A time-varying formulation of the curled wake model within the FAST.Farm framework

In this article, we present a time-varying formulation of the curled wake model that we implemented in FAST.Farm. The curled wake model, originally developed for steady-state conditions, is used to produce realistic wake profiles behind a wind turbine in yawed (or skewed) conditions. We begin by introducing the key elements of the FAST.Farm framework. Then, after briefly summarizing the original wake dynamics formulation of FAST.Farm based on a polar wake profile, we present the new time-varying formulation of the curled wake model, compare the two, and highlight the differences with the original curled wake model. After discussing some implementation details, we present different applications with increasing levels of complexity: single turbine with uniform and turbulent inflow, fixed and transient yaw, and multiple turbines. We verify our results using the original FAST.Farm implementation and large-eddy simulations. The results with the new curled wake model are improved compared to the original implementation, as they include cross-flow velocities and wake asymmetry. Yet, large-eddy simulation results show a more pronounced lateral convection of the wake and a stronger concentration of vorticity at the top vortex. The new curled wake implementation in FAST.Farm should enable the calculation of not only generator power but also wind turbine structural loads for applications involving intentional or unintentional skewed flow and wind-farm control involving wake steering.