Settling velocity of non-spherical hydrochorous seeds

Abstract

The settling velocity of irregular particles is affected by both particle properties (density, size, and shape) and fluid properties (density and viscosity) and is therefore a function of particle Reynolds number and particle shape. Experimental data from the literature have been collected on a wide range of particle Reynolds numbers (0.03–10,000) to develop empirical formulae for drag coefficients and settling velocities of non-spherical particles. Three shape factors were adopted and different dimensions of descriptors were recommended according to the types of particles. For coarse particles with large dimensionless diameter, the effect of shape on settling velocity is more significant, and thus piecewise formulae were derived to further improve prediction accuracy. Compared with other models, the newly presented formulae predict more accurately the settling velocity of irregular particles. Moreover, settling velocities of three types of hydrochorous seeds collected from Poyang Lake were measured in the laboratory and the comparison between the measured and predicted settling velocity shows that the empirical formulae can be applied to non-spherical granular hydrochorous seeds and can enrich the study on the dynamic pattern of hydrochory.