Author(s): C. L. Dancey; P. Kanellopoulos; P. Diplas

Linked Author(s): Panos Diplas

Keywords: Open Channel Flow; Fully Rough Boundary; Turbulence; Logarithmic Velocity Profile

Abstract: The region above the roughness sublayer in fully developed, turbulent, openchannel flow is examined for the case of 2% roughness packing density, and under incipient wall shear stress conditions. It is assumed that the log law for the mean stream-wise velocity is valid in this region and the effect of the roughness geometry and relative depth on the zeroplane displacement, d, and roughness length, z0, (parameters that appear in the log law) is explored. It is found that the introduction of even a small amount of exposed roughness on top of a rough, densely packed sediment bed has a significant effect upon both the zero-plane displacement and the roughness length, in the outer flow. It is also found, for the case of 2% packing density with spherical particles, that z0 decreases with the flow depth; however, the relative roughness, z0/H, increases as the relative depth decreases. The zero-plane displacement is relatively insensitive to relative depth. An increase in the relative wall roughness, z0/H, as the relative depth decreases implies an increase in the wall friction factor, which is consistent with previous measurements of the critical Shields stress for this bed geometry.

DOI:

Year: 2003