An analysis of the extensive literature on non-steady drag forces supports the correlation of the data by means of a total drag coefficient, which appears to be a function of the Reynolds Number and of a reduced time parameter which is related to the number of particle diameters traversed since the initiation of the motion. The added mass concept is shown to be both completely inadequate and theoretically unsound. An increase in wake turbulence resulting from Reynolds Number increases or from the occurrence of surface roughness seems to diminish the acceleration effects.
Fundamental studies of the flow fields around blunt bodies reveal the extreme complexity of the phenomena occurring during acceleration. Explanations offered for the characteristics of the non-steady drag coefficient behavior re shown to be frequently at variances with these findings.