A Prescribed-Wake Vortex Line Method for Aerodynamic Analysis and Optimization of Multi-Rotor Wind Turbines

This paper extends the prescribed wake vortex lattice/line method (VLM) to perform aerodynamic analysis and optimization of dual-rotor wind turbines (DRWTs). A DRWT turbine consists of a large, primary rotor placed co-axially behind a smaller, secondary rotor. The additional vortex system introduced by the secondary rotor of a DRWT is modeled while taking into account the singularities that occur when the trailing vortices from the secondary (upstream) rotor interact with the bound vortices of the main (downstream) rotor. Pseudo-steady assumption is invoked and averaging over multiple relative rotor positions is performed to account for the primary and secondary rotors operating at different rotational velocities. Our implementation of the VLM is first validated against experiments and blade element momentum theory results for a conventional, single rotor turbine. The solver is then verified against Reynolds Averaged Navier-Stokes (RANS) CFD results for two DRWTs. Parametric sweeps are performed using the proposed VLM algorithm to optimize a DRWT design. The problem with the algorithm at high loading conditions is highlighted and a solution is proposed that uses RANS CFD results to calibrate the VLM model. ∗Corresponding author Email addresses: [email protected] (Aaron Rosenberg), [email protected] (Anupam Sharma) Preprint submitted to NAWEA Symposium June 5, 2015