The aeroacoustic design of porous trailing-edge inserts for wind turbine noise attenuation requires knowledge of the penetration depth of pressure fluctuations into the porous material. Computationally efficient modeling of the attenuation of unsteady pressure and velocity fluctuations within porous materials will enable improved trailing-edge noise attenuation while minimizing aerodynamic performance loss. Steady models fail to capture the frequency dependence of the attenuation of these fluctuations through the material, while high-fidelity unsteady scale-resolved porous medium models are computationally too expensive for the early-stage design phase. In this study, high-fidelity simulations of a porous material sample subjected to low-amplitude modal inflows are used to evaluate the accuracy of the unsteady Darcy model, which is proposed to fill the gap between high-fidelity unsteady simulations and the steady models for porous medium flows. Two important regimes are identified when considering the local conversion of pressure fluctuations into velocity fluctuations, separated in the frequency domain by a critical frequency. For the investigated porous material and flow conditions, the Strouhal number separating these regimes lies between 0.6 and 1.3 , based on the inflow velocity and porous skeleton strut diameter. Above this critical number, pressure and velocity fluctuation attenuation closely follow the unsteady Darcy model. Below this critical number, the local response of the flow features a strong spatial variation throughout the porous sample. In future research, the underlying mechanism affecting the presence of these spatial variations in the low frequencies will be investigated.
