Wouter Haans

Measurement of Tip Vortex Paths in the Wake of a HAWT Under Yawed Flow Conditions

Tip vortex locations have been measured in the wake of a model rotor in both axial flow and yaw using quantitative flow visualization. For each setting, the axial force coefficient has been derived, as well, from measurements. The results agree well with those previously published on the Delft University of Technology model rotor. The main interest is to determine the tip vortex pitch, wake skew angle, wake expansion, and to physically interpret the data. The results also help to validate and construct models. The tip vortex location data complement the existing skewed wake velocity data from hot-wire anemometry, making it a valuable experimental database.

Measurement and Modelling of Tip Vortex Paths in the Wake of a HAWT under Yawed Flow Conditions

Tip vortex locations have been measured in the wake of a model rotor in both axial flow and yaw using quantitative flow visualisation. For each setting, the axial force coefficient has been derived as well from measurements. The results seem to agree well with those previously published on the Delft University of Technology model rotor. The main interest is to determine the tip vortex pitch, wake skew angle and wake expansion and to physically interpret the data. The results should also help to validate and construct models. The tip vortex locations data complement the existing skewed wake velocity data from hot-wire anemometry, making it a valuable experimental database.

Suppression of Classical Flutter using a 'Smart Blade'

Future horizontal axial w ind turbine s that approach the 10MW capacity will have a rotor di ameter somewhere in the order of 170m. The ir loads could be much higher and their blades more flexible compared to current multi -MW wind turbines, most probably resulting in aeroelastic instabilities not commonly seen in the machines of today. The likely d esign drivers for future 10MW+ wind turbines are fatigue life and aeroelastic stability. To help improve the fatigue life and the aeroelastic stability, load control could be applied to future wind turbines. This paper concerns t he load control concept of an actuated trailing edge flap (TEF) , focusing on the effects they have on the aeroelastic stability of a blade . I n particular, the two degree of freedom Flap -Torsion Flutter instability -Classical Flutter - is studied . A modal representation of the turbine dynamics (eigenmodes and eigenfrequencies) , an unsteady BEM model and a simple controller for the actuated trailing edge are coupled to form an aero -servo -elastic model. Its unsteady airfoil model is based on Theodorsen’s theory , modified to include the ef fects of unsteady trailing edge flap deflections . The aero servo -elastic model of the wind turbine is designed with the intention to capture the Classical Flutter instability . It is demonstrated that an extension of the stable operating range beyond the or iginal Flutter limit is feasible when using an actuated trailing edge flap , combined with a simple controller .

Experimentally observed effects of yaw misalignment on the inflow in the rotor plane

Near-wake measurements, focussed on yawed flow conditions, are conducted on a wind turbine rotor model in an open jet wind tunnel. Tip vortex center locations and phase-locked average flow velocity distributions are recorded. Experimental conditions at the blade are not measured and hence are estimated from a measurement analysis tool, named inverse vortex wake model. The unknown bound circulation is derived by the vortex wake type method without the need for an airfoil model. The analysis of the effects yawed operating conditions have on the blade flow conditions concentrates on the individual contributions of tip, root, trailed and shed vortices to the inflow in the rotor plane.

The inverse vortex wake model: a measurement analysis tool

To reduce the level of uncertainty associated with current rotor aerodynamics codes, improved understanding of rotor aerodynamics is required. Wind tunnel measurements on model rotors contribute to advancing our knowledge on rotor aerodynamics. The combined recording of blade loads and rotor wake is desired, because of the coupled blade and wake aerodynamics. In general, however, the small size of model rotors prohibits detailed blade load measurements; only the rotor wake is recorded. To estimate the experimental blade flow conditions, a measurement analysis tool is developed: the inverse vortex wake model. The rotor wake is approximated by a lifting line model, using rotor wake measurements to reconstruct the vortex wake. Conservation of circulation, combined with the Biot-Savart law, allows the induced velocity to be expressed in terms of the bound circulation. The unknown bound circulation can be solved for, since the velocity is known from rotor wake measurements. The inverse vortex wake model is subsequently applied to measurements on the near wake of a model rotor subject to both axial and yawed flow conditions, performed at a TUDelft open jet wind tunnel. The inverse vortex wake model estimates the unsteady experimental blade flow conditions and loads that otherwise would have remained obscured. Copyright