicators. The probability distribution function (pdf) of the streamwise velocity u transitions from Gaussian-like (SF=1) to gamma-like as the shape factor decreases. Specifically, the mean and variance of u increase and decrease, respectively, with increasing shape factor. The pdf of the transversal velocity v remains Gaussian-like, with zero mean, and its variance shows a negative correlation with the shape factor. The autocorrelation function of u is independent of the shape factor, with an average integral time scale of 0.5 s. In contrast, the autocorrelation function of v depends on the shape factor. We also computed the streamwise and transversal mean square displacements. In the streamwise direction, the behaviour is consistently super-diffusive, with an exponent of 0.83 for t<1 s and 0.63 for larger times. In the transversal direction, diffusion is normal for t>1 s. At small time scales, the diffusion regime is normal for low shape factors and super-diffusive for high shape factors.