A. Thakker

Effect of blade profile on the performance of a large-scale Wells turbine for wave-energy conversion

The aim of this study is to clarify the effect of rotor blade profile on the performance of the Wells turbine operated at high Reynolds number. In the study, four kinds of blade profile were selected with regard to the blade profile of the Wells turbine. The types of blade profile are as follows: NACA0020, NACA0015, CA9, and HSIM 15-262123-1576. In order to determine the optimum rotor blade profile of the turbine, experimental investigations have been performed for two solidities by model testing and numerical simulation. As a result, it has been concluded that a suitable choice, namely the preferable rotor geometry, is the blade profile of NACA0015. Furthermore, it has been found that the critical Reynolds number of the turbine is around 4×105.

Modeling and scaling of the impulse turbine for wave power applications

This paper addresses the dimensional analysis of experimental data for the impulse turbine and the use of that data to create a model to predict the performance characteristics of any size of turbine under a range operating conditions. The model assumes that the performance of the turbine is a function of flow coefficient only. The model is used to compare the performance of different turbines at the scaled-up level and under varying conditions of axial velocity and angular velocity. Also, the model is used to identify the optimum turbine rotational speed, for maximum output power, at practical sizes over a range of input power levels. This paper discusses issues relating to the sizing and optimum operating point of the impulse turbine over variable sea conditions which oblige the turbine to operate over a design range rather than at a single design point and shows how this optimum operating point may be obtained.

Effects of Compressibility on the Performance of a Wave-Energy Conversion Device with an Impulse Turbine Using a Numerical Simulation Technique

This article presents work carried out to predict the behavior of a 0.6 m impulse turbine with fixed guide vanes as compared with that of a 0.6 hub-to-tip ratio turbine under real sea conditions. In order to predict the true performance of the actual oscillating water column (OWC), the numerical technique was fine-tuned by incorporating the compressibility effect. Water surface elevation versus time history was used as the input data for this purpose. The effect of compressibility inside the air chamber and the turbines performance under unsteady and irregular flow conditions were analyzed numerically. Considering the quasi-steady assumptions, the unidirectional steady-flow experimental data was used to simulate the turbines characteristics under irregular unsteady flow conditions. The results showed that the performance of this type of turbine is quite stable and that the efficiency of the air chamber and the mean conversion efficiency are reduced by around 8% and 5%, respectively, as a result of the compressibility inside the air chamber. The mean efficiencies of the OWC device and the impulse turbine were predicted for 1 month, based on the Irish wave climate, and it was found that the total time period of wave data used is one of the important factors in the simulation technique.

Quasi-Steady Analytical Model Benchmark of an Impulse Turbine for Wave Energy Extraction

This work presents a mean line analysis for the prediction of the performance and aerodynamic loss of axial flow impulse turbine wave energy extraction, which can be easily incorporated into the turbine design program. The model is based on the momentum principle and the well-known Euler turbine equation. Predictions of torque, pressure drop, and turbine efficiency showed favorable agreement with experimental results. The variation of the flow incidence and exit angles with the flow coefficient has been reported for the first time in the field of wave energy extraction. Furthermore, an optimum range of upstream guide vanes setting up angle was determined, which optimized the impulse turbine performance prediction under movable guide vanes working condition.

The effect of rotor geometry on the performance of a Wells turbine for wave energy conversion

SYNOPSIS The paper presents the effect of rotor geometry on the performance of a small-scale Wells turbine for wave energy conversion. In the study, four kinds of blade profile were selected from previous studies with regard to the blade profile of the Wells turbine. The types of blade profile included in the paper are as follows: NACA0020; NACA0015; CA9; and HSIM 15-262123-1576. The experimental investigations have been performed for two solidities by model-testing under steady flow conditions. The effect of blade profile on the running and starting characteristics under sinusoidal flow conditions have been investigated by a numerical simulation using a quasi-steady-state analysis. In addition, the effect of sweep on the turbine characteristics has been investigated for the cases of CA9 and HSIM 15-262123-1576. As a result, a suitable choice of these design factors has been suggested.

Effects of Hub-to-Tip Ratio and Reynolds Number on the Performance of Impulse Turbine for Wave Energy Power Plant

The objective of this paper is to present the performance comparison of the impulse turbines for different diameters. In the study, the investigation has been performed experimentally by model testing for some diameters, especially 0.3 m and 0.6 m. The experiment was performed for Reynolds number range of 0.17 X 105—1.09X 105 and for different values of hub-to-tip ratiov ranging from 0.6 to 0.85. As a result, it was found that the critical Reynolds number is to be around 0.5 X 105 for v=0.6 and 0.4X 105 for v=0.7. For the hub-to-tip ratio, the optimum value is 0.7 when the turbine is operated at lower Reynolds number. However, its value seems to be 0.6 at higher Reynolds number in the tested range.

A 2D Computational Fluid Dynamics Analysis of Wells Turbine Blade Profiles in Isolated and Cascade Flow

This paper deals with the application of Computational Fluid Dynamics (CFD) to the analysis of the aerodynamic characteristics of symmetrical airfoil blades in 2-Dimensional flow. The CFD model was used to compare blades of varying profiles to analyse the aerodynamic forces and the compressibility effects and to compare the differences in modelling the blades in isolated and cascade flow. The model was validated using correction factors with published results for the NACA 0015 blade profile, which show that the model gives good results for the aerodynamic forces. The differences in the predicted aerodynamic characteristics, such as low angle of incidence drag, as well as normal and tangential forces are compared for the isolated and cascade cases. The validated model was then used to compare proposed blade profiles for a Wells Turbine. The paper presents the results of the numerical investigation along with the analysis and comparison of the different profiles.Copyright

Design analysis of 0.6m Impulse turbine with fixed guide vanes for wave energy power conversion

SYNOPSIS 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 the Wells turbine and Impulse turbine with guide vanes, are commonly in use around the world for wave energy power generation. The overall purpose of this research is to perform a complete design analysis of an Impulse turbine with fixed guide vanes for wave energy power generation. The ultimate goal is to optimise the performance of the turbine under actual sea conditions. This research is divided into two phases. First, to design and manufacture a 0.6m diameter Impulse turbine with fixed guide vanes with a new hub to tip ratio; then to validate this design experimentally using Computational Fluid Dynamics (CFD) and to compare the performance characteristics obtained experimentally with those obtained from CFD. The second phase is to optimise turbine blade and guide vane geometry based on theoretical, experimental and CFD analysis and finally, to manufacture and test a 2nd generation turbine, based on this optimum design. This paper presents the work done during the first phase of the research. It reports the design of a 0.6m diameter Impulse turbine with fixed guide vanes, manufacture of turbine blades using a unique method of Rapid Prototyping on a Fused Decomposition Modelling (FDM) machine, experimental analysis of the turbine and comparison of the CFD work with experiment.

A 3D Computational Fluid Dynamics Analysis of the Wells Turbine

This paper deals with the application of Computational Fluid Dynamics (CFD) to the performance comparison of some proposed blade designs for the Well’s Turbine. The turbines were modelled at typical Reynolds numbers for full scale rigs and the results were found to correlate well with scale predictions from experimental data. Three different turbine designs were analysed, one a 4-bladed rotor and the other two 8-bladed rotors. The only difference between the two 8-bladed rotors was the addition of forward sweep to one. The addition of forward sweep was shown to have little effect on the overall performance of the 8-bladed rotor. The 4-bladed rotor was shown to have the highest efficiency and pressure drop at low flow rates, however it was also shown to have a much smaller operating range than the 8-bladed rotors.© 2002 ASME

A Computational Fluid Dynamics Comparison of Wells Turbine Blades in 2D and 3D Cascade Flow

This paper deals with the application of Computational Fluid Dynamics (CFD) to the analysis of the aerodynamic characteristics of symmetrical airfoil blades in 2-Dimensional cascade flow. Theoretical two dimensional cascade analyses of Wells Turbines blade profiles have been used in the past to predict the performance of three-dimensional turbines. The use of two-dimensional cascade models is beneficial as it allows the analysis and optimisation of the blade profile with approximately one tenth the computational requirements of a three-dimensional model. The primary objective of this work was to provide further validation of the use of two dimensional cascade models by comparing the computational predictions with traditional theoretical calculation results and also with three-dimensional turbine results. A secondary objective was to use the two dimensional cascade models to better understand the blade interaction effects that occur in the Wells Turbine. The model was used to analyse and compare three different blade profiles at different cascade settings. This paper presents the results of the numerical investigation, the validation of the results and the subsequent analysis.Copyright