The drag on freely oriented bodies in motion relative to an infinite fluid is related to the Reynolds number, Re S , by the formula K = 24Re S + C I Re s 2 where Re s = D s u O ρ/μ is formed from the diameter, D s , of a sphere with the same surface area as the body, and K = 8ρF D /πμ 2 is defined as the drag number. The inertial drag coefficient, C l , is related to shape, orientation, and the Reynolds number. At Reynolds numbers above 2000 the relation is expressed by the formula, C l = 2.53 − 0.283e 2Ψ 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 C l at Reynolds numbers below 2000.
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H. A. Becker (1959) studied this question.