Design improvement of flapping hydrokinetic turbines
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ORIGINAL PAPER
Design improvement of flapping hydrokinetic turbines Benarfaoui Arfaoui1 · Bouzaher Mohamed Taher2 · Belhi Guerira1 Received: 20 August 2019 / Accepted: 29 May 2020 © Sociedade Brasileira de Engenharia Naval 2020
Abstract This investigation deals with the flow control and the enhancement of the output power of a flapping foil turbine. The connected gurney flap (GF) is a small arc that oscillates with a given pitching angle. The incompressible laminar flow around a simple flat plate equipped with an oscillating gurney flap is solved using a computational method. A user-defined function and a coupled layering/sliding dynamic mesh technique available in ANSYS FLUENT.15 are used to adjust both the blade and the flap positions during the turbine flapping cycle. It was shown that an appropriate synchronization between the flap oscillation and the turbine blade rotation could modify the blade flap camber, which corrects, in turn, the pressure distribution and therefore boosts the lift force during both the up-stroke and down-stroke stages. The application of this strategy of control enhances the output power dramatically compared with a clean flapping turbine blade. Keywords Gurney flap · Flapping turbine · Flow control · Leading edge vortex
1 Introduction Renewable energies are able to provide free power with negligible or at least acceptable constructive effects. The common devices used to extract marine energy are turbines with rotating blades. Flapping foil turbine is considered as a promising energy extractor that is able to provide free power from any free surface waves or uniform streams. The effectiveness of these devices represents the main objective of several researches [1–5]. Researches carried out point that flapping turbine can operate at low Reynolds number and, furthermore, with low flapping frequencies, which supports the use of this type of turbines. It is well proved that passive and active flow control techniques are able to improve the efficiency of flapping foil turbine [6–10]. The control techniques used in flapping foil turbine can be classified in two groups. The first one is the control of the motion parameters, which may have a strong effect on the turbine performance. Recall that the conventional flapping foil has a harmonically heaving motion and a pitching motion around an axis fixed between the blade and the * Bouzaher Mohamed Taher [email protected] 1
Département de Génie Mécanique, Université de Biskra, 07000 Biskra, Algeria
Scientific and Technical Research Centre for Arid Areas (CRSTRA), Biskra, Algeria
2
power storage device. The second type of control technique is based on modifying the blade shape, which ensures an attached flow along the blades surface. Ashraf et al. [2] investigated the effect of a modified non-sinusoidal foil motion on the turbine performance. It was found that the extracted power increased by 17%. Xiao et al. [11] proved that using trapezoidal-like pitching motion instead of sinusoidal motion increased efficiently the output
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