Abstract
Abstract. The actuator line (AL) was intended as a lifting line (LL) technique for computational fluid dynamics (CFD) applications. In this paper we prove – theoretically and practically – that smearing the forces of the actuator line in the flow domain forms a viscous core in the bound and shed vorticity of the line. By combining a near-wake representation of the trailed vorticity with a viscous vortex core model, the missing induction from the smeared velocity is recovered. This novel dynamic smearing correction is verified for basic wing test cases and rotor simulations of a multimegawatt turbine. The latter cover the entire operational wind speed range as well as yaw, strong turbulence and pitch step cases. The correction is validated with lifting line simulations with and without viscous core, which are representative of an actuator line without and with smearing correction, respectively. The dynamic smearing correction makes the actuator line effectively act as a lifting line, as it was originally intended.
Highlights
The correction is validated with lifting line simulations with and without viscous core, which are representative of an actuator line without and with smearing correction, respectively
The actuator line (AL) technique developed by Sørensen and Shen (2002) is a lifting line (LL) representation of the wind turbine rotor suitable for computational fluid dynamics (CFD) simulations
The actuator line was intended as a lifting line technique for CFD applications
Summary
The actuator line (AL) technique developed by Sørensen and Shen (2002) is a lifting line (LL) representation of the wind turbine rotor suitable for computational fluid dynamics (CFD) simulations. As actuator disc formulations suffer from similar issues towards the blade tip, Glauert (1935) type tip corrections are frequently applied to ALs (Shen et al, 2005) These correct discs for missing discrete blades and should be unnecessary – strictly even invalid – for ALs. Shives and Crawford (2013) and Jha et al (2014) achieved a reduction in the force over-prediction by varying the originally fixed smearing factor with respect to the blade chord Their methods cannot decouple the blade forces from the smearing length scale: a smeared force distribution in the flow domain unavoidably leads to lower induction at the blade – increasing lift and drag – compared with an actual LL with a concentrated, spatially singular force
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