On the distinct drag and wake of flexible plates with a single perforation

The effect of single perforations and their location on the drag and wake of flexible plates was explored through wind tunnel experiments and numerical simulations. Plates were subjected to uniform flows with low turbulence, and a fixed-size square perforation was placed at various locations along the plate center, resulting in a low porosity ratio (γ ≈ 0.028). A high-frequency, high-resolution load cell captured instantaneous aerodynamic force experienced by the plates, while particle tracking velocimetry (PTV) and particle image velocimetry (PIV) measured plate deformation and wake flow for different Reynolds and Cauchy numbers. PIV results showed that perforated plate wakes exhibited distinct jet-like structures through the square perforation, significantly affecting aerodynamic forces and plate deformation. The jet centerline velocity distribution with respect to downwind distance was influenced by the incoming flow and perforation location. These velocity profiles normalized using effective incoming velocity and corrected perforation half-width revealed their dependence on these factors. A simple first-order formulation was developed to predict the change in drag for flexible plates with various perforation locations and a wide range of incoming velocities. Numerical simulations across a broader range of the Cauchy number supported this formulation, confirming the proposed incoming effective velocities model and separating the effects of Cauchy and Reynolds numbers. These findings may inform the design of flexible structures, defining effective porosity, and establishing a foundation for modeling the complex interaction between flow and low-porosity structures.