Modeling energy extraction in dual oscillating foil turbines

This talk presents a model to predict the energy extraction of dual oscillating foil, marine energy, turbines. Oscillating foils extract hydrokinetic energy from free-stream flows through a combination of periodic heave and pitch motions at relatively higher amplitudes and lower reduced frequency than thrust generating foils. Individual oscillating foils can operate at efficiencies of approximately 30%, however multiple turbines operating in close proximity of one another can further improve energy density and system efficiency. Oscillating foils are unique in that their wake exhibits strong coherent vortices with the potential for constructive vortex-foil interaction. However, simulations examining all system parameters in multi-foil arrays (flapping kinematics and foil placement) are computationally exhaustive, and thus a simpler analytical model is presented to aid with array design and optimization. This work utilizes performance and wake-extracted data from single-foil simulations to model the energy harvesting performance of foils placed downstream. The algorithm predicts the power generation of the second foil through the mean and unsteady wake characteristics, including the direct impingement of a vortex with the trailing foil. As a result, the second foil time-dependent power curve is successfully reconstructed as a function of downstream foil placement, phase angle, and kinematic stroke parameters.