Response of Stall Regulated Wind Turbines - Stall Induced Vibrations: Final report on FOULE 1 contract no. FOUR-0076 for the Commission of the European Communities, Directorate General XII for Science, Research and Development

The fear that large stall regulated wind turbines may suffer from stall induced vibrations has to some extent hindered the development of large stall controlled HAWTS.

The dynamic behaviour of wind turbine rotor blades in stall has been investigated in order to clarify the importance of stall induced vibrations, identify the physical phenomena involved and to set up design guidelines for the next generation of larger and possibly more flexible stall regulated wind turbines.

The work programme involved coordinated measurement and theoretical modeling of four stall regulated turbines ranging in size from 21 m to 40 m diameter.

The stalling process was examined in terms of quasi-static and unsteady inflow.

The quasi-static modal damping coefficient was identified as an important parameter in determining a rotor's susceptibility to stall induced vibrations. However, the use of quasi-static aerodynamics in wind turbine aeroelastic codes was shown to be deficient when calculating stalled rotor dynamic performance.

The inclusion of unsteady aerodynamic models within the aeroelastic codes was found to considerably improve the agreement between measured and predicted dynamic behaviour of stalled rotors.

A parametric study was performed to determine the sensitivity of the modal damping coefficient to blade parameters. Specifically the effect of scale was investigated. It was found that with the exception of the effects of Reynolds' number the susceptibility of structurally similar rotors to stall induced vibrations should not increase with size.

A procedure for designing a stall regulated rotor was defined which allows the likelihood of a new rotor's susceptibility to stall induced vibrations to be assessed.