Fundamental aspects of solids‐gas flow: Part IV: The effects of particle rotation, roughness and shape

This paper examines the various complicating effects which rotation, surface roughness and shape impose on the motion and drag of single particles entrained in a fluid. In general, rotation appears to have little effect on the drag coefficient at low Reynolds Numbers, but influences the linearity of the motion and may thus play a part in the mechanism of particle entrainment in conveyed solids‐gas systems. Negative lift has been observed in the critical Reynolds Number region as the result of asymmetry in the wake structure. Surface roughness will cause an early transition to a turbulent boundary layer at higher Re values, which will result in an appreciable decrease in drag coefficient, but it may increase the drag at low Reynolds Numbers. The effect of particle shape is more complex than has been suggested by previously published analyses. The available empirical correlations are discussed and compared, and indicate a dependency on the particle‐to‐fluid density ratio.