Spatial and temporal scales of force and torque acting on wall-mounted spherical particles in open channel flow Articles uri icon

publication date

  • July 2013

start page

  • 2

issue

  • 075103

volume

  • 25

International Standard Serial Number (ISSN)

  • 1070-6631

Electronic International Standard Serial Number (EISSN)

  • 1089-7666

abstract

  • Data from direct numerical simulation of open channel flow over a geometrically rough wall at a bulk Reynolds number of Re-b = 2900, generated by Chan-Braun et al. ["Force and torque acting on particles in a transitionally rough open-channel flow," J. Fluid Mech. 684, 441-474 (2011)] are further analysed with respect to the time and length scales of force and torque acting on the wall-mounted spheres. For the two sizes of spheres in a square arrangement (11 and 49 wall units in diameter, yielding hydraulically smooth and transitionally rough flow, respectively), the spatial structure of drag, lift, and spanwise torque is investigated. The auto-correlation and spectra in time as well as the space-time correlation and convection velocities are presented and discussed. It is found that the statistics of spanwise particle torque are similar to those of shear stress at a smooth wall. Particle drag and lift are shown to differ from spanwise particle torque, exhibiting considerably smaller time and length scales; the convection velocities of drag and lift are somewhat larger than those of spanwise torque. Furthermore, correlations between the flowfield and particle-related quantities are presented. The spatial structure of the correlation between streamwise velocity and drag/spanwise torque features elongated shapes reminiscent of buffer-layer streaks. The correlation between the pressure field and the particle drag exhibits two opposite-signed bulges on the upstream and downstream sides of a particle.

keywords

  • torque; aerodynamics; convection; turbulent flows; channel flows; particle fluctuations; correlation functions; spatial analysis; hydrodynamics; reynolds stress modeling