Modelling spanwise heterogeneous roughness through a parametric forcing approach

Inhomogeneous rough surfaces in which strips of roughness alternate with smooth-wall are known to generate large-scale secondary motions. Those motions strongest if the strip width is order half-channel height and they a spatial wall shear stress distribution whose mean value can significantly exceed area-averaged homogeneously smooth surface. In present paper it shown that parametric forcing approach (Busse & Sandham, J. Fluid Mech. , vol. 712, 2012, pp. 169–202; Forooghi et al. Intl Heat Flow 71, 2018, 200–209), calibrated data from turbulent channel flows over homogeneous roughness, capture topological features motion protruding recessed (Stroh 885, 2020, R5). However, results suggest model induces slightly larger offset when applied heterogeneous rough-wall conditions. Contrary roughness-resolving simulations, where higher resolution required geometry, be usual direct numerical simulation resulting less computationally expensive simulations for study localized effects. Such employed systematically investigate effect relative protrusion on physical mechanism flow formation related drag increase. It found strong spanwise geometrical difference generally lead guiding formation, topology, different separated by surface strips.