A Re-Evaluation of Schlichting’s Surface Roughness Experiment

Abstract

A re-evaluation of the skin friction coefficient and equivalent sand roughness data reported by Schlichting in 1936 on fourteen rough surfaces is presented. Several assumptions made during the original data reduction are shown to have significant effects on the final results. Additional data and analytical results published since 1936 allow the use of more precise assumptions and enable a re-evaluation of the original data. Corrected results are presented for seventy-nine runs reported by Schlichting on the fourteen surfaces containing spherical, spherical segment and conical roughness elements with various spacings. The original skin friction coefficients are shown to be higher than the corrected values by amounts ranging from 0.5 to 73 percent, while the original equivalent sand roughness values are higher than the corrected ones by 26 to 555 percent. Roughness Reynolds numbers determined using the corrected data indicate that sixteen of the runs on three surfaces were probably in the transitionally rough regime, not the fully rough regime as originally reported.