Original Article Aeroservoelastic simulations for horizontal axis wind turbines CS Prasad 1 , Q-Z Chen 1 , O Bruls 1 , F D’Ambrosio 2 and G Dimitriadis 1 Abstract This paper describes the development of a complete methodology for the aeroservoelastic modelling of horizontal axis wind turbines at the conceptual design stage. The methodology is based on the implementation of unsteady aerodynamic modelling, advanced description of the control system and nonlinear finite element calculations in the Samcef Wind Turbines design package. The aerodynamic modelling is carried out by means of fast techniques, such as the blade element method and the unsteady vortex lattice method, including a free wake model. The complete model also includes a description of a doubly fed induction generator and its control system for variable speed operation. The Samcef Wind Turbines software features a nonlinear finite element solver with multi-body dynamics capability. The full methodology is used to perform complete aeroservoelastic simulations of a realistic 2 MW wind turbine model. The interaction between the three components of the approach is carefully analysed and presented here. Keywords Horizontal axis wind turbines, aeroservoelasticity, nonlinear finite elements, unsteady vortex lattice method, doubly fed induction generator Date received: 12 May 2016; accepted: 13 October 2016 Introduction Horizontal axis wind turbines (HAWT) are one of the most popular machines for producing renewable energy in the world. Over the last two decades, a sig- nificant shift in government policy towards renewable energy has led to bigger and more efficient wind tur- bines, a development that has stretched the capabil- ities of traditional wind turbine design methods. High fidelity and integrated multidisciplinary models of wind turbine systems are important for the correct evaluation of the performance and the load analysis, and thus might reduce the failure rate during the design stage. This has in turn led to a need for more advanced design tools that can model the complete wind turbine, including nonlinear structural and con- trol effects as well as unsteady aerodynamic flows around the rotor. For example, holistic finite element approaches for the analysis of wind turbines are described by Bottasso et al. 1 and Heege et al. 2 Higher fidelity aeroservoelastic simulation of com- plete wind turbine models is the main focus of the present work. In 2006, Hansen et al. 3 published an authoritative review of wind turbine aerodynamic and aeroelastic modelling approaches; however, the practical application of such methods has lagged behind. The aerodynamic modelling of wind turbines at the con- ceptual design stage is usually carried out by means of the blade element momentum (BEM) approach. This technique is very efficient but is based on quasi-steady aerodynamic assumptions. It can model flow separ- ation but only in a quasi-steady manner; furthermore, it does not model the wake behind the wind turbine. An alternative unsteady aerodynamic modelling tech- nique is the vortex lattice method (VLM) 4,5 that was first applied to wind turbines in the 1980s. It models a lifting surface and the wake shed behind it as a con- tinuous vortex surface. Its main limitation is that the flow is assumed to be always attached. Higher fidelity panel methods can model flow separation through viscous–inviscid interaction coupling. 6,7 Clearly, no 1 Aerospace and Mechanical Engineering Department, University of Lie `ge, Belgium 2 Siemens PLM Software, LMS Samtech, Lie `ge Science Park, Lie `ge, Belgium Corresponding author: G Dimitriadis, Universite de Liege, Quartier Polytech 1, Allee de la Decouverte 9, Liege 4000, Belgium. Email: gdimitriadis@ulg.ac.be Proc IMechE Part A: J Power and Energy 2017, Vol. 231(2) 103–117 ! IMechE 2016 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0957650916678725 journals.sagepub.com/home/pia