Turbulent channel flow response to elliptical high-roughness patches: a "virtual laboratory" for studying the evolution of large-scale motions

The outer layer of the fully-rough wall-sheared turbulent flow consists of uniform momentum zones (UMZs) of momentum excesses and deficits alternating throughout the vertical direction with a 'stair-case' pattern. This outer-layer flow structure was recently revealed as the outcome of the inner-layer interactions (Anderson and Salesky, 2020: J. Fluid Mech. 906, A8-1—13) interpreted from direct numerical simulation (DNS) of fully-rough channel turbulence (Lee & Moser, 2015: J. Fluid Mech. 860, 886–938). In Zheng and Anderson 2022, the origination of the UMZs is further specified as the interaction from roughness sublayer, utilizing conditional sampling from large eddy simulation (LES) of fully-rough turbulent channel flow. To implement the condition that previously virtualized the phase-locked UMZs, the ongoing work leverages the patch method (with high-roughness patch of elliptical shape) for the extraction and revelation of the roughness impacts. Gaussian distribution of the roughness in streamwise and spanwise dimensions is also included as a counterpart for local-stress-based conditional sampling. We speculate this will be substantial proof in addition to the previous discussion of the UMZ origination.