Influence of Bilateral WIG Effect on Oscillating Hydrofoil Energy Harvesting Performance and Experimental Suggestions

The oscillating hydrofoil represents a promising tidal energy harvesting device, but its hydrodynamic behavior and energy harvesting performance can be significantly affected by the wing-in-ground (WIG) effect under near-wall conditions. The present work establishes a two-dimensional numerical model that accounts for bilateral WIG effect to investigate the effect of three key parameters, namely the dimensionless wall distance (H∗), the Reynolds number (Re), and the reduced oscillation frequency (f∗) on energy harvesting performance. The formation, shedding, and reattachment of the leading-edge vortex (LEV) are analyzed to clarify the underlying hydrodynamic mechanisms. The results demonstrate that the WIG effect notably enhances the energy harvesting efficiency of the oscillating hydrofoil. At Re=5×105 and f∗=0.14, the maximum energy harvesting efficiency reaches 69.6% at H∗=2, representing an improvement of 84.1% over the reference efficiency of 37.8% at the negligible WIG reference condition of H∗=40. As H∗ increases, the hydrodynamic performance gradually approaches that of the unconfined hydrofoil. Based on the predefined 5% efficiency-deviation criterion, the WIG effect becomes negligible at approximately H∗=9. The sensitivity to the WIG effect increases at higher oscillation frequencies, whereas its dependence on Re is non-monotonic, decreasing up to Re=4.5×105 and increasing thereafter. Finally, the four-component Gaussian mixture model (GMM) is employed to construct a prediction model for the wall distance at which the WIG effect becomes negligible under different combinations of the Reynolds number and the oscillation frequency. The model achieves an RMSE of 1.991 and an R2 of 0.667. These results quantify the effective range of the bilateral WIG effect and provide a practical criterion for reducing wall interference in relevant experiments.