Titel: Vortex System Studies on Small Wind Turbines, FOI-R-0936-SE
Författare/Author: Björn Montgomerie & Jan-Åke Dahlberg
Utgivare/Publisher: Totalförsvarets forskningsinstitut (FOI), Vindforsk
Årtal/Year: 2003
Ämnesord/Subject: Mekanik och aerodynamik
Sökord/Keywords: Wind turbine, aerodynamics, induction, performance, tip vortex, tip vortices, Reynolds number
Rapport (Pdf)
Sammanfattning/Abstract: The wind tunnel experiment reported included a small wind turbine setup and smoke to visualize the trailing tip vortices for different wind turbine configurations. Several combinations of tunnel wind speeds and tip speed ratios generated a database where the end result were radius and pitch, of the tip vortex spirals, as functions of the downstream coordinate. he Reynolds number in the experiment was very low compared to that of full size turbines. The results should therefore be seen as valid only for low Reynolds numbers. The models were 18 and 25 cm diameter turbines. This is thought to be complementary to the information obtained in similar wind tunnel investigations for much larger models.
The database is meant to be a fundamental tool for the construction of practical aerodynamic induction methods. Such methods typically employ the Biot-Savart law. However, the pure application of the Biot-Savart law has been shown to lead to a flow field, which deviates considerably from that of reality. E.g. the concentration into tip vortices does not happen when the flow is simulated with Biot-Savart law only. Thus, for
practical application the induction method must be modified, based on investigations such as the one reported. It is foreseen replace the widely used Blade Element Momentum method for wind turbine loads and performance prediction.