Unsteady aerodynamic loads and wake dynamics of twin floating vertical axis wind turbines under asynchronous phase rolling excitation

The operational phase difference between twin floating vertical axis wind turbines (FVAWT) serves as a key variable in regulating their asynchronous motion patterns, directly influencing the strength of aerodynamic interference and the coupled behavior of wake structures. A high-fidelity computational fluid dynamics (CFD) model is developed based on overlapping and dynamic grid techniques, in which customized motion functions are implemented to actively impose rolling motions and asynchronous phase control. The accuracy of the numerical model is systematically validated against wind tunnel experiments. The results show that the phase difference significantly regulates energy capture and load response. Under the π/2 phase, the power coefficient (CP) reaches 0.396, which is an increase in 10.4% and 21.8% compared to the in-phase (0 phase) and fixed twin FVAWTs configurations, respectively. The asymmetric wake interference and dual-frequency vortex structures induced by this phase difference lead to the highest near-field recovery capability. In contrast, the cooperative wake pairing observed under 0 phase enhances far-field velocity recovery, with a recovery ratio of 0.927 at 10D (VAWT diameter). However, this configuration also leads to larger lateral force (Fy) fluctuations. The CP under the π phase is at a moderate level, with the backward displacement of the wake and the lateral momentum cancelation mechanism demonstrating optimal lateral disturbance control. This results in the minimum Fy coefficient (CFy), which is 0.034. The phase difference reveals the complex coupling relationship between asynchronous excitation and shear layer reconstruction.