Performance assessment of straight and linearly tapered rotors through wind tunnel investigation for off-grid applications

Abstract

The development of commercial wind turbine (WT) blade often accompanies many challenges due to its complex design process, geometric configuration and associated cost. In this backdrop, the article tries to put forward the applicability of a much simpler form of WT blades, which could be used in place of blade element momentum theory (BEMT) based turbine blades. In the present investigation, four small-scale horizontal-axis wind turbines model rotors having NACA0012 as its sectional profile has been designed and tested. The three model rotors opted to have straight and linearly tapered (SLT) blades, have been chosen in reliance on their simplicity and ease of fabrication. They are differentiated based on the root chord to tip chord ratio as M1 (1:1), M2 (5:3) and M3 (5:2), and subsequently compared with a BEMT rotor of a similar operational configuration. The wind tunnel investigation shows that the power coefficient for M1 is higher than M2 and M3. The favourable models M1 and M2 are capable of capturing power coefficient of, 37% and 24%. respectively, of the Betz-Joukowsky limit while operating at blade pitch angle less than 30°. Based on their operational characteristics, it is suggested to operate the modelled SLT rotors in the potential generation phase of the power characteristics curve to avoid a sudden drop in the rotor rotational speed.