An actuator-line model with Lagrangian-averaged velocity sampling and piecewise projection for wind turbine simulations

A new approach is proposed to do the velocity sampling for actuator-line models (ALM). Unlike the conventional spatial averaging approaches, the velocity sampling is performed in a Lagrangian averaging way along flow paths with a time scale depending on the local flow patterns. The new approach is evaluated by large-eddy simulations of a utility-scale National Renewable Energy Laboratory (NREL)-5MW wind turbine. The results show that the Lagrangian approach of velocity sampling is effective to reduce the spurious numerical oscillations in the modeling results. The good match with the benchmark data indicates that correct free upwind velocity can be obtained with a careful determination of the associated time scale. Also, a piecewise function is proposed to replace the Gaussian function for the force projection process.