The objective of this project is to enable scalable arrays of damless oscillating hydrofoil turbines that will offer higher efficiencies, higher power output levels, and wider applicability than current hydropower technologies. The proposed work will take advantage of unique, recently uncovered wake-structure interactions that can increase power output and efficiency in densely packed arrays of oscillators. The approach of using oscillating hydrofoil devices that can be closely arranged together will open new markets for hydropower in locations previously considered too shallow or cluttered to be feasible. With many population centers located on coastlines and along rivers, this new source of clean energy would have minimal transmission costs and losses. Such devices could also be invaluable in off-grid sites like remote villages or temporary shelters for people displaced by disasters. Smaller scale applications could create flow-powered sensing stations that do not rely on short-term and environmentally hazardous consumable batteries for applications like monitoring critical infrastructure. At the utility grid scale, when compared to other renewable energy sources like wind and solar power, oscillating turbine hydrokinetic power arrays will offer more convenient integration into the power grid due to the predictable nature of the energy source. While wind and solar power are subject to daily variation and intermittency due to weather changes, tidal flows in particular can be accurately predicted well in advance, allowing the various sources in the utility grid to be readily balanced to cost-effectively meet demand and production allocations. In addition, the proposed education activities will serve to help broaden participation in engineering and inspire children to Science, Technology, Engineering, and Math (STEM) studies. North Carolina middle school and junior high school students will learn about flow energy harvesting and engineering design in a hands-on lab activity the researchers will develop and run as part of the popular NC State University summer camp program. The researchers will also broaden participation in research by providing opportunities for underrepresented undergraduate students from public colleges across North Carolina to engage in mentored research activities in the PI's and Co-PI's labs.
Unlike traditional spinning turbines, which must be widely spaced to perform most effectively, our preliminary experiments have shown that oscillating energy harvesting devices actually perform most effectively when they are closely packed together and their motions become coupled by the wake flow. This work will determine how arrays of oscillating turbines can be modeled, controlled, and optimally configured to take advantage of these synergistic interactions between the wakes of upstream and downstream devices. Current wind and hydrokinetic energy research largely focus on the performance of individual devices from a mechanical or fluid dynamics standpoint, or the interaction and combination of power sources in a "smart grid" from an electrical perspective. The work proposed will leverage a different approach that exploits and optimizes interactions between devices at the mechanics level. Specifically, experimental and analytic studies will (1) investigate the parameters that govern the occurrence, strength, and scaling of the synergistic wake-structure coupling and how it can be used to enhance the performance of 2D arrays of hydropower energy harvesters. The researchers will also (2) quantitatively compare active, passive, and hybrid actuation and control approaches for the oscillating turbines, and (3) quantify the influence of the shallowness of the water body on the wake structure formation of individual and collective energy harvesters.
