Application of Numerical Simulation Method to Predict the Performance of Wave Energy Device with Impulse Turbine

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. In order to predict the true performance of the actual Oscillating Water Column (OWC), the numerical technique has been fine tuned by incorporating the compressibility effect. Water surface elevation verses time history based on Pierson Moskowitz Spectra was used as the input data. Standard numerical techniques were employed to solve the non-linear behavior of the sea waves. The effect due to compressibility inside the air chamber and turbine performance under unsteady and irregular flow condition has been analyzed numerically. Considering the quasi-steady assumptions, unidirectional steady flow experimental data was used to simulate the turbine characteristics under irregular unsteady flow conditions. The results show that the performance of this type of turbine is quite stable and efficiency of air chamber and the mean conversion     

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…     

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.     

Effect of guide vane shape on the performance of a Wells turbine

A Wells turbine has inherent disadvantages: lower efficiency and poorer starting characteristics. Providing guide vanes on either side of the rotor could be one of the most effective ways of improving its performance. Several papers have demonstrated the usefulness of 2D guide vanes so far. In order to achieve further improvement in the performance of the Wells turbine, the effect of 3D guide vanes has been investigated experimentally by testing a model under steady flow conditions. Then, the running and starting characteristics under irregular flow conditions have been obtained by a computer simulation using quasi-steady analysis. It is found that the running and starting characteristics of the Wells turbine with 3D guide vanes are superior to those with 2D guide vanes.     

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

This paper presents the experimental results of effect of guide vane shape on performance of an impulse turbine for wave energy conversion. Two types of guide vanes are considered in the present study: two-dimensional (2D) guide vanes and three-dimensional (3D) guide vanes. The previous investigations by the authors revealed that the 2D guide vanes cause large recirculation zones at leading edge of downstream guide vanes, which affect the performance of turbine considerably. In order to improve the performance of turbine, three-dimensional guide vanes are designed based on free-vortex theory. Detailed aerodynamic and performance tests have been conducted on impulse turbine with the two types of guide vanes. The experiments have been conducted under various inlet conditions such as steady, sinusoidal and random (real Sea) flows. From the results, it was proved that the efficiency of impulse turbine has been improved for 4.5% points due to 3D guide vanes. The hysteric characteristic has been noticed from the experimental results of impulse turbine with sinusoidal and random flow inlet conditions. Furthermore, it was investigated that the performance of turbine is considerably more during deceleration of inlet flow than the acceleration in a half cycle of sinusoidal wave.     

Performance estimation of bi-directional turbines in wave energy plants

Oscillating water column(OWC)based wave energy plants have been designed with several types of bidirec-tional turbines for converting pneumatic power to shaft power.Impulse turbines with linked guide vanes andfixed guide vanes have been tested at the Indian Wave Energy plant.This was after initial experimentation withWell's turbines.In contrast to the Well's turbine which has a linear damping characteristic,impulse turbines havenon-linear damping.This has an important effect in the overall energy conversion from wave to wire.Optimizingthe wave energy plant requires a turbine with linear damping and good efficiency over a broad range of flow co-efficient.This work describes how such a design can be made using fixed guide vane impulse turbines.The In-dian Wave Energy plant is used as a case study.     

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.     

Effect of Guide Vanes on the Performance of a Variable Chord Self—Rectifying Air Turbine

INTRODUCTIONWiththeconventionalenergyresourceslikelytogetexhaustedinafewdecades,theinexhaustiblesourcesofenergyhavetotaketheirplace.Alternateenergyfromtheoceanisattractingtheattelltionoftheresearchersinrecentyearsduetoitsperennialavailabilityandminimumhealthhazards.Ofthemanypossibleformsofoceanenergy,waveenergyispromising.Waveenergyisanalternateformenergy,whichispollutantfreeandinnearfutureitislikelytobeeconomicallyviable.Countrieswhicharesurroundedbyseaandpossessremotelysituatedislandcom…     

Performance of an impulse turbine with fixed guide vanes for wave power conversion

A simple fixed geometry impulse turbine has been studied as a suitable power converter in Oscillating Water Column based wave power plants. Comparison with the Wells turbine, which is the commonly used self-rectifying turbine in such applications, shows it to be superior in performance under irregular flow conditions. Optimum guide vane angle for maximum efficiency has been arrived at based on the five angles tested.     

The performance of Wells turbine under bi-directional airflow

This paper presents the performance of a Wells turbine operating under unsteady bi-directional airflow conditions. In this study, four kinds of blade profile were selected, NACA0020, NACA0015, CA9 and HSIM 15-262123-1576. The experiments have been carried out for two solidities under sinusoidal and irregular unsteady flow conditions based on Irish waves (Site2). It was found that for a Wells turbine operating under bi-directional air flow, the rotor geometry preferred is the blade profile of CA9 with rotor solidity σ=0.64. In addition, the efficiency curve of the Wells turbine under unidirectional flow conditions fails to present the rapid rise in the instantaneous efficiency which occurs at low flow coefficient of bi-directional flow condition. A comparative analysis between the numerical simulation results and experimental results was carried out. As a result, an excellent agreement was found between the numerical and experimental results. In addition, the effect of blade profile and rotor solidity on hysteretic characteristics of the turbine has been clarified experimentally under bi-directional airflow.     

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.     

Performance of Wells Turbine with Guide Vanes for Wave Energy Conversion

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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.     

Forced responses on a radial turbine with nozzle guide vanes

Radial turbines with nozzle guide vanes are widely used in various size turbochargers. However, due to the inter- ferences with guide vanes, the blades of impellers are exposed to intense unsteady aerodynamic excitations, which cause blade vibrations and lead to high cycle failures （HCF）.Moreover, the harmonic resonance in some frequency regions are unavoidable due to the wide operation conditions. Aiming to achieve a detail insight into vibration characteristics of radial flow turbine, a numerical method based on fluid .structure interaction （FSI） is presented. Firstly, the unsteady aerodynamic loads are determined by computational fluid dynamics （CFD）.And the fluctuating pressures are transformed from time domain to frequency domain by fast Fourier-transform （FFT）. Then, the entire rotor model is adopted to analyze frequencies and mode shapes considering mistuning in finite element （FE） method. Meanwhile, harmonic analyses, applying the pressure fluctuation from CFD, are conducted to investigate the impeller vibration behavior and blade forced response in frequency domain. The prediction of the vibration dynamic stress shows acceptable agreement to the blade actual damage in consistent tendency.     

Transient numerical analysis of rotor–stator interaction in a Francis turbine

Pressure fluctuation due to rotor–stator interaction and occurrence of vortex rope in draft tube at partial load operation are obvious phenomena in Francis type reaction hydro turbines. These hydrodynamic effects are important issues and should be addressed during the design of hydraulic machines. A 3-dimensional transient state turbulent flow simulation in the entire flow passage of a 70 kW-Francis turbine having specific speed of 203.1 is conducted to investigate the rotor–stator interaction by adopting kω based SST turbulence model. The commercial 3D Navier–Stokes CFD solver Ansys-CFX is utilized to study the flow through this vertical shaft Francis turbine in its stationary and transient passages, at 100% optimum load and 72% of part load. The investigated turbine consists of a spiral casing with 16 guide vanes, 8 stay vanes, a runner with 13 blades and a draft tube. With a time step of 2° of a rotational period of the runner for 10 full rotations, the time dependent pressure and torque variations are monitored at the selected locations during the unsteady state calculation. A periodical behavior is observed for the pressure distribution in guide vanes, runner blades and torque in the runner blades. The pressure distribution curve in runner blades reveals the two dominating frequencies – the lower peaks due to runner speed and the upper peaks corresponding to the number of guide vanes interacting with the flow. The flow acceleration toward inside of the runner is depicted by the expanding wakes behind the stay vanes. Vortex rope is observed in draft tube, downstream the runner, at part-load operation.     

Experimental and computational analysis on guide vane losses of impulse turbine for wave energy conversion

This paper deals with the detailed flow analysis of impulse turbine with experimental and computed results for wave energy power conversion. Initially, several turbulence models have been used in two-dimensional (2-D) computational fluid dynamic (CFD) analysis to find a suitable model for this kind of slow speed unconventional turbine. Experiments have been conducted to validate the CFD results and also to analyze the aerodynamics at various stations of the turbine. The three-dimensional (3-D) CFD model with tip clearance has been generated to predict the internal flow and to understand the effect of tip clearance leakage flow on behavior of the turbine in design and off-design conditions. As a result, it is found from the 2-D results that the comparison between computed and experimental data is good, qualitatively and the turbulence model, standard k–ε can predict the experimental values reasonably well, especially the efficiency of the turbine. Experimental results reveal that the downstream guide vanes are more responsible for low efficiency of the turbine and it is measured that 21% average pressure is lost due to downstream guide vanes. It is proved from the 3-D CFD model with tip clearance that it can predict the experimental values quantitatively and qualitatively. Furthermore, it is estimated from the computed results that the efficiency of the turbine has been reduced about 4%, due to tip clearance leakage flow at higher flow coefficients.     

A novel radial self-rectifying air turbine for use in wave energy converters. Part 2. Results from model testing

The paper presents results from model testing of a self-rectifying radial-flow air turbine, that is being developed as an alternative to the axial-flow self-rectifying turbines for applications in wave energy conversion. In the new machine, named biradial turbine, the flow into, and out of, the rotor is radial. The rotor is surrounded by a pair of radial-flow guide-vane rows. The downstream guide vanes are prevented from obstructing the flow coming out of the rotor by axially displacing the whole guide vane set. The turbine model, with a 0.488 m diameter rotor, was tested in unidirectional flow. Experimental results are shown, in dimensionless form, for efficiency, power and pressure head versus flow rate. They are compared with predictions from CFD computations. The results from model testing were used to estimate the time-averaged efficiency of the turbine subject to the irregular bidirectional air flow induced by random waves.     

Investigation on the forced response of a radial turbine under aerodynamic excitations

Rotor blades in a radial turbine with nozzle guide vanes typically experience harmonic aerodynamic excitations due to the rotor stator interaction. Dynamic stresses induced by the harmonic excitations can result in high cycle fatigue (HCF) of the blades. A reliable prediction method for forced response issue is essential to avoid the HCF problem. In this work, the forced response mechanisms were investigated based on a fluid structure interaction (FSI) method. Aerodynamic excitations were obtained by three-dimensional unsteady computational fluid dynamics (CFD) simulation with phase shifted periodic boundary conditions. The first two harmonic pressures were determined as the primary components of the excitation and applied to finite element (FE) model to conduct the computational structural dynamics (CSD) simulation. The computed results from the harmonic forced response analysis show good agreement with the predictions of Singh's advanced frequency evaluation (SAFE) diagram. Moreover, the mode superposition method used in FE simulation offers an efficient way to provide quantitative assessments of mode response levels and resonant strength.     

Study of turbine with self-pitch-controlled blades for wave energy conversion

The objective of this paper is to clarify the performance of a Wells air turbine using self-pitch-controlled blades under the real sea conditions and to obtain the useful information about the optimum setting angle. Experimental investigations were performed by model testing of a rotor with fixed blades under steady flow conditions. Then, the running and starting characteristics under sinusoidally oscillating flow conditions were obtained by a computer simulation using a quasi-steady analysis. As a result, the performances of the air turbine using self-pitch-controlled blades under the real sea conditions were clarified, and a suitable choice of design factor has been suggested for the setting angle of the rotor.