Damping the fluctuating behaviour and improving the convergence rate of the axial induction factor in the BEMT-based rotor aerodynamic codes

This source preferred by Siamak Noroozi and John Vinney

Authors: Maheri, A., Noroozi, S., Toomer, C.A. and Vinney, J.

http://www.ewec2006proceedings.info/allfiles2/0545_Ewec2006fullpaper.pdf

Start date: 27 February 2006

Publisher: EWEA

Place of Publication: Brussels

Rotor aerodynamic codes which are based on the Blade Element Momentum Theory are iterative in nature. They experience the common problem of fluctuating behaviour of the axial induction factor in its iteration loop. A simple method has been introduced in order to both prevent this fluctuating behaviour and improve the convergence rate.

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Authors: Maheri, A., Noroozi, S., Toomer, C. and Vinney, J.

Journal: European Wind Energy Conference and Exhibition 2006, EWEC 2006

Volume: 2

Pages: 1176-1179

ISBN: 9781622764679

A common problem in the rotor aerodynamic codes which are based on the Blade Element Momentum Theory is the fluctuating behaviour of the axial induction factor in its iteration loop. These fluctuations are due to periodically switching of the loading state between light and heavy. Normally in such situations, after a predefined maximum number of iterations, the iteration process stops and the program skips that blade segment. This impacts both the accuracy of the predicted results and the code performance. This paper presents a method to avoid this behaviour by using a relaxation factor applicable in the iteration process. By this, no matter how high the amplitudes of the fluctuations, using a proper relaxation factor leads to a converged solution. This method also uses the first few iterated values to predict the neighbourhood of the final converged axial induction factor. This can be used to accelerate the convergence process. It has been shown that selection of a proper relaxation factor together with a simple modification to the predicted axial induction factor after a few iterations highly improves the convergence rate. © 2006 APC Power Conversion Ltd.

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