Reynolds number dependence of Reynolds and dispersive stresses in turbulent channel flow past irregular near-Gaussian roughness

Direct numerical simulation of turbulent channel flow over random rough surfaces

“…The dispersive stresses obtained from DA are examined in the near-wall region of the rough wall in figure 14. Compared with the Reynolds stresses, the dispersive stresses are mostly confined to the roughness layer, consistent with the observations of Yuan & Jouybari (2018) and Jelly & Busse (2019). For Case R400, is maximum at and drops to zero by , underlining the importance of spatial inhomogeneity in the roughness layer.…”

“…Yuan & Jouybari (2018) note the effects of large surface scales on the dispersive stress from their direct numerical simulation (DNS). Jelly & Busse (2019) examined the Reynolds number dependence of the dispersive stresses for irregular near-Gaussian rough surfaces.…”

On the importance of the drag coefficient modelling in the double averaged Navier-Stokes equations for prediction of the roughness effects

“…is the dispersive stress tensor. This term only play a role in the roughness sublayer and more specifically below the roughness crest, in the roughness wake region as shown by Forooghi et al [12] or Jelly and Busse [48] for instance. In addition, the global contribution of the dispersive stresses to the friction is found to be weak as illustrated by Kuwata and Kawaguchi [49] through DNS of channel flows at Re τ = 600.…”

Non--type behaviour of roughness when in-plane wavelength approaches the boundary layer thickness

“…2015; Forooghi et al. 2017, 2018; Jelly & Busse 2019; Flack, Schultz & Barros 2020). However, for the experiments conducted here, we will look at cases where , conforming to these approximate limits, but where the ratio of in-plane roughness wavelength to boundary layer thickness becomes large.…”