Numerical Analysis on the Effectiveness of Gurney Flaps as Power Augmentation Devices for Airfoils Subject to a Continuous Variation of the Angle of Attack by Use of Full and Surrogate Models

Francesco Balduzzi,Zbigniew Buliński,Piotr Wiśniewski,Alessandro Bianchini

doi:10.3390/en13081877

Francesco Balduzzi, Zbigniew Buliński + Show 2 more

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https://doi.org/10.3390/en13081877

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Abstract

The disclosing of new diffusion frontiers for wind energy, like deep-water offshore applications or installations in urban environments, is putting new focus on Darrieus vertical-axis wind turbines (VAWTs). To partially fill the efficiency gap of these turbines, aerodynamic developments are still needed. This work in particular focuses on the development of a mathematical model that allows predicting the possible performance improvements enabled in a VAWT by application of the Gurney flaps (GFs) as a function of the blade thickness, the rotor solidity and geometry of the Gurney flap itself. The performance of airfoil with GFs was evaluated by means of detailed simulations making use of computational fluid dynamics (CFD). The accuracy of the CFD model was assessed against the results of a dedicated experimental study. In the simulations, a dedicated method to simulate cycles of variation of the angle of attack similar to those taking place in a cycloidal motion (rather than purely sinusoidal ones) was also developed. Based on the results from CFD, a multidimensional interpolation based on the radial basis functions was conducted in order to find the GF design solution that provides the highest efficiency for a given turbine in terms of airfoil and solidity. The results showed that, for the selected study cases based on symmetric airfoils, the GF positioned facing outwards from the turbine, which provides the upwind part of the revolution, can lead to power increments ranging from approximately 30% for the lower-solidity turbine up to 90% for the higher-solidity turbine. It was also shown that the introduction of a GF should be coupled with a re-optimization of the airfoil thickness to maximize the performance.

Highlights

For the sake of brevity, only the results with a one-sided Gurney flaps (GFs) (2.5%c) are reported here: Figure displays the comparison of static polars and Figure the performance in sinusoidal movement within an AoA range between 10 and 30 deg and a reduced frequency k of 0.05
The fish tail shape is more suitable for turbines with lower solidity, while the one-sided Gurney flap configuration significantly influences the performance of turbines with higher solidity values
The tendencies are thought to be of general application and they clearly highlight the potential of GFs for use in Darrieus vertical-axis wind turbines (VAWTs)

Summary

Introduction

One of the leading technologies is wind energy, which is reaching a cost of energy competitive (in the case of large rotors) with other conventional sources. The majority of installed wind energy power today comes from wind farms made of several large horizontal axis wind turbines (HAWTs), the disclosing of new diffusion frontiers like deep-water offshore applications or installations in densely inhabited environments. 22 of of 25 frontiers like deep-water offshore applications or installations in densely inhabited environments are are putting focus different turbinearchitectures, architectures,like likeDarrieus. Darrieusvertical vertical axis axis wind wind turbines putting newnew focus on on different turbine turbines (VAWTs) [1]. This technology has some undisputed advantages (e.g., the insensitivity to wind (VAWTs) [1]. This technology has some undisputed advantages (e.g., the insensitivity direction, to wind the possibility of puttingofthe generation system on the ground, the lower to highly direction, the possibility putting the generation system on the ground, thesusceptibility lower susceptibility to turbulent flows [2,3]), but their efficiency is lower compared to that of HAWTs

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