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

Abstract

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