Influence of the number of front and rear rotor blades on the hydrodynamic performance of counter-rotating horizontal-axis tidal turbines

The coaxial rotor structure presents significant potential for the development of tidal turbines. In order to study the effect of the number of front and rear rotor blades on the hydrodynamic performance of counter-rotating horizontal-axis tidal turbines (CRHATTs), three models (CRHATT 3-2, CRHATT 3-3 and CRHATT 3-4) are established at the same tip speed ratio (TSR), and the accuracy of the numerical method is verified by experiments. The effect of blade number on the performance coefficients, velocity and pressure pulsations and vortex structure of CRHATTs are calculated based on CFD method and spectral analysis. The results show that the relationship of the power coefficient for the three models is: CRHATT 3-4 > CRHATT 3-3 > CRHATT 3-2. The turbulent kinetic energy in the flow field can be transferred more quickly from the large-scale vortex structure to the small-scale as the number of rear rotor blades increases. By weighing aspects such as load fluctuation and power coefficient, the CRHATT 3-4 can produce the largest power coefficients, the best stability during operation and the least vibration on the blades among the three models. This paper provides significant guidance for the engineering design and optimization research of CRHATTs.