The effects of shape and reynolds number on drag in the motion of a freely oriented body in an infinite fluid



The drag on freely oriented bodies in motion relative to an infinite fluid is related to the Reynolds number, ReS, by the formula

K = 24ReS + CIRes2

where Res = DsuOρ/μ is formed from the diameter, Ds, of a sphere with the same surface area as the body, and K = 8ρFD/πμ2 is defined as the drag number. The inertial drag coefficient, Cl, is related to shape, orientation, and the Reynolds number. At Reynolds numbers above 2000 the relation is expressed by the formula,

Cl = 2.53 − 0.283e

where Ψ, the surface sphericity, is the ratio of the surface area of a sphere with the same volume to the gurface area of the body. Correlations are also developed for predicting Cl at Reynolds numbers below 2000.