Aerodynamic Characterization of a Wells Turbine under Bi-directional Airflow

Puddu, Pierpaolo; Paderi, Maurizio; Manca, C

doi:10.1016/j.egypro.2014.01.030

Cited by 33 publications

(24 citation statements)

References 17 publications

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“…Wells turbines have been studied extensively, both experimentally [15,31,24,63,74,53,57,48] and numerically [40,62,17,76,30,72,32,27], but mainly from a first-law perspective. More recently, a number of authors [66,67,68,69,71] have focused on the irreversibilities in this component, trying to link the amount of available work (exergy) and the entropy produced.…”

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confidence: 99%

Numerical evaluation of entropy generation in isolated airfoils and Wells turbines

et al. 2018

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In recent years, a number of authors have studied entropy generation in Wells turbines. This is potentially a very interesting topic, as it can provide important insights into the irreversibilities of the system, as well as a methodology for identifying, and possibly minimizing, the main sources of loss. Unfortunately, the approach used in these studies contains some crude simplifications that lead to a severe underestimation of entropy generation and, more importantly, to misleading conclusions. This paper contains a re-examination of the mechanisms for entropy generation in fluid flow, with a particular emphasis on RANS equations. An appropriate methodology for estimating entropy generation in isolated airfoils and Wells turbines is presented. Results are verified for different flow conditions, and a comparison with theoretical values is presented. 1Wells turbines have been studied extensively, both experimentally [15,31,24,63,74,53,57,48] and numerically [40,62,17,76,30,72,32,27], but mainly from a first-law perspective. More recently, a number of authors [66,67,68,69,71] have focused on the irreversibilities in this component, trying to link the amount of available work (exergy) and the entropy produced.The application of second-law analyses is not novel, as such analyses have been done by many authors, but mainly from a system perspective: Bejan [8,9] presents an extensive review of the application to different thermodynamic systems. Similar approaches have been used in the analysis of thermal power plants [39], wind turbines [56,6,7,60,52], and vortex generators [33].Computational Fluid Dynamics (CFD), aside from making possible a more rapid and economic evaluation of many systems (compared to experimental testing), can provide a better and more detailed understanding of many phenomena, by capturing a level of detail that would be extremely difficult in an experimental study. It allows a very fine decomposition of the overall problem that can be used to locate the sources of irreversibility within the system. Entropy generation by thermal and viscous sources can be calculated directly by post-processing the fields of thermo-and fluid-dynamic variables available from the numerical solution [8]. However, particular attention needs to be paid to the nature of the flow and to the solution approach. While in laminar flows all entropy generation is directly found in the CFD solution [18,2,70,33,79,59], this is not true for turbulent flows, unless a Direct Numerical Simulation (or DNS) is used. However, with current computational resources, the use of DNS is still impractical even for moderately large Reynolds numbers. To make high-Reynolds-number flows treatable, the governing equations are either averaged (leading to the Reynolds Averaged Navier Stokes equations, or RANS) or filtered (leading to the Large Eddy Simulation approach, or LES).Moore and Moore [49, 50] present a methodology for calculating entropy production in viscous flows, using RANS equations. They divide the mean entropy production into the contr...

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Numerical evaluation of entropy generation in isolated airfoils and Wells turbines

et al. 2018

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“…As a Wells turbine operates with a low subsonic flow (in the incompressible range), aerodynamic performance curves, when represented in non-dimensional terms, are a function of only the Reynolds number. Moreover, this being a weak dependency within the range spanned in the experiments [35,43], the expected variation in performance due to changes in rotational speed is minor [44], certainly lower than the uncertainty due to A more detailed validation and analysis of the flow field in this turbine has been presented in [24,39], while different geometries and operating conditions were studied in [36,45]. The interested reader is referred to these works for in-depth analyses of the impact of turbulence closure and dynamic operating conditions on Wells turbine performance.…”

Section: Free Form Deformationmentioning

confidence: 89%

“…Simulations that did not converge after 3000 iterations were stopped, and the blade was considered stalled. With these settings, the variation in torque coefficient with flow coefficient was plotted in Figure 5, which also shows experimental data for an identical turbine at two rotational speeds [35], the one used in this work and a smaller one, which leads to a larger operating range. As a Wells turbine operates with a low subsonic flow (in the incompressible range), aerodynamic performance curves, when represented in non-dimensional terms, are a function of only the Reynolds number.…”

Section: Free Form Deformationmentioning

confidence: 99%

Optimization of blade profiles for the Wells turbine

et al. 2018

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A Wells turbine, when coupled with an oscillating water column, allows the generation of power from the energy in waves on the surface of the ocean. In the present work, a tabu search is used to control the process of optimising the blade profile in the Wells turbine for greater performance, by maximising the torque coefficient. A free form deformation method is used as an efficient means of manipulating the blade profile and computational fluid dynamics in OpenFOAM are used to assess each profile in both two and three dimensions. Investigations into both the flow coefficient at which the optimisation is performed and the number of control variables in the free form deformation tool are performed before optimisations are done on a two-dimensional blade at the hub and tip solidities. This results in increases to the torque coefficient of 34% and 32% at the tip and hub solidities, respectively. These results are then applied to the three-dimensional turbine, giving a 14% increase in the torque coefficient. The results are assessed and an improved method of optimising the blade in two dimensions is proposed.

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“…This work can simulate the real operation of a wave energy conversion device based on the principle of an (OWC) equipped with a W-T [107,210]. This work can simulate the real operation of a wave energy conversion device based on the principle of an (OWC) equipped with a W-T [107,210].…”

Section: Validation Of Cfd Modelsmentioning

confidence: 99%

“…The most recent experimental setup was performed by the Department of Mechanical, Chemical and Materials Engineering of the University of Cagliari. This work can simulate the real operation of a wave energy conversion device based on the principle of an (OWC) equipped with a W-T [107,210]. Wave motion is reproduced by means of a piston moving inside a chamber generating the periodic bidirectional airflow through the turbine.…”

Section: Validation Of Cfd Modelsmentioning

confidence: 99%

Wells turbine for wave energy conversion: a review

Shehata

Xiao

Saqr

et al. 2016

Int. J. Energy Res.

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Summary In the past 20 years, the use of wave energy systems has significantly increased, generally depending on the oscillating water column concept. Wells turbine is one of the most efficient oscillating water column technologies. This article provides an updated and a comprehensive account of the state‐of‐the‐art research on Wells turbine. Hence, it draws a roadmap for the contemporary challenges, which may hinder future reliance on such systems in the renewable energy sector. In particular, the article is concerned with the research directions and methodologies, which aim at enhancing the performance and efficiency of Wells turbine. The article also provides a thorough discussion of the use of CFD for performance modeling and design optimization of Wells turbine. It is found that a numerical model using the CFD code can be employed successfully to calculate the performance characteristics of W‐T as well as other experimental and analytical methods. The increase of research papers about CFD, especially in the last 5 years, indicates that there is a trend that considerably depends on the CFD method. Copyright © 2016 John Wiley & Sons, Ltd.

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Aerodynamic Characterization of a Wells Turbine under Bi-directional Airflow

Cited by 33 publications

References 17 publications

Numerical evaluation of entropy generation in isolated airfoils and Wells turbines

Numerical evaluation of entropy generation in isolated airfoils and Wells turbines

Optimization of blade profiles for the Wells turbine

Wells turbine for wave energy conversion: a review

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