Analysis of a lift augmented hydrofoil for hydrokinetic turbines

Abstract

In the last years, increased attention has been given to hydrokinetic energy technologies due to these turbines represent an attractive technology for the harnessing of a huge untapped renewable energy potential in oceans, seas but also in rivers and canals. However, the low efficiency is an important barrier to its commercialization. The aim of this study is to present the selection of a multi-element hydrofoil that can enhance the hydrokinetic turbine performance. Therefore, in order to examine the influence of the type of airfoil used, as multi-element hydrofoil, on the blade performance, several studies using JavaFoil software were performed. The result indicates that hydrofoil multi-element Eppler 420 can provide high efficiency of the turbine because it has a higher relationship between the lift and drag coefficients C Lmax /C D (47.77) compared to the Selig S1223 profile (39.59) and other hydrofoils studied. Furthermore, computational fluid dynamics (CFD) was used to obtain the hydrodynamic characteristics of the hydrofoil Eppler 420 with and without flap. The CFD simulations were carried out using ANSYs-Fluent software. It was observed that there is an increase in the lift coefficient by 69.46% and 471.39 % for the hydrofoil with flap and a chord length of 30%, and a chord length of 70%, respectively, under the analyzed conditions with respect to the hydrofoil without flap.

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

“…In general, the objective of the hydrodynamic shape optimization, for a given operating condition, is to design a hydrofoil that maximizes CL, or minimizes CD, or maximizes the lift-to-drag ratio (CL/CD); which is subjected to several constraints, such as the minimum negative pressure coefficient (min Cpre) for avoiding the cavitation inception, as well as geometrical constraints, among others [1,[3][4][5][13][14].…”

“…Overlap (ovl) is the flap leading-edge position on the xaxis and gap is the flap leading-edge position on the yaxis. In turn, C, which is equal to 0.1773 m in this study, C1 and C2, are the chord length of the blade, the length of the main element and length of flap, respectively [3][4][5]. It is noteworthy that changing the values of the gap and the overlap slightly resulted in a significantly different hydrodynamic performance for the multi-element hydrofoil.…”

“…A main objective of hydrokinetic turbine designers is to maximize the performance and reduce manufacture costs [1][2]. One possible way to reach the objective of maximizing the power coefficient (Cp) is to design highlift systems consisting of a hydrofoil with a flap [3][4]. This geometrical configuration results in the maximization of the lift and the minimization of the flow separation around the hydrofoil [4].…”

“…This geometrical configuration results in the maximization of the lift and the minimization of the flow separation around the hydrofoil [4]. Commonly, flow separation leads to a loss of the lift, an increase of the drag and, therefore, a reduction of the blade performance [3][4][5].…”

Design and Optimization of a Multi-Element Hydrofoil for a Horizontal-Axis Hydrokinetic Turbine

“…It is important to note that cavitation inception can be predicted from the pressure distribution, since cavitation occurs when the local pressure (P L ) is equal to P V or when the minimum negative pressure coefficient (|minC pre |) is equal to σ [44]. By reviewing atmospheric pressures and temperatures of the regions of interest [45], in addition to previous works [46], a σ value equal to 4 was established. The value of σ was included within the surrogate model as a nonlinear restriction.…”