Impact of spanwise effective slope upon rough-wall turbulent channel flow

Whereas streamwise effective slope ( $ES_{x}$ ) is accepted as a key topographical parameter in the context of rough-wall turbulent flows, significance its spanwise counterpart $ES_{y}$ remains largely unexplored. Here, response channel flow over irregular, three-dimensional rough walls with systematically varied values studied using direct numerical simulation. All simulations were performed at fixed friction Reynolds number 395, corresponding to viscous-scaled roughness height $k^{+}\approx 65.8$ (where $k$ mean peak-to-valley height). A surface generation algorithm used synthesise set ten irregular surfaces specified for three different . share common and are near-Gaussian, which allows this study focus on impact varying , since amplitude, skewness can be eliminated simultaneously parameters. Based an analysis first- second-order velocity statistics, well turbulence co-spectra fractional contribution pressure viscous drag, shows that strongly affect drag penalty – particularly low- surfaces. secondary observation particular lead diminished levels outer-layer similarity both attributed insufficient scale separation between outer length in-plane wavelength.