Effects of Reynolds number and different tip loss models on the accuracy of BEM applied to tidal turbines as compared to experiments

The Blade Element Momentum (BEM) model is an important tool in initial turbine design and analysis, and its accuracy is dependent on various factors. Two factors were studied in this paper, and the results were compared across 2 scaled tidal turbines. Firstly, the effect of using multiple sets of lift and drag coefficients of the airfoil for different Reynolds numbers versus that of using a single set of lift and drag coefficients was studied. The predicted power coefficient increased at higher rotational speed when using multiple sets of airfoil data, while there was no conclusive effect on the thrust coefficients. Secondly, the performance of BEM with various tip loss models (Prandtl, Goldstein׳s momentum averaging factor, and Shen׳s corrections) was compared against experimental data of one of the scaled tidal turbine. Prandtl׳s tip loss correction predicted higher power and thrust coefficients compared to Goldstein׳s momentum averaging factor. Shen׳s correction increased the power coefficient at higher rotational speed, but decreased the thrust coefficient for the whole range of rotational speed being considered.