Tonio Sant

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.

Validating BEM, Direct and Inverse Free Wake Models with the MEXICO Experiment

The primary objective of the MEXICO (Model Experiments in Controlled Conditions) project was to generate experimental data for validation of models for wind turbines. Kulite©pressure sensors were used for pressure measurements while Particle Image Velocimetry was used with the aim of tracking the tip vortex trajectory. The pressure measurements were carried out for both axial and yawed flow conditions with yaw angles of 15o; 30o and 45o. For the Particle Image Velocimetry measurements data was gathered for axial flow and for the ±30o yaw cases at a single tip speed ratio. In this work, an inverse free wake lifting line model, a direct free wake model and a BEM model are validated with the MEXICO data. Particular emphasis is placed on the study of yawed flow conditions. The inverse free-wake model makes use of the experimental loads as input in order to find the distribution of inductions and angle of attack. The predictive capability of BEM may therefore be assessed based on this. Validation of the inverse free-wake model was performed by investigating the stagnation pressureprediction as well as the vortex trajectory prediction. This was done by means of the PIV data gathered from the MEXICO experiment. This PIV data was also used for validation purposes of the direct free-wake model. The differences in the angle of attack distributions in yawed flow with these models was studied in order to assess the difference in results between the use of 2D and 3D airfoil data.

IEA wind annex XX: HAWT aerodynamic and models from wind tunnel measurements - final report

This work characterizes undocumented physical relationships that govern aerodynamic force time variations that take place in connection with rotational augmentation on rotating wind turbine blades.

Estimating the Unsteady Angle of Attack from Blade Pressure Measurements on the NREL Phase VI Rotor in Yaw using a Free-Wake Vortex Model

The unsteady aerodynamic phenomena associated with yawed wind turbines are still poorly understood and are therefore challenging to predict accurately. The main issues concern the geometry of the skewed vortical wake formed behind the turbine, the unsteady flow field at the rotorplane induced by the vortical wake, as well as the aerodynamic effects of unsteady flow over the blade sections. Blade pressure measurements on a rotating blade of a yawed wind turbine can be very useful in obtaining further insight of yaw aerodynamics. However, in doing so, knowledge of the time-dependent angle of attack and induced velocity distributions at the rotoplane is an indispensable requirement. This paper presents a method to derive such distributions for the NREL phase VI turbine using a free-wake vortex model. The study considered different operating conditions in yaw that yielded both attached and separated flows over the blades. The derived free-wake geometry solutions are plotted together with the corresponding wake trailing and shed circulation distributions. These plots help investigate how the unsteady bound circulation formed at the blades is eventually convected into the wake. The derived results are helpful to develop more reliable aerodynamic models for wind turbine design codes.