Study the effect of using a dual rotor system on the performance of horizontal axis wind turbines using CFD

Abstract

This research aims to improve the power output of a horizontal axis wind turbine (HAWT) by using an auxiliary rotor in front of the main rotor, this configuration is called a dual-rotor wind turbine (DRWT). The three-bladed main rotor has a diameter of 0.9 m and both rotors with NREL S826 airfoil. ANSYS Fluent CFD simulation was used to optimize the DRWT performance where the numerical model was solved using the Realizable k-ɛ turbulence model. Four parameters are used, diameter ratio between the auxiliary front rotor and the main rear rotor (D_R = 0.25, D_R = 0.5, and D_R = 0.75), axial free stream velocity according to the normal wind speed range in Egypt (V_o = 5 m/s, V_o = 7.5 m/s, and V_o = 10 m/s), tip speed ratio which ranges from 2 to 8, and the number of blades of the front rotor (B = 2, B = 3 and B = 4). The results show that increasing the number of blades positively impacts performance but at lower tip speed ratios. Smaller diameter ratios yield better performance, while increasing wind speed results in higher power. The best performance was achieved at freestream velocity V_o = 10 m/s, diameter ratio D_R = 0.25, front rotor number of blades B = 4, and tip speed ratio λ = 5 in which the overall maximum power coefficient Cp max = 0.552 with an increase with 36.75 % compared to the single rotor case.