Effect of order of accuracy of fluid-structure-interaction algorithms on actuator-line simulations of wind turbines

Actuator-line simulations of wind turbines often use loose coupling for the fluid-structure interaction (FSI) algorithm that reduces the numerical order of accuracy of fluid and structural solver. Demonstrating expected convergence rates with spatial- and temporal-grid refinement is the ``gold standard'' of code and algorithm verification. With increasing size and flexibility of modern wind turbines, the order of accuracy of the FSI algorithm could also play a major role in the prediction of coupled unsteady aerodynamic effects. In this work, we demonstrate that a new FSI algorithm is second-order accurate using the method of manufactured solutions for actuator-line CFD simulations with a simplified structural model. We then implement the same FSI algorithm for actuator-line simulations coupled to the multi-physics OpenFAST wind turbine simulation tool. We demonstrate the effects of the order of accuracy of the FSI algorithm on simulations of wind turbines in a wind farm.