Experimental investigation about the incipient velocity of spherical particles on a hemispherical bed surface

The sediment particles play a huge role in shaping the bed load transport. In this research, 240 water-tunnel experiments are carried out to investigate the incipient velocity of the observation particles in two particle arrangements. To accurately predict the incipient velocity of the observation particles, the equation is conceived by the rolling instability mechanism. The incipient velocity equations and experimental data are used to analyze the trend of dispersive pressure and the effect of arrangement position on velocity. We find that it is appropriate to choose the coefficient of drag as 0.261 and the coefficient of lift as 0.198 for the incipient velocity equation of spherical particles on the hemispherical bed surface. Furthermore, the dispersive pressure is closely related to the flow state, particle size, and particle arrangement, which leads to the incipient velocity of the observation particle being at a minimum when the interference particle angle is 45°. Finally, the particle spacing and the projected area changed with the arrangements, directly affecting the incipient velocity of the observed particle. The analysis of four aspects for the coefficients, dispersive pressure, different particle spacing, and projected area will facilitate the prediction of particle incipient velocity, especially on hemispherical beds.