Reduced-complexity models for turbulent flows over anisotropic porous materials

Structured porous materials have the potential to reduce skin friction, delay separation, and regulate heat transfer in turbulent flows. The design of porous materials for these flow control applications often relies on the use of models grounded in the Darcy-Brinkman-Forchheimer (DBF) framework, whereby the effect of the porous materials is introduced via bulk properties such as permeability. These bulk representations provide incomplete characterizations of the flow in regions with strong spatial inhomogeneity, such as the interface between a porous substrate and an unobstructed flow. This talk considers the use of the DBF framework for resolvent analysis of turbulent flows over anisotropic porous substrates. Using bulk representations, resolvent analysis yields reasonable predictions for the emergence of spanwise-coherent rollers resembling Kelvin-Helmholtz vortices. However, reproducing the effect of the porous substrate on the energetic near-wall cycle requires consideration of the interfacial geometry and its impact on the mean velocity profile. Simple phenomenological models that can capture the effect of interfacial geometry for mean profile predictions and subsequent analyses are developed and tested.