Drag forces on a bed particle in open-channel flow: effects of pressure spatial fluctuations and very-large-scale motions
SM Cameron, V Nikora, I Marusic
JOURNAL OF FLUID MECHANICS | CAMBRIDGE UNIV PRESS | Published : 2019
The fluctuating drag forces acting on spherical roughness elements comprising the bed of an open-channel flow have been recorded along with synchronous measurements of the surrounding velocity field using stereoscopic particle image velocimetry. The protrusion of the target particle, equipped with a force sensor, was systematically varied between zero and one-half diameter relative to the hexagonally packed adjacent spheres. Premultiplied spectra of drag force fluctuations were found to have bimodal shapes with a low-frequency peak corresponding to the presence of very-large-scale motions (VLSMs) in the turbulent flow. The high-frequency region of the drag force spectra cannot be explained b..View full abstract
Awarded by EPSRC/UK
The study has been supported by two EPSRC/UK grants, 'High-resolution numerical and experimental studies of turbulence-induced sediment erosion and near-bed transport' (EP/G056404/1) and 'Bed friction in rough-bed free-surface flows: a theoretical framework, roughness regimes, and quantification' (EP/K041088/1). I.M. also acknowledges the support of the Australian Research Council.