Benchmark of a Novel Aero-Elastic Simulation Code for Small Scale VAWT Analysis

Abstract

After almost 20 years of absence from research agendas, interest in the vertical axis wind turbine (VAWT) technology is presently increasing again, after the research stalled in the mid 90’s in favour of horizontal axis turbines (HAWTs). However, due to the lack of research in past years, there are a significantly lower number of design and certification tools available, many of which are underdeveloped if compared to the corresponding tools for HAWTs. To partially fulfil this gap, a structural FEA model, based on the Open Source multi-physics library PROJECT::CHRONO, was recently integrated with the Lifting Line Free Vortex Wake method inside the Open Source wind turbine simulation code QBlade and validated against numerical and experimental data of the SANDIA 34m rotor. In this work some details about the newly implemented nonlinear structural model and its coupling to the aerodynamic solver are first given. Then, in a continuous effort to assess its accuracy, the code capabilities were here tested on a small scale, fast-spinning (up to 450 rpm) VAWT. The study turbine is a helix shaped, 1kW Darrieus turbine, for which other numerical analyses were available from a previous study, including the results coming from both a 1D beam element model and a more sophisticated shell element model. The resulting data represented an excellent basis for comparison and validation of the new aero-elastic coupling in QBlade. Based on the structural and aerodynamic data of the study turbine, an aero-elastic model was then constructed. A purely aerodynamic comparison to experimental data and a BEM simulation represented the benchmark for QBlade aerodynamic performance. Then, a purely structural analysis was carried out and compared to the numerical results from the former. After the code validation, an aero-elastically coupled simulation of a rotor self-start has been performed to demonstrate the capabilities of the newly developed model to predict the highly nonlinear transient aerodynamic and structural rotor response.