Wake-foil interactions and energy harvesting efficiency in tandem oscillating foils

Oscillating foils in synchronized pitch and heave motion can harvest hydrokinetic energy while leaving behind a distinct trail of alternating signed vortices. This work correlates the specific foil kinematics (frequency, pitch, and heave amplitude) with the resulting wake structure by defining three modes within the energy harvesting kinematic regime. Using an array of two tandem oscillating foils, the performance of the trailing foil is modeled by analyzing the wake between the two oscillating foils. The resulting efficiency of the trailing foil is redefined by accounting for the steady and unsteady components of the local flow, yielding a closer match to the single foil efficiency curve.