Deformation, drag, and vortex shedding from a porous membrane disk

Compliant and porous materials like cloth are applied to increase the drag and stability in the design of parachutes. The porosity can stabilize the wake and lead to increased drag. However, the effect of porosity on elastically deforming membranes has not been studied to great extent. As the membrane stretches under pressure the pores expand and increase the flow through the membrane. This gives rise to rich dynamics between fluid and structure. In this study, we present a theoretical model based on experimental data on the interplay between membrane loading, deformation, and leakage of hyper-elastic, porous membrane discs. We perform aerodynamic force measurement of porous membrane discs in wind tunnel experiments to determine the drag variation of membranes with different porosity and material properties. Additional flow field and deformation measurements are conducted to relate the membrane dynamics to the unsteady flow over and through the porous membranes. The added porosity stabilizes oscillations, observed previously in non-porous, compliant membranes. The reduced vortex shedding leads to an overall reduction in unsteady force variation acting on the bulged membranes.