Author(s): V. I. Nikora
Linked Author(s): Vladimir Nikora
Keywords: No Keywords
Abstract: A theoretically-based relationship for Darcy-Weisbach's friction factor f is derived and discussed. The derivation procedure is based on the averaging of the Navier-Stokes equation followed by repeated integration. The obtained relationship explicitly shows that the friction factor can be split into at least six additive components, due to: (1) viscous stress; (2) turbulent stress; (3) form-induced stress; (4) flow unsteadiness and spatial heterogeneity of mean velocities (e.g., due to nonuniformity and/or secondary currents); (5) spatial heterogeneity of turbulence characteristics (e.g., due to secondary currents); and (6) vertical heterogeneity of driving forces. The constitutive components account for the roughness geometry and highlight significance of the Reynolds and form-induced stresses in the near-bed region where their values are largest and even more enhanced by a weighting factor. The suggested relationship can guide in better understanding of the resistance mechanisms and in developing their parameterizations and models.
Year: 2009