Downstream tidal turbine transient local blade loading characterization

Flow perturbations carried in the wake of an upstream turbine can have a significant impact on the local and transient loads observed on the downstream one. To get a better understanding of the effect of unsteady asymmetric flow on the load felt by a downstream turbine and develop a method to extract local and transient blade loading from CFD results, fully transient simulations designed to study this effect were performed with a RANS k-ω SST turbulence model using ANSYS-CFX. A horizontal axis tidal turbine (HATT) was used for the study. Three configurations were considered: the downstream turbine aligned with the upstream one, the downstream turbine offset by 0.5 D and finally offset by 1 D , with D being the diameter of the turbine. A 10 D clearance between both turbines was used. Results show that when fully in-line, the downstream turbine sees reduction in power coefficient by almost 70 %, with a temporal variation of this coefficient having a relative amplitude of more than 30 %. Furthermore, the blades see localized loading varying by a factor of up to 2 during their rotation and the changes in the load amplitude applied at the same location are varying by more than 13 %. Blade load and flap-wise bending moment display significant amplitude variations for the 0 D and 0.5 D offsets, with values 8 and 12 times higher to what is observed for the 1 D offset. • Transient characterization of a downstream turbine subjected to the wake of an upstream turbine was performed. • Variations in global downstream turbine coefficients of performance and thrust were seen to vary greatly. • Presentation ofmethodology to obtain local blade thrust coefficients that vary by up to 100% locally during bladerotations.