Friction Factor For Two-Dimensional Dune Roughness

Abstract

Using dimensional analysis, the flow resistance for the case of two-dimensionaluniform flow in the dune regime was expressed in terms of bed-form geometry,sand size and flow condition. Experiments were conducted in a rectangular flumeusing artificial bed forms. The results showed that the flow resistance is affectedby the sand-grain roughness only when the dunes are flat. When dunes aresteep, the flow resistance is due mainly to the form drag and is relativelyconstant. The results also showed that the friction factor obtained by addingthe friction factor due to a plane sand bed and that due to form drag is likelyto be too large if the dunes are steep. It has also been demonstrated that thedune length to depth ratio has a significant effect on the friction factor whenthe dunes are steep. The experimental data were compared with results from otherinvestigators.