Assessment of the Equivalent Sandbed Roughness and the Interfacial Friction Factor in Hole Cleaning With Water in a Fully Eccentric Horizontal Annulus

Abstract

Summary In this study, we have investigated the turbulent flow of water over the sandbed deposited in a horizontal eccentric annulus. The primary objective was to determine the effect of the presence of a sandbed on the parameters strongly involved in the bed-erosion process, such as the local fluid-velocity profiles near the interface, the equivalent sandbed roughness, and the average and the interfacial friction factors. The particle-image-velocimetry (PIV) technique was used to measure the velocity distribution at the water/sandbed interface. The bedload transport of particles caused an abrupt increase in the equivalent sandbed roughness. Analyses of the velocity profiles in the wall units confirmed that the sandbed roughness is variable and can be several times greater than the mean particle size. The interfacial ( fi) and the average friction factors ( fa) were evaluated and compared with flow under the stationary-bed and the bedload-transport conditions. The interfacial friction factor increased dramatically at the onset of the bed erosion. We have also found that depending on the bed height (or the surface area of the bed at the interface), the interfacial friction factor can be significantly different from the average friction factor. The results presented here provide much-needed experimental data for the validation of the mechanistic, semimechanistic (empirical), and numerical [computational-fluid-dynamics (CFD)] models of the bed erosion process. The major conclusion of the study is that the difference between the average and interfacial friction factors should be taken into account for more-realistic multilayer modeling of the hole cleaning.