A Lightweight Vortex Particle-Mesh Library for Variable-Fidelity Simulation of Wind Turbine Wakes

Abstract. In this work, the implementation and validation of a lightweight vortex-particle mesh solver is described. Within this method, the flow field is discretised with vorticity-carrying Lagrangian particles. Field quantities are calculated on a homogeneous rectangular grid and mapped to the instantaneous particle positions. A fast Poisson solver is employed to efficiently calculate the velocity field on the grid using fast Fourier transforms. The vorticity field is updated by applying the vorticity transport equation, the terms of which are extracted from the flow field using finite differences. The flow solver is validated by simulating an unsteady vortex ring. A nested grid region is generated which allows for the flow field representation of lift-generating bodies on the main grid. This secondary grid approach allows for the use of arbitrary lifting body models. Here, a nonlinear lifting line method has been applied and validated against an analytical solutions for an elliptical wing. The solver is validated for helical wake configurations through comparison with an idealized Betz rotor. Finally, the application to the simulation of wind turbine wakes is demonstrated through comparison with experimental results of rotor loads and wake hot-wire measurements performed in the Mexico wind tunnel campaign.