Abstract
Abstract. Current fast aeroelastic wind turbine codes suitable for certification lack an induction model for standstill conditions. A trailed vorticity model previously used as an addition to a blade element momentum theory based aerodynamic model in normal operation has been extended to allow computing the induced velocities in standstill. The model is validated against analytical results for an elliptical wing in constant inflow and against standstill measurements from the NREL/NASA Phase VI unsteady experiment. The extended model obtains good results in the case of the elliptical wing but underpredicts the steady loading for the Phase VI blade in attached flow. The prediction of the dynamic force coefficient loops from the Phase VI experiment is improved by the trailed vorticity modeling in both attached flow and stall in most cases. The exception is the tangential force coefficient in stall, where the codes and measurements deviate and no clear improvement is visible. This article also contains aeroelastic simulations of the DTU 10 MW reference turbine in standstill at turbulent inflow with a fixed and idling rotor. The influence of the trailed vorticity modeling on the extreme flapwise blade root bending moment is found to be small.
Highlights
A trailed vorticity model previously used as an addition to a blade element momentum theory based aerodynamic model in normal operation has been extended to allow computing the induced velocities in standstill
The model is validated against analytical results for an elliptical wing in constant inflow and against standstill measurements from the NREL/NASA Phase VI unsteady experiment
State-of-the-art aeroelastic wind turbine codes that are suitable for simulating the many time series needed for certification typically use an aerodynamics model based on blade element momentum (BEM) theory
Summary
State-of-the-art aeroelastic wind turbine codes that are suitable for simulating the many time series needed for certification typically use an aerodynamics model based on blade element momentum (BEM) theory. Because the near-wake model is mainly meant to capture trailed vorticity effects close to the blade, the local inflow angle is used as helix angle φ This inflow angle is computed based on the velocity triangle at the vortex trailing point and is affected by the free wind speed including turbulence, the movement of the blade and the induced velocities due to near and far wake. This way the near-wake flow situation depends only on the velocities at the blade section, which is similar to how the 2-D unsteady aerodynamics effects are computed; see Hansen et al (2004). The only deviation from the basic structure of the implementation from the structure outlined in Fig. 3 of the article by Pirrung et al (2017) is that no far-wake model is used because the BEM modeling is not valid in standstill conditions and the near-wake model computes the full induction due to the semi-infinite trailed vorticity behind the blades
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