Hydraulic Resistance of Artificial Strip Roughness

An experimental study of two-dimensional flow over non-uniform roughness is reported in which artificial strip roughness was employed. The roughness elements were square in cross section and placed at different relative spacings. A six-fold classification system is suggested based upon the ideas of Morris and Adachi. Resistance data from other investigators is also considered, and the variation of resistance coefficient with Reynolds number, relative spacing, and relative depth examined. The general resistance parameter, X, first introduced by Sayre and Albertson is found to be particularly helpful in synthesizing the various sets of resistance data. Logarithmic resistance equations involving X are validated over a wide range of roughness wavelength to height ratio. The relationship between roughness height and Nikuradse's equivalent sand roughness size is also examined.