Large-eddy simulation of shear-driven wake interactions in tandem wind turbines

The role of inflow shear in wind-turbine wake dynamics remains poorly understood, since it is difficult to disentangle shear effects from atmospheric turbulence in experimental and operational settings. In this work, high-fidelity large-eddy simulations with over 100 million grid cells, coupled with the actuator line method, are employed to investigate wake interactions between two aligned NREL-5MW turbines. To isolate shear-driven mechanisms in isolation from background turbulence effects, the study deliberately avoids modeling a fully developed atmospheric boundary layer and instead imposes controlled linear vertical shear profiles at the inlet. These profiles are derived from the classical power-law formulation while maintaining a fixed hub-height velocity across all simulations. The results show three primary effects of vertical shear: shear destabilizes the tip-vortex system, enhances turbulence production and streamwise Reynolds stresses, and imprints a persistent vertical asymmetry in the wake. Collectively, these effects accelerate wake recovery and substantially modify the inflow to the downstream turbine, resulting in increased power output (up to 11%) coupled with enhanced cyclic loading. These findings establish that vertical shear, independent of background turbulence, is a primary determinant of wake recovery and downstream turbine performance, with direct implications for high-fidelity wake modeling and wind-farm optimization.