Drag on Nonspherical Objects

Abstract

Stokes's law describes drag force on a sphere in creeping flow. This law can be extended to a nonspherical object by allocating the interaction of the fluid with the object into its interaction with two analogous spheres, one with the same projected area and one with the same surface area as the object. This approach was used to characterize dynamic shape factor for objects whose shape factors are reported in the literature. Agreement between data and the equation for shape factor based on this approach was excellent for prisms: R ² = 0.998. This equation and empirical equations from the literature were used to predict shape factor for a sphere, cylinders, prisms, spheroids, and double conicals whose shape factors have been reported. The equation based on the Stokes's law extension predicted shape factors better than the empirical equations, as judged by a least-squares index of performance.