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

TL;DR

This study investigates wake-foil interactions in tandem oscillating foils to optimize energy harvesting efficiency by analyzing wake structures, developing predictive models, and identifying regimes that enhance array performance.

Contribution

It introduces a comprehensive wake analysis linking foil kinematics to wake characteristics and proposes a predictive wake model for improved energy harvesting in tandem arrays.

Findings

Identified three wake regimes affecting efficiency.

Quantified mean velocity and turbulent kinetic energy in wakes.

Developed a wake model to predict foil array performance.

Abstract

Oscillating foils in synchronized pitch/heave motions can be used to harvest hydrokinetic energy. By understanding the wake structure and its correlation with the foil kinematics, predictive models for how foils can operate in array configurations can be developed. To establish a relationship between foil kinematics and wake characteristics, a wide range of kinematics is explored in a two-foil tandem configuration with interfoil spacing from four to nine chord lengths separation and multiple interfoil phases. Using data from experiments and simulations, an in-depth wake analysis is performed and the mean velocity and the turbulent kinetic energy are quantified in the wake. With this energy quantification, the trailing foil efficiency is modified to account for the mean flow in addition to the energy transported by the coherent leading edge vortices (LEVs) shed from the leading foil. With the mean wake velocity, a predictive wake model is able to distinguish three regimes through analyzing trailing foil efficiency profiles and the strength of the primary LEV shed from the leading foil. Dividing the wake into regimes is an insightful way to narrow the range of foil kinematics and configurations and improve the energy harvesting in a two-tandem foil array.