Design and performance analysis of impulse turbine for a wave energy power plant

Wave energy is the most abundant source of renewable energy in the World. For the last two decades, engineers have been investigating and defining different methods for power extraction from wave motion. Two different turbines, namely Wells turbine and impulse turbine with guide vanes, are most commonly used around the world for wave energy power generation. The ultimate goal is to optimize the performance of the turbine under actual sea conditions. The total research effort has several strands; there is the manufacture and experimental testing of new turbines using the Wave Energy Research Team's (WERT) 0.6 m turbine test rig, the theoretical and computational analysis of the present impulse turbine using a commercial software package and finally the prediction of the performance of the turbine in a representative wave power device under real sea conditions using numerical simulation. Also, the WERT 0.6 m turbine test rig was upgraded with a data acquisition and control system to test the turbine in the laboratory under real sea conditions using the computer control system. As a result, it is proven experimentally and numerically that the turbine efficiency has been raised by 7% by reducing the hub‐to‐tip ratio from 0.7 to 0.6. Effect of tip clearance on performance of the turbine has been studied numerically and designed tip clearance ratio of 1% has been validated. From the numerical simulation studies, it is computed that the mean conversion efficiency is reduced around 5% and 4.58% due to compressible flow and damping effects inside OWC device. Copyright © 2005 John Wiley & Sons, Ltd.     

Computed effect of guide vane shape on performance of impulse turbine for wave energy conversion

This paper deals with the computational fluid dynamics (CFD) analysis on effect of guide vane shape on performance of impulse turbine for wave energy conversion. Initially, experiments have been conducted on the impulse turbine to validate the present CFD method and to analyse the aerodynamics in rotor and guide vanes, which demonstrates the necessity to improve the guide vanes shape. The results showed that the downstream guide vanes make considerable total pressure drop leads low performance of the turbine and hence three‐dimensional (3‐D) inlet and downstream guide vanes have been designed based on well‐known vortex theory to improve the efficiency of the turbine. In order to prove the improvement in efficiency due to 3‐D guide vanes, CFD analysis has been made on impulse turbine with 2‐D and 3‐D guide vanes for various flow coefficients. As a result, it is seen that the present CFD model can predict the experimental values with reasonable accuracy. Also, it is showed from the numerical results that the efficiency of the turbine can be improved by average of 4.5 percentage points by incorporating 3‐D guide vanes instead of 2‐D guide vanes. The physical reason for improvement in efficiency of the turbine due to 3‐D guide vanes has been explained with the CFD flow insight pictures. As the turbine operates in fluctuating flow conditions, the performance of the turbine with 2‐D and 3‐D guide vanes have been calculated numerically using quasi‐steady analysis. Furthermore, the performance of the turbine has been predicted for one year based on Irish wave climate to show the feasibility of using 3‐D guide vanes in actual sea wave conditions. Copyright © 2005 John Wiley & Sons, Ltd.     

A twin unidirectional impulse turbine for wave energy conversion

A twin unidirectional impulse turbine has been proposed in order to enhance the performance of wave energy plant.This turbine system uses two unidirectional impulse turbines and their flow direction is different from each other.However,the turbine characteristics have not been clarified to date.The performances of a unidirectional impulse turbine under steady flow conditions were investigated experimentally by using a wind tunnel with large piston/cylinder in this study.Then,efficiency of the twin impulse turbine have been estimated by a quasi-steady analysis using experimental results.     

Effects of turbine damping on performance of an impulse turbine for wave energy conversion under different sea conditions using numerical simulation techniques

This paper presents the work carried out to predict the behavior of a 0.6 m impulse turbine with fixed guide vanes with 0.6 hub to tip (H/T) ratio under real sea conditions.This enhances the earlier work done by authors on the subject by including the effects of damping applied by the turbine. Real wave data for different wave sites were used as the input data. A typical oscillating water column (OWC) geometry has been used for this simulation. Standard numerical techniques were employed to solve the non-linear behavior of the sea waves. Considering the quasi-steady assumption, uni-directional steady flow experimental data were used to simulate the turbine characteristics under irregular unsteady flow conditions. The test rotor used for this simulation consisted of 30 blades with elliptical profile with a set of symmetric, fixed guide vanes on both up-stream and down-stream sections of the rotor, with 26 vanes each. The results show that the performance of this type of turbine depends on the level of damping applied by the turbine and the prevailing wave site conditions. The objective of this paper is to predict the effects of applied damping on the behavior of impulse turbine under irregular, unsteady conditions for wave power conversion using numerical simulation.     

Impulse turbine with 3D guide vanes for wave energy conversion

In this study, in order to achieve further improvement of the performance of an impulse turbine with fixed guide vanes for wave energy conversion, the effect of guide vane shape on the performance was investigated by experiment. The investigation was performed by model testing under steady flow condition. As a result, it was found that the efficiency of the turbine with 3D guide vanes are slightly superior to that of the turbine with 2D guide vanes because of the increase of torque by means of 3D guide vane, though pressure drop across the turbine for the 3D case is slightly higher than that for the 2D case.     

Enhancing the energy efficiency of the impulse turbine of a wave energy plant

The power take-off mechanism of the oscillating water column based Indian wave energy plant is based on an impulse turbine-permanent magnet synchronous generator (PMSG) set. The MATLAB based simulation of the dynamic model of this power module, considering the plant's operation on the stand-alone mode, is developed incorporating a machine variable model for the PMSG used. It is shown that the energy efficiency of the impulse turbine can be substantially increased by adjusting the load resistance dynamically, as a function of the input differential pressure.     

Computational Fluid Dynamics Benchmark of an Impulse Turbine with Fixed Guide Vanes

This paper presents the comparison of a three dimensional Computational Fluid Dynamics (CFD) analysis with empirical performance data of a 0.6 m impulse turbine with fixed guide vanes used for wave energy power conversion. Pro-Engineer, Gambit and Fluent 6 were used to create a 3-D model of the turbine. A hybrid meshing scheme was used with hexahedral cells in the near blade region and tetrahedral and pyramid cells in the rest of the domain. The turbine has a hub-to-tip ratio of 0.6 and results were obtained over a wide range of flow coefficients. The model yielded a maximum efficiency of approximately 54% as compared to a maximum efficiency of around 49% from experiment. A degree of insight into flow behaviour, not possible with experiment, was obtained.     

2D CFD Analysis and Experimental Analysis on the Effect of Hub to Tip Ratios on the Performance of 0.6 m Impulse Turbine

The objective of this paper is to present the performance comparison of 2D Computational Fluid Dynamics (CFD) analysis with experimental analysis of 0.6 m impulse turbine with fixed guide vanes for both 0.6 and 0.7 hub to tip ratio (H/T). Also the comparison of 2D CFD analysis of the said turbine with different values of H/T ranging from 0.5 to 0.7. A 2D-cascade model was used for CFD analysis while uni-directional steady flow was used for experimental analysis. The blade and guide vane geometries are based on 0.6 m rotor diameter, with optimum profile, and different H/T of 0.5, 0.6 and 0.7. It was concluded from 2D CFD analysis that 0.5 H/T ratio performances was higher than that of 0.6 and 0.7 H/T at peak efficiency and the operational flow range for 0.5 H/T was found to be wider than that of 0.6 and 0.7 H/T ratio.     

Computed effects of tip clearance on performance of impulse turbine for wave energy conversion

This paper depicts numerical analysis on Impulse turbine with fixed guide vanes for wave energy conversion. From the previous investigations, it is found that one of the reasons for the mismatch between computed and experimental data is due to neglecting tip clearance ef fect. Hence, a 3-D model with tip clearance has been generated to predict the internal flow and performance of the turbine. As a result, it is found that the comparison between computed and experimental data is good, quantitatively and qualitatively. Computation has been carried out for various tip clearances to understand the physics of tip leakage flow and effect of tip clearance on performance of such unconventional turbine. It is predicted that the turbine with 0.25% tip clearance performs almost similar to the case of without tip clearance for the entire flow coefficients. The designed value of 1% tip clearance has been validated numerically and computed that the efficiency of the turbine has been reduced around 4%, due to tip clearance flow at higher flow coefficients.     

Performance of Wells Turbine with Guide Vanes for Wave Energy Conversion

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Comparative study of turbines for wave energy conversion

IlltnductionSeveral of the wave energy devices cuntiy stUdiedin the United kingdom, Japan, POhogal, India and othercountries make use of the principle of the oscillatingwater-air coltUnn for convening wave energy to lowPneqmatic energy Which in tUrn can be converted intomechAncal energy. In this case, the developmellt of a bidirechonal air theme has come lip as an importantProblem. So far, a number of self-rechfying air onnesWith different configurations have been ProPOsed, and a; Wells…     

Multiple surrogate based optimization of a bidirectional impulse turbine for wave energy conversion

Oscillating water column based wave energy extracting system has a low efficiency due to the poor performance of its principal power extracting component, the bidirectional turbine. In the present work, flow over a bidirectional impulse turbine was simulated using CFD technique and optimized using multiple surrogates approach. The surrogates being problem dependent may produce unreliable results, if a wrong surrogate is selected. Hence, multiple surrogates such as response surface approximation, radial basis function, Kriging and weighted average surrogates were incorporated in this problem. Same design points were used to generate multiple optima via multiple surrogates to enhance the robustness of the optimization process. Numbers of guide vanes and rotor blades were chosen as the design variables, and the objective was to maximize the blade efficiency. Reynolds-averaged Navier–Stokes equations were solved for analyzing the flow physics. The computed results were used to train the surrogates and find the optimal points via hybrid genetic algorithm. The surrogates were further applied to find the optimal flow parameters by changing flow velocity and turbine speed. The relative efficiency enhancement through our present approach was about 16%. Detailed methodologies, analysis of the results and surrogate applicability have been presented in this paper.     

Effects of blade geometry on performance of wells turbine for wave power conversion

IntroductionThe fossil fuel energy with the problem of airpollution might run out by the middle of the 21stcentury. So many researchers have studied forscores of years on alternative, renewable energysources11] such as tidal, wave, salinity gradient,current, wind and solar energy.The energy density level of waves is higherthan the other energy sources stated above. Thereare various techniques for extraction of energyfrom waves[2]. Several of the wave energydevices using the principle of an os…     

Wells turbine for wave energy conversion: a review

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.     

Wells turbine blade profile optimization for better wave energy capture

Despite the fact that wave energy is available at no cost, it is always desired to harvest the maximum possible amount of this energy. The axial flow air turbines are commonly used with oscillating water column devices as a power take‐off system. The present work introduces a blade profile optimization technique that improves the air turbine performance while considering the complex 3D flow phenomena. This technique produces non‐standard blade profiles from the coordinates of the standard ones. It implements a multi‐objective optimization algorithm in order to define the optimum blade profile. The proposed optimization technique was successfully applied to a biplane Wells turbine in the present work. It produced an optimum blade profile that improves the turbine torque by up to 9.3%, reduces the turbine damping coefficient by 10%, and increases the turbine operating range by 5%. The optimized profile increases the annual average turbine power by up to 3.6% under typical sea conditions. Moreover, new blade profiles were produced from the wind turbine airfoil data and investigated for use with the biplane Wells turbine. The present work showed that two of these profiles could be used with low wave energy seas. Copyright © 2017 John Wiley & Sons, Ltd.     

风力机叶片翼型气动性能数值模拟

采用数值模拟方法对NACA23012,NACA4412,S809,S810等4种常用风力机叶片翼型进行了研究,分析了翼型静止与振荡时的气动性能.随着攻角的增加,静止翼型的升力系数先增大后减小,其阻力系数一直增大,显示出NACA4412翼型具有较好的低风速启动性能;振荡翼型的升力系数随着攻角的变化呈现一个闭合迟滞环曲线,显示出振荡翼型S809的动态失速迟滞效应最为明显.文章参照模拟结果和对比试验数据,验证了数值模拟的可靠性.     

A comparison of two meshing schemes for CFD analysis of the impulse turbine for wave energy applications

This paper presents the comparison of a three-dimensional Computational Fluid Dynamics (CFD) analysis with empirical performance data of a 0.6 m Impulse Turbine with Fixed Guide Vanes used for wave energy power conversion. Pro-Engineer, Gambit and Fluent 6 were used to create a 3-D model of the turbine. A hybrid meshing scheme was used with hexahedral cells in the near blade region and tetrahedral and pyramid cells in the rest of the domain. The turbine has a hub-to-tip ratio of 0.6 and results were obtained over a wide range of flow coefficients. Satisfactory agreement was obtained with experimental results. The model yielded a maximum efficiency of approximately 54% as compared to a maximum efficiency of around 49% from experiment. A degree of insight into flow behaviour, not possible with experiment, was obtained. Sizeable areas of separation on the pressure side of the rotor blade were identified toward the tip. The aim of the work is to benchmark the CFD results with experimental data and to investigate the performance of the turbine using CFD and to with a view to integrating CFD into the design process.     

A review of impulse turbines for wave energy conversion

Oscillating Water Column based wave energy plants convert wave energy into low pressure pnuematic power in the form of bi-directional air flows. Air turbines which are capable of rotating uni-directionally in bi-directional air flow, otherwise also known as self-rectifying turbines, are used to extract mechanical shaft power which is further converted into electrical power by a generator. This paper reviews the state of the art in self-rectifying impulse air turbines. New results on optimum parameters for the fixed-guide-vane impulse turbine are also presented. Starting characteristics and conversion efficiencies of two types of impulse turbines are compared with the well known Wells turbine.     

Application of fluid–structure interaction simulation of an ocean wave energy extraction device

A numerical technique that employs a computational fluid dynamics (CFD) code is used to perform coupled fluid–structure interaction simulation of a wave energy device in order to assess power output in a 3D numerical wave flume. The current method determines the motion of the buoy from the dynamic solution of the fluid flow problem and the dynamic buoy motion problem rather than prescribing the motion of the buoy. The power output of the device is calculated for different wave conditions. The technique was expanded for an array of two buoys to determine the interference between them.