Restricted Nonlinear Large Eddy Simulations of Turbulent Flow over Spanwise Heterogeneous Strip Roughness*

Turbulent flow over heterogeneous rough surfaces arise in a wide range of natural and engineering applications ranging from atmospheric boundary layer flow over a forest or crop fields and flow over bio-fouled ship hulls to engineered herringbone riblets to induce turbulent drag reduction. This range of applications hampers a full understanding of the phenomena due to the difficulty in simulating the vast range of phenomena of configurations which roughness topographies can take. Recently, the Restricted Nonlinear Large Eddy Simulation (RNL-LES) framework has been applied to study flow over spanwise heterogeneous strip roughness at arbitrarily high Reynolds numbers [1]. In this work, we take advantage of the computational tractability of the RNL-LES to perform an extensive parametric study of flow over spanwise heterogeneous strip roughness, varying number of repeating roughness units and strip widths. We highlight the importance of circulation in this flow and use the data from the parametric sweep to characterize the influence of intensified secondary flow mixing has on turbulent statistics and momentum transfer. We then use these results to inform a parametric model to predict secondary flow circulation for a given roughness topography.