The wake of an actuator line with a vortex-based tip/smearing correction in uniform and turbulent inflow

Abstract

The force smearing in the actuator line technique ensures its numerical stability, but also breaks its intended similarity to the lifting line by similarly smearing its vorticity in the flow domain. The wake thus induces lower velocities at the blade, linking the blade forces to the force smearing. A recently developed tuning-free, vortex-based correction recovers this missing induction, regaining the lifting-line behaviour of the actuator line. The interplay of this new smearing correction with grid and blade resolution is studied in uniform and turbulent inflow with respect to the blade forces and wake behaviour. With only 10 grid cells along the blade, the thrust is within 2.8% and the power within 5.7% of the high-resolution reference. With 20 grid cells the difference drops to 1.5% and 2.5%, respectively. The influence of the force smearing on the wake velocities dominates over the choice of correction, yet under turbulent inflow the wake characteristics become nearly independent of force smearing 6 rotor radii downstream of the turbine.