6 | SIMPACK News | November 2009

CuStoMer APPlICAtIon | Florian Stache, Birte-Marie Ehlers, Suzlon Energy GmbH

ABout Suzlon enerGYSuzlon ranks as the world’s fifth leading wind turbine manufacturer with over 10.5 % of global market share in 2007. The company has been the leading manufacturer in the Indian market for nine consecutive years, maintaining over 50% market share. Suzlon has its head quarters in Pune, India. The company’s global profile is reflected in its project and market portfolio — extending across Asia, Australia, Europe and North and South America. Product development is based in Germany.

lIMItAtIonS oF SIMulAtIon CoDeSMost of the aeroelastic codes in use for daily wind turbine design are based on the Blade Element Momentum Theory (BEM) which enables the use of turbulent 3D wind fields.Codes like FLEX5 were developed in the early 1990's and, since then, have been continuously improved and adapted to the needs of specific wind turbine designers.

and frequency domain can be made with almost no restrictions in the number of degrees of freedom used. Wind turbine manufacturers and certification bodies are using multi-body simulations more and more. Investigations of the wind turbines and their components can be made in an ever increasing level of detail. For example, drive trains which include high frequency dynamics can be analysed precisely. Furthermore, non-linearities in the pitch and yaw systems or vibration problems of different structural components can be thoroughly investigated.

trAnSFer oF FleX5 to SIMPACKIn order to work with a validated base, the first step towards the initiation of SIMPACK models at Suzlon was to have an aeroelastic simulation which produces the same results as the FLEX5 model. For these comparisons, models with similar levels of fidelity have been used.

Their main advantages remain in easy handling and high computational efficiency. The reliability of the produced results has been proven through several verifications by measurements and other codes. Use within the day to day wind turbine design process,

including certification, validates the confidence placed in these tools. As for FLEX5, the source code is freely accessible — improvements in the

control, generator or even aerodynamic routines can be implemented. However, for such enhancements, a thorough understanding of the code is necessary.In FLEX5 the number of degrees of freedom is limited to 28 and cannot be increased without performing a huge modification of the code structure.

ADVAntAGeS oF SIMPACKSIMPACK offers a simulation environment in which mechanical systems can be modelled comfortably. Analyses in the time domain

Short product development cycles and limited testing possibilities are driving the need for full system simulation in the wind energy sector. Years of simulation experience has won users' confidence in FleX5 for load calculations. nevertheless, the development of more advanced models using general multi-body simulation codes like SIMPACK is required. Suzlon energy is combining the advantages of both worlds.

“SIMPACK offers a simulation environment in which

mechanical systems can be modelled comfortably”

Fig. 1: Flex5 aerodynamic code

Fig. 2: SUZLON S88 wind turbine

Wind turbine Aeroelastic Simulationby embedding FleX5 into SIMPACK

SIMPACK News | November 2009 | 7

Florian Stache, Birte-Marie Ehlers, Suzlon Energy GmbH | CuStoMer APPlICAtIon

The established FLEX5 models of the Suzlon wind turbines have been validated with good correlation to measurements and successful certifications of the turbines.The concept behind the transfer of the FLEX5 model to SIMPACK relies on using the flexible body and kinematic measurements functionality of SIMPACK. The aerodynamic routines and additional interface routines are cut out of FLEX5 and are encapsulated into a Dynamic Link Library (dll) which is called from a SIMPACK user routine. The blade element positions and velocities are read out of SIMPACK and handed over to the aerodynamic routine. The configuration of this routine is described in Fig. 1. All mechanical calculations, e. g. the evaluation of the position and speed of the given blade element, the evaluation of inertia terms and transformation into modal coordinates, were removed from the FLEX5 code. Only the remaining aerodynamic terms are inserted into SIMPACK.For this study Suzlon transferred the FLEX5 model of the S88 wind turbine (Fig. 2) into an entire SIMPACK simulation. Fig. 3 illustrates the animated SIMPACK model with aerodynamic forces acting on the flexible rotor blades.

reSultS AnD teStInGIn order to verify the calculated results, a SIMPACK model with the same degrees of freedom as in the FLEX5 model was set up. The control and generator behaviour was considered in SIMPACK using either user routines or interfaces to MATLAB/

Simulink models. Finally the resulting load calculations of the SIMPACK time integration and the resulting time series of FLEX5 were compared directly within the SIMPACK post-processor. The testing experiment was run for a load case with a constant wind of 12 m/s for a Suzlon S88 2.1 MW wind turbine. Fig. 4 shows the SIMPACK/FLEX5 comparison of the electrical power and the magnitude of the tower bottom moments (MB). Fig. 5 presents both the blade root moments flapwise (MY) and edgewise (MZ) for SIMPACK and FLEX5. The calculated moments of the new SIMPACK model show good correlation to the time series of the validated FLEX5 model.

ConCluSIonThe results of the presented SIMPACK model show good correlation to the

Fig. 3: SIMPACK model of Suzlon wind turbine with aerodynamic forces acting on flexible rotor blades

Fig. 4: Comparison of SIMPACK and FLEX5 time series for the electrical power and the magnitude of the tower bottom moment.

Fig. 5: Comparison of SIMPACK and FLEX5 time series for the blade root moments MY and MZ

validated FLEX5 model and give evidence that the development of SIMPACK multi-body simulation models (with increasing complexity and elimination of the need

to perform time consuming aeroelastic field validation) is possible for Suzlon.Future models vary

in the number of degrees of freedom and can include detailed submodels of various components of wind turbines. Component assemblies such as the pitch system or the gearbox, and further structural components like the main frame, can be incorporated into the simulation. This allows a more thorough understanding of their influence on the global wind turbine loads and the generation of more precise loads for the analysis of single components.

“...results of the SIMPACK model show good correlation to the

validated FLEX5 model...”