On the Roughness Functions of Various Roughened Surfaces and Increase of Skin Friction Resistance

Abstract

The paper deals with the new attempt to find the relationship between the roughened surfaces configuration and it's roughness function. In order to research, two ideas are introduced. One is the roughness height corrected by k/L and other is the roughness Reynolds number described by k^2/Lin place of k, where k is measured roughness height and L is spacing between roughness elements or apparent wave length. The new roughness functions are calculated in two cases, the elementary roughness type and the painted roughness type, using several experimental data which include authors' experimental results for roughened pipe flow. These are fairly convergent compared to the previous method. Further, a fitting approximation is introduced on the roughness function of painted surfaces, and finary, as an application the increase of frictional resistance of a newly built ships and the speed loss of ships in service are calculated using above approximate roughness function.