Experimental Investigation on the Settling Velocity and Drag Coefficient of Irregularly Shaped Coral Particles

This study experimentally investigated the settling and drag characteristics of porous and irregularly shaped coral particles with sizes ranging from 0.59 to 8.32 mm. Shape characteristics and settling velocities of these particles were quantified through the utilization of microimage analysis and a settling tube, respectively. It was found that the particle shape significantly influenced the settling velocity and drag coefficient, alongside the particle diameter. With the increase in Reynolds number, the settling motions of the particles gradually intensified and became chaotic, influencing the settling velocity by reducing the vertically projected area and changing the flow fields around. Furthermore, it was observed that particle shape could affect the trend of drag coefficient by amplifying the effect of form drag. Based on the measured data, an empirical formula was proposed to predict the drag coefficient and settling velocity of coral particles. This formula separately considers the impacts of particle shape on the form and friction drag and has the highest prediction accuracy for coral particles compared with other formulas.