The Wells turbine is an axial-flow air-turbine designed to extract energy from ocean waves. An important consideration is the self-starting capability of the Wells turbine, a phenomenon encountered where the turbine a...The Wells turbine is an axial-flow air-turbine designed to extract energy from ocean waves. An important consideration is the self-starting capability of the Wells turbine, a phenomenon encountered where the turbine accelerate by itself up to a certain speed for the best turbine performance. In order to clarify the self-starting characteristic and running performance of the Wells turbine in an irregular oscillating flow, a numerical simulation process is established in this paper on the rational assumption of quasi-steady flow conditions, Both self-starting characteristics and running performance are obtained through the numerical simulation and subsequently compared with the experimental data achieved on a computer-controlled oscillating flow test rig which could realize some irregular oscillating flow according to the specified spectrum. Results show that the self-starting time decreases with the increase of the significant wave height and the mean frequency of the irregular oscillating flow, Therefore, it is possible to predict accurately the performance of the Wells turbine by computer simulation.展开更多
Wells turbine has inherent disadvantages in comparison with conventional turbines: relative low efficiency at high flow coefficient and poor starting characteristics. To solve these problems, the authors propose Wells...Wells turbine has inherent disadvantages in comparison with conventional turbines: relative low efficiency at high flow coefficient and poor starting characteristics. To solve these problems, the authors propose Wells turbine with booster turbine for wave energy conversion, in order to improve the performance in this study. This turbine consists of three parts: a large Wells turbine, a small impulse turbine with fixed guide vanes for oscillating airflow, and a generator. It was conjectured that, by coupling the two axial flow turbines together, pneumatic energy from oscillating airflow is captured by Wells turbine at low flow coefficient and that the impulse turbine gets the energy at high flow coefficient. As the first step of this study on the proposed turbine topology, the performance of turbines under steady flow conditions has been investigated experimentally by model testings. Furthermore, we estimate mean efficiency of the turbine by quasi-steady analysis.展开更多
An optimum design of the turbine would need a clear understanding of the influence of blade geometry on a Wells turbine performance. Practically, it is difficult to suggest the optimum geometry for the Wells turbine d...An optimum design of the turbine would need a clear understanding of the influence of blade geometry on a Wells turbine performance. Practically, it is difficult to suggest the optimum geometry for the Wells turbine due to the complex interrelation among important parameters, the solidity, hub-to-tip ratio, aspect ratio, blade sweep of rotor, and so on. In the present study, the effect of blade geometry with the hub-to-tip and aspect ratios of rotor on the turbine performance was investigated with a numerical technique. As a result, the optimum blade geometry is as follows: the hub-to-tip ratio is about 0.7, and the aspect ratio about 0.5 under other constant important parameters, NACA0020 blade with blade sweep ratio of 0.35, and solidity of about 0.67. Furthermore, the detailed flow patterns for blade geometry were also shown and discussed in this paper.展开更多
A Wells turbine for wave power conversion has hysteretic characteristics in a reciprocating flow. The hysteretic loop is opposite to the well-known dynamic stall of an airfoil. In this paper, the mechanism of the hyst...A Wells turbine for wave power conversion has hysteretic characteristics in a reciprocating flow. The hysteretic loop is opposite to the well-known dynamic stall of an airfoil. In this paper, the mechanism of the hysteretic behavior was elucidated by an unsteady 3-dimensional Navier-Stokes numerical simulation. It was found that the hysteretic behavior was associated with a streamwise vortical flow appearing near the blade suction surface. The effects of hub-to-tip ratio and tip clearance on the hysteretic characteristics of the Wells turbine have also been discussed in this paper.展开更多
The Wells turbine for a wave power generator is a self-rectifying air turbine that is available for an energy conversion in an oscillating water-air column without any rectifying valve. The objective of this paper is ...The Wells turbine for a wave power generator is a self-rectifying air turbine that is available for an energy conversion in an oscillating water-air column without any rectifying valve. The objective of this paper is to compare the performances of the Wells turbines in which the profile of blade are NACA0020, NACA0015, CA9 and HSIM15-262123-1576 in the small-scale model testing. The running characteristics in the steady flow, the start and running characteristics in the sinusoidal flow and the hysteretic characteristics in the sinusoidal flow were investigated for four kinds of turbine. As a conclusion, the turbine in which the profile of blade is NACA0020 has the best performances among 4 turbines for the running and starting characteristics in the small-scale model testing.展开更多
The drag characteristics of the Wells turbine are difficult to be accurately predicted because of the influences of many variables. Detailed analyses about the effects of these variables on the drag characteristics ed...The drag characteristics of the Wells turbine are difficult to be accurately predicted because of the influences of many variables. Detailed analyses about the effects of these variables on the drag characteristics educe that the most sensifive parameters to the drag characteristics are the turbine solidity of the turbine and incidence angle of airflow. In this paper, an experimental research is conducted on the pressure drop across the flat- plate rotor which is used to simulate the Wells turbine. After nondimensionalization and fitting of the experimental data, a common experiential formula is obtained. Compared with the experimental data from literature, the computational results are satisfactory. Thus, this report provides a simple and convenient method for predicting the drag characteristics of the Wells turbine and optimizing the match design between an oscillating water column and a chamber.展开更多
Wells turbine is a self rectifying air flow turbine capable of converting pneumatic power of the periodically reversing air stream in Oscillating Water Column into mechanical energy. One of the principal reasons for t...Wells turbine is a self rectifying air flow turbine capable of converting pneumatic power of the periodically reversing air stream in Oscillating Water Column into mechanical energy. One of the principal reasons for the low efficiency of the Wells turbine is its lower tangential force compared to its axial force. Guide vanes before and after the rotor suggest a means to improve the tangential force, hence its efficiency. Experimental investigations are carried out on the Wells turbine with a variable chord (VACR) blade rotor fitted with inlet and outlet guide vanes to understand the aerodynamics especiallyimprovement in efficiency and starting characteristics. Numerical simulation has been made to clarify the unsteady characteristics of the turbine with guide vanes. Studies are done at various flow coefficients covering the entire range of flow coefficients over which the turbine is operable. The efficiency,starting characteristics of the Wells turbine has improved when compared with the turbine without guide vanes.展开更多
In order to improve the performance of a Wells turbine, the effect of guide vanes with various gaps between turbine rotor and guide vane has been clarified by model testing and numerical simulation.The results have be...In order to improve the performance of a Wells turbine, the effect of guide vanes with various gaps between turbine rotor and guide vane has been clarified by model testing and numerical simulation.The results have been compared with those of the case without guide vanes. It is found that the overall characteristics are considerably improved by the inlet guide vanes. Furthermore,a suitable choice of design factor for the gap has been suggested.展开更多
The objective of this paper is to compare the performances of the themes, which could be used for wave energy conversion in the near future, under various irregular wave conditions. The turbines included in the paper ...The objective of this paper is to compare the performances of the themes, which could be used for wave energy conversion in the near future, under various irregular wave conditions. The turbines included in the paper are as follows: (a) Wells turbine with guide vanes; (b) impulse turbine with self-pitch-controlled guide vanes; (c) impulse turbine with fixed guide vanes. In this study, experimental investigations were carried out to clarify the performances of the turbines under steady flow conditions, and then a numerical simulation was used for predicting the performances under irregular wave conditions with various significant wave heights. As a result it was found that the running and starting characteristics of the impulse turbines could be superior to those of the Wells turbine.展开更多
The use of a Savonius rotor as turbine for an oscillating water column(OWC) is demonstrated.The effect of tuning the OWC using turbine duct blockage is also studied for different wave conditions.A horizontal turbine s...The use of a Savonius rotor as turbine for an oscillating water column(OWC) is demonstrated.The effect of tuning the OWC using turbine duct blockage is also studied for different wave conditions.A horizontal turbine section OWC employing a Savonius rotor was tested by varying the opening of OWC exit(0%,25%,50%,75% and 100%) to study the behavior and performance of the device.The OWC model was tested at water depth of 0.29 m at frequencies of 0.8,0.9 and 1.0 Hz while the exit openings are varied.The static pressure,dynamic pressure,rotational speed of the Savonius rotor and the coefficient of power are presented as results.The OWC with exit opening of 25% showed greater performance in terms of rotational speed and CP compared to OWC with other exit opening percentages.This proves the ability of the OWC to be tuned by regulating flow in the turbine duct.展开更多
基金This subject was financially supported by the National Natural Science Foundation of China (Grant No. 59976047)
文摘The Wells turbine is an axial-flow air-turbine designed to extract energy from ocean waves. An important consideration is the self-starting capability of the Wells turbine, a phenomenon encountered where the turbine accelerate by itself up to a certain speed for the best turbine performance. In order to clarify the self-starting characteristic and running performance of the Wells turbine in an irregular oscillating flow, a numerical simulation process is established in this paper on the rational assumption of quasi-steady flow conditions, Both self-starting characteristics and running performance are obtained through the numerical simulation and subsequently compared with the experimental data achieved on a computer-controlled oscillating flow test rig which could realize some irregular oscillating flow according to the specified spectrum. Results show that the self-starting time decreases with the increase of the significant wave height and the mean frequency of the irregular oscillating flow, Therefore, it is possible to predict accurately the performance of the Wells turbine by computer simulation.
文摘Wells turbine has inherent disadvantages in comparison with conventional turbines: relative low efficiency at high flow coefficient and poor starting characteristics. To solve these problems, the authors propose Wells turbine with booster turbine for wave energy conversion, in order to improve the performance in this study. This turbine consists of three parts: a large Wells turbine, a small impulse turbine with fixed guide vanes for oscillating airflow, and a generator. It was conjectured that, by coupling the two axial flow turbines together, pneumatic energy from oscillating airflow is captured by Wells turbine at low flow coefficient and that the impulse turbine gets the energy at high flow coefficient. As the first step of this study on the proposed turbine topology, the performance of turbines under steady flow conditions has been investigated experimentally by model testings. Furthermore, we estimate mean efficiency of the turbine by quasi-steady analysis.
文摘An optimum design of the turbine would need a clear understanding of the influence of blade geometry on a Wells turbine performance. Practically, it is difficult to suggest the optimum geometry for the Wells turbine due to the complex interrelation among important parameters, the solidity, hub-to-tip ratio, aspect ratio, blade sweep of rotor, and so on. In the present study, the effect of blade geometry with the hub-to-tip and aspect ratios of rotor on the turbine performance was investigated with a numerical technique. As a result, the optimum blade geometry is as follows: the hub-to-tip ratio is about 0.7, and the aspect ratio about 0.5 under other constant important parameters, NACA0020 blade with blade sweep ratio of 0.35, and solidity of about 0.67. Furthermore, the detailed flow patterns for blade geometry were also shown and discussed in this paper.
文摘A Wells turbine for wave power conversion has hysteretic characteristics in a reciprocating flow. The hysteretic loop is opposite to the well-known dynamic stall of an airfoil. In this paper, the mechanism of the hysteretic behavior was elucidated by an unsteady 3-dimensional Navier-Stokes numerical simulation. It was found that the hysteretic behavior was associated with a streamwise vortical flow appearing near the blade suction surface. The effects of hub-to-tip ratio and tip clearance on the hysteretic characteristics of the Wells turbine have also been discussed in this paper.
文摘The Wells turbine for a wave power generator is a self-rectifying air turbine that is available for an energy conversion in an oscillating water-air column without any rectifying valve. The objective of this paper is to compare the performances of the Wells turbines in which the profile of blade are NACA0020, NACA0015, CA9 and HSIM15-262123-1576 in the small-scale model testing. The running characteristics in the steady flow, the start and running characteristics in the sinusoidal flow and the hysteretic characteristics in the sinusoidal flow were investigated for four kinds of turbine. As a conclusion, the turbine in which the profile of blade is NACA0020 has the best performances among 4 turbines for the running and starting characteristics in the small-scale model testing.
基金This project was financially supported by the Talent Recruitment Funds of Guangdong Ocean University (Grant No.0512092) and the Key Subject Construction Foundation of Guangdong Ocean University (Grant No.ZD2006004)
文摘The drag characteristics of the Wells turbine are difficult to be accurately predicted because of the influences of many variables. Detailed analyses about the effects of these variables on the drag characteristics educe that the most sensifive parameters to the drag characteristics are the turbine solidity of the turbine and incidence angle of airflow. In this paper, an experimental research is conducted on the pressure drop across the flat- plate rotor which is used to simulate the Wells turbine. After nondimensionalization and fitting of the experimental data, a common experiential formula is obtained. Compared with the experimental data from literature, the computational results are satisfactory. Thus, this report provides a simple and convenient method for predicting the drag characteristics of the Wells turbine and optimizing the match design between an oscillating water column and a chamber.
文摘Wells turbine is a self rectifying air flow turbine capable of converting pneumatic power of the periodically reversing air stream in Oscillating Water Column into mechanical energy. One of the principal reasons for the low efficiency of the Wells turbine is its lower tangential force compared to its axial force. Guide vanes before and after the rotor suggest a means to improve the tangential force, hence its efficiency. Experimental investigations are carried out on the Wells turbine with a variable chord (VACR) blade rotor fitted with inlet and outlet guide vanes to understand the aerodynamics especiallyimprovement in efficiency and starting characteristics. Numerical simulation has been made to clarify the unsteady characteristics of the turbine with guide vanes. Studies are done at various flow coefficients covering the entire range of flow coefficients over which the turbine is operable. The efficiency,starting characteristics of the Wells turbine has improved when compared with the turbine without guide vanes.
文摘In order to improve the performance of a Wells turbine, the effect of guide vanes with various gaps between turbine rotor and guide vane has been clarified by model testing and numerical simulation.The results have been compared with those of the case without guide vanes. It is found that the overall characteristics are considerably improved by the inlet guide vanes. Furthermore,a suitable choice of design factor for the gap has been suggested.
文摘The objective of this paper is to compare the performances of the themes, which could be used for wave energy conversion in the near future, under various irregular wave conditions. The turbines included in the paper are as follows: (a) Wells turbine with guide vanes; (b) impulse turbine with self-pitch-controlled guide vanes; (c) impulse turbine with fixed guide vanes. In this study, experimental investigations were carried out to clarify the performances of the turbines under steady flow conditions, and then a numerical simulation was used for predicting the performances under irregular wave conditions with various significant wave heights. As a result it was found that the running and starting characteristics of the impulse turbines could be superior to those of the Wells turbine.
文摘The use of a Savonius rotor as turbine for an oscillating water column(OWC) is demonstrated.The effect of tuning the OWC using turbine duct blockage is also studied for different wave conditions.A horizontal turbine section OWC employing a Savonius rotor was tested by varying the opening of OWC exit(0%,25%,50%,75% and 100%) to study the behavior and performance of the device.The OWC model was tested at water depth of 0.29 m at frequencies of 0.8,0.9 and 1.0 Hz while the exit openings are varied.The static pressure,dynamic pressure,rotational speed of the Savonius rotor and the coefficient of power are presented as results.The OWC with exit opening of 25% showed greater performance in terms of rotational speed and CP compared to OWC with other exit opening percentages.This proves the ability of the OWC to be tuned by regulating flow in the turbine duct.
