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

Abstract

The hydrodynamic shape of a blade is one of the most important factors in the design process of a horizontal axis hydrokinetic turbine that influences its performance. The present work is focused on the design and hydrodynamic analysis of a high-lift system using the optimization method of surrogate models and computational fluid dynamics (CFD) analysis. The parameters that affect the amount of the lift and the drag force that a hydrofoil can generate are the gap, the overlap, the flap deflection angle (δ), the flap chord length (C2) and the angle of attack of the hydrofoil (α). These factors were varied to examine the turbine performance in terms of the ratio between the lift (CL) and the drag coefficient (CD), and the minimum negative pressure coefficient (min Cpre) in order to avoid the cavitation inception. For this propose, surrogate models were implemented to analyse the CFD results and find the optimal combination of the design parameters of the high-lift hydrofoil. The traditional Eppler 420 hydrofoil was utilized for the design of the multi-element profile, which was composed 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 C2 of 42.471 %C1 and a α of-4˚, where C1 refers to the chord length of the main element. In comparison with the traditional Eppler 420 hydrofoil, CL/CD ratio increases from 39.050 to 42.517.