ViVonBlades: Vortex-induced vibrations on wind turbine rotor blades

At a glance

• Vortex-induced vibrations (ViV), which develop on rotor blades, can cause the entire wind turbine to vibrate, posing a risk of damage and accidents.
• To date, the simplified methods applied in rotor blade design are not adequate for the reliable calculation of ViV. As a result, findings regarding ViV only become apparent late in the design or production process and may require revision of the rotor blade design.
• In the ViVonBlades research project, the project partners are investigating the potential of fully resolved fluid-structure interaction (FSI) simulations, with the aim of achieving reliable results in the calculation of ViV.
• Fraunhofer IWES is responsible among other tasks for the design and performance of the FSI simulations required for this purpose.

The challenge

ViV are triggered by vortex shedding on wind turbine rotor blades and cause not only the blades but also the entire wind turbine to vibrate. The consequences are immense: the vibrations put the operating stability, structural integrity, and thus the structural stability of the wind turbine in jeopardy. This problem becomes more critical as blade sizes increase.

To date, it is scarcely possible to take ViV into consideration in the early phases of rotor blade design. The applied blade element momentum (BEM) theory methods utilize polar look-up tables and dynamic stall models to estimate the aerodynamics, which are not able to capture the unsteady aerodynamics associated with ViV completely. Consequently, the effects of the vortex-induced vibrations are only recognized at a late stage in the rotor blade development process. This may result in the entire design needing to be revised, which leads to delays and high costs.

The solution

This is where the ViVonBlades research project comes in. The aim is to be able to calculate the force distribution of vortex shedding reliably using fully resolved CFD (computational fluid dynamics) simulations. To this end, the project partners are evaluating available methods for turbine design: a series of FSI simulations, designed and performed at Fraunhofer IWES, is being compared with unidirectionally coupled simulations with imposed blade deformations as well as with an engineering model.

In addition, Fraunhofer IWES will be responsible for the investigation of turbulence models used in the flow simulation as well as for the validation and evaluation of the different methods often employed in the early design phases for the blade structure calculations.

The added value

ViVonBlades will help to evaluate and improve the models employed to calculate vortex-induced vibrations and the reliability of their results. Greater confidence in the calculations and predictions of ViV phenomena in the preliminary rotor blade design stages can help to avoid high redesign costs in the final design stages and in the production phase.