Surrogate modelling for high-lift multi-element hydrofoil shape optimization of a hydrokinetic turbine blade

The hydrodynamic shapeof a blade is one of the most important factorsin the design process of a horizontal axis hydrokinetic turbinethat influencesits performance. The present work is focused on thedesign and hydrodynamic analysis of a high-lift system using the optimization methodof surrogate models and computational fluid dynamics(CFD)analysis.The parameters that affectthe amount of the lift and the drag force thata hydrofoil cangenerate are the gap, the overlap, the flap deflection angle(δ), the flap chord length(C2) andthe angle of attackof the hydrofoil(α). These factors were varied to examine theturbine performancein terms ofthe ratio between the lift (CL) and the dragcoefficient(CD), and the minimum negative pressure coefficient (min Cpre) in order toavoid the cavitation inception. For this propose, surrogatemodels were implemented to analyse the CFDresultsand find the optimal combination of the design parameters of the high-lift hydrofoil.ThetraditionalEppler 420 hydrofoil was utilized for the design of the multi-element profile, which wascomposed of a main element and a flap. The multi-element design selected as optimal had a gap of 2.825 %C1, an overlap of 8.52 %C1, a δ of 19.765 ̊, a C2of 42.471 %C1and a αof -4 ̊, where C1refers to the chord length of the main element.In comparison with the traditionalEppler 420hydrofoil,CL/CDratio increasesfrom 39.050 to 42.517.