Collaborative Research: Structured wakes behind oscillating foils: characterization, control, and cooperative behavior

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Energy harvesting using oscillating foils has the potential to tap large hydrokinetic (tidal and riverine) energy resources and provide renewable and sustainable energy to water-front communities. Oscillating foils are less harmful to marine flora and fauna, can operate in many more locations and at lower water speeds than is possible for conventional rotary hydrokinetic turbines. Oscillating foils can also be placed in close proximity to each other, increasing the power density - the total power that can be extracted from a given area. However, optimizing this placement depends on improved understanding of the interactions between adjacent hydrofoils, and in particular, the way in which structured wakes form, advect downstream and impact the performance of a neighboring hydrofoil. This research project will address these issues, and lead to the development of predictive tools that can aid in the development of commercially feasible hydrokinetic energy systems, Using a tightly-integrated combination of experimental and computational approaches, a systematic framework will be developed for systematically characterizing and controlling the wake interactions between oscillating foils. The primary goal is to categorize vortex topology & convective paths based on the kinematics of the flapping motion. These tools will be developed with aid of machine learning classification and regression models. Once the wake structure is well-predicted, control algorithms will be developed, and the vortex-foil interactions will be characterized in terms of beneficial and detrimental interactions for the purpose of energy harvesting. Simulations of single and multiple hydrofoils will be performed using a combination of two-dimensional direct numerical simulation (DNS) and three-dimensional Large Eddy Simulations (LES). A computer-controlled three-hydrofoil system each equipped with force and torque sensors will be used in a large open surface water flume in conjunction with unsteady wake velocity surveys using Particle Image Velocimetry (PIV).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.