A rational approach to drag prediction of spherical and nonspherical particles

Abstract

In the past, general formulas for calculating the drag coefficient for both spherical and nonspherical particles have involved a dependence on a Reynolds number ( Re) and one or more shape descriptors resulting in complicated functions of at least two variables. This paper shows that both the Stokes' shape factor ( K 1) and the Newton's shape factor or scruple ( K 2) are important for the prediction of drag. However, instead of requiring a function of three variables ( Re, K 1, K 2) to predict drag, a function only of the generalized Reynolds number ReK 1 K 2 is needed. The shape factors K 1 and K 2 are then modeled as functions of the geometric shape descriptors' sphericity and the projected area in the direction of motion. Goodness of fit to experimental data is calculated and compared with a recently determined formula.