Advanced medium-order modelling for the prediction of the three-dimensional wake shed by a vertical axis wind turbine

A recently formulated model for the treatment of the evolution of the wake of aerodynamic bodies has been implementedinto the wind turbine simulation software QBlade with the aim ofmodelling near and far wake behavior with a so-called mediumorder model. The paper first presents the vortex particle treatment of the wake. Shed and trailing vortex elements generatedby a lifting line model of the turbine blade are allowed to freelyconvect under the action of the freestream, body and wake influence. Induced velocities are calculated with use of a regularizedBiot-Savart kernel. The method is validated against experimentscarried out in the large-scale wind tunnel of the Politecnico diMilano on a H-type turbine architecture. Wake velocities and periodic unsteadiness are predicted relatively well by the methodfor two tip speed ratios. It is observed that higher order effects such as vortex stretching and viscous interaction must beimplemented into the model in order to accurately predict wakeevolution. A recently developed vortex particle multilevel multiintegration method has been implemented which approximatesthe far-field influence of the particles and reduces significantlythe computational expense. The paper also reports on the implementation of higher order effects into this optimization framework to account for evolution of vortex particle strength and theinclusion of viscous effects into the model, which are shown to beparticularly relevant for vertical axis wind turbines.