Validation and accommodation of vortex wake codes for wind turbine design load calculations

Abstract

Abstract. The computational effort for wind turbine design loads calculations is more extreme than it is for other applications (e.g. aerospace) which necessitates the use of efficient but low-fidelity models. Traditionally the Blade Element Momentum (BEM) method is used to resolve the rotor aerodynamics loads for this purpose, as this method is fast and robust. With the current trend of increasing rotor size, and consequently large and flexible blades, a need has risen for a more accurate prediction of rotor aerodynamics. Previous work has demonstrated large improvement potential in terms of fatigue load predictions using vortex wake models together with a manageable penalty in computational effort. The present publication has contributed towards making vortex wake models ready for application to certification load calculations. The observed reduction in flapwise blade root moment fatigue loading using vortex wake models instead of the Blade Element Momentum method from previous publications has been verified using a numerical wind tunnel, i.e. Computational Fluid Dynamics (CFD) simulations. A validation effort against a long term field measurement campaign featuring 2.5 MW turbines has also confirmed the improved prediction of unsteady load characteristics by vortex wake models against BEM based models in terms of fatigue loading. New light has been shed on the cause for the observed differences and several model improvements have been developed, both to reduce the computational effort of vortex wake simulations and to make BEM models more accurate. Scoping analyses for an entire fatigue load set have revealed the overall fatigue reduction may be up to 5 % for the AVATAR 10 MW rotor using a vortex wake rather than a BEM based code.

Utilizing high fidelity data into engineering model calculations for accurate wind turbine performance and load assessments under design load cases

“…The code has been improved over the time accommodating several latest development in the field, for example, better handling of the polar gradient for dynamic stall modeling, the inclusion of the structural velocity in induction calculations, improved calculation speed and integrated wind turbine aero-structural offshore platform analyses. Several publications documented verification studies of the Bladed code performance [32,[43][44][45][46][47][48][49][50].…”

“…The basic theory of the implementation strategy was described by Kloosterman [54]. The following works documented the performance of the Bladed Vortexline model [45,46,55,56]. The code is run in parallel and adopts vectorized implementation to accelerate the running time.…”

“…For the turbulent case, a high turbulence intensity was defined to fully explore the influence of turbulence on a large wind turbine rotor. The CFD simulations presented in this section were submitted to the Vortex Loads project [45] as the contribution of the University of Stuttgart. Engineering model simulations were computed by utilizing BEM and Vortexline approaches by adopting standard polar data and the synthesized 3D CFD polar data described in Section 2.3.…”

Characterization of the unsteady aerodynamic response of a floating offshore wind turbine

“…The ECN Aero-Module (Boorsma et al, 2011(Boorsma et al, , 2016(Boorsma et al, , 2020 contains two aerodynamic models, namely the Blade Element Momentum (BEM) method similar to the implementation in PHATAS (Lindenburg and Schepers, 2000) and a free vortex https://doi.org/10.5194/wes-2020-94 Preprint. Discussion started: 11 August 2020 c Author(s) 2020.…”

Challenges in Rotor Aerodynamic Modeling for Non-Uniform Inflow Conditions

“…For non-uniform inflow conditions such as turbulent inflow, which is prescribed for fatigue load simulations, it has been less straightforward to achieve satisfactory agreement between simulations themselves [10,11], as well as between predictions and measurements. At the same time, upscaling of wind turbine rotors has made these inflow non-uniformities (e.g.…”