2011/08/30 by Clemens Chan-Braun, Manuel García‐Villalba, Manuel García-Villalba +1 · 3 citations
Engineering · Environmental Science · Physics and Astronomy · #Classical mechanics #Drag #Flow (mathematics) #Fluid Dynamics and Turbulent Flows #Hydrology and Sediment Transport Processes #Lift (data mining) #Mechanics #Open-channel flow #Particle Dynamics in Fluid Flows #Physics #Reynolds number #SPHERES #Thermodynamics #Torque #Turbulence #physics.flu-dyn
paper · pdf · doi:10.1017/jfm.2011.311
published as J. Fluid Mech., 684:441-474, 2011 · accepted for publication in J. Fluid Mech. (2011)
arxiv created 2011/08/30 · openalex publication_date 2011/09/13 · arxiv updated 2013/01/28 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Abstract Direct numerical simulation of open channel flow over a geometrically rough wall has been performed at a bulk Reynolds number of Reb ≈ 2900 . The wall consisted of a layer of spheres in a square arrangement. Two cases have been considered. In the first case the spheres are small (with diameter equivalent to 10. 7 wall units) and the limit of the hydraulically smooth flow regime is approached. In the second case the spheres are more than three times larger ( 49. 3 wall units) and the flow is in the transitionally rough flow regime. Special emphasis is given to the characterisation of the force and torque acting on a particle due to the turbulent flow. It is found that in both cases the mean drag, lift and spanwise torque are to a large extent produced at the top region of the particle surface. The intensity of the particle force fluctuations is significantly larger in the large-sphere case, while the trend differs for the fluctuations of the individual components of the torque. A simplified model is used to show that the torque fluctuations might be explained by the spheres acting as a filter with respect to the size of the flow scales which can effectively generate torque fluctuations. Fluctuations of both force and torque are found to exhibit strongly non-Gaussian probability density functions with particularly long tails, an effect which is more pronounced in the small-sphere case. Some implications of the present results for sediment erosion are briefly discussed.