Impacts of blade designs on wake dynamics in tandem wind turbine configurations

This study investigates the impacts of blade aerodynamic design, specifically the spanwise distribution of axial force, on the wake dynamics in tandem turbine configurations. Using large-eddy simulations with actuator surface models, we analyse five tandem set-ups comprising three blade designs: a baseline (NREL-Ori), a root-loaded (NREL-Root) and a tip-loaded (NREL-Tip) variant. Two scenarios are examined: one varying the downstream design with a baseline upstream turbine (scenario I), and another varying the upstream design with a baseline downstream turbine (scenario II). Results show that blade designs significantly affect wake behaviours in both scenarios. In scenario I, the root-loaded design exhibits a larger near-wake velocity deficit but recovers faster due to intensified shear layer instability, which is similar to that observed for a stand-alone turbine. In scenario II, the upstream blade design significantly influences the downstream turbine, with the root-loaded design prematurely triggering wake meandering and accelerating downstream flow recovery. Energy spectra and spectral proper orthogonal decomposition reveal a frequency-selection mechanism linking the strength of the near-wake shear layer, which can be controlled by blade design and inflow structure, to wake evolution. Specifically, the downstream wake resonates with the upstream wake, particularly at the meandering frequency. These resonant behaviours are qualitatively similar across the considered two-turbine configurations. However, the onset location and the intensity of such behaviours depend on the blade designs and their streamwise arrangement. These findings highlight the possibility of optimising blade designs for improving turbine array performance.