Simulations of flow past a mirrored airfoil configuration inspired by an energy-harvester

A novel wind energy harvesting system has recently been designed to capture distributed wind energy. This design abandons the traditional turbine design that is standard for wind energy, and instead adopts two mirrored airfoils and extracts energy from the low pressure region between the foils. During experimental testing, the system showed high potential, with an increase in harvesting capacity as the angle-of-attack of the airfoils increased. This benefit, however, disappeared for sufficiently high angle-of-attack, commensurate with a shift from a symmetric to a directed wake. To investigate this detrimental transition, we present here simulations for the mirrored airfoil configuration at a Reynolds Number of 1000. Using this data, we provide a regime map that conveys the system dynamics for a sweep of the angle-of-attack and spacing between the mirrored airfoils. Our results indicate that the transition to the asymmetric wake is due to a linear instability—absent in the single airfoil case—that is due to the aerodynamic coupling of the foils. We explore this instability mechanism using detailed analysis of the time-varying flow-field and comment on potential implications on harvesting potential for this wind energy system.