A Study on Fluidic Diode for Wave Energy Conversion-Effect of Bypass Geometry on the Turbine Performance

A twin-impulse turbine for bi-directional flow has been developed for wave energy converter. However, the previous studies elucidated that the mean efficiency of the twin turbine is much lower than that of the impulse turbine for a unidirectional flow because a portion of airflow passes through the reverse flow turbine whose efficiency is very low. Therefore, a fluidic diode was adopted in the twin-impulse turbine in order to reduce the air flow through the reverse flow turbine. In this study, the rectification effect of the fluidic diode was investigated where a bypass is introduced into a blunt body. A computational fluid dynamics (CFD) analysis was conducted to investigate the effect of fluidic diodes on the turbine performance. In this analysis, RANS equations were used as the governing equations and the standard k-ε model was used as the turbulence model. The computational domain is composed of a circular tube and fluidic diode, and the domain meshed with an approximately 1.5 million mesh elements. As a result, it was found that the rectification effect of the fluidic diode is enhanced by installing a blunt body with a bypass hole of 5° taper angle.

Micro T-Mixer with Baffles: Effect of Baffle Height and Setting Angle on Mixing

Chaotic mixing in eight different types of micro T-mixer flow has been studied experimentally and numerically. The present experimental study was performed to visualize two-liquid flows in a micro T-mixer with baffles. The Reynolds number, baffle height and setting angle were varied to investigate their effect on the mixing performance. Three micro T-mixer models were produced, which are several centimeters long and have a rectangular cross-section of few millimeters a side. The mixing of two-liquid was measured using the laser induced fluorescence (LIF) technique. Moreover, three-dimensional numerical simulations were conducted with the open-source CFD solver, OpenFOAM, for the same configuration as used in the experiments to investigate the detailed mechanism of the chaotic mixing. As a result, it was found that the mixing of two-liquid is greatly improved in the micro T-mixer with baffle. The baffle height and setting angle show a significant influence on the mixing performance.

A Twin Unidirectional Impulse Turbine for Wave Energy Conversion—Effect of Fluidic Diode on the Performance

As a system using a conventional unidirectional air turbine in oscillating water column (OWC) based on a wave energy plant, a twin unidirectional impulse turbine topology has been suggested in previous studies. However, the average efficiency of the suggested twin turbine is considerably lower than that of a conventional unidirectional turbine in this topology because reciprocating air flow can’t be rectified adequately by a unidirectional turbine. In order to improve the efficiency, using fluidic diode is discussed. In this study, two different fluidic diodes were discussed by computational fluid dynamics (CFD) and a wind tunnel test. Further, its usefulness is discussed from a view point of the turbine efficiency. The fluidic diode was shown to improve rectification of the topology. However, it needs more improvement in regards to its energy loss in order to enhance the turbine efficiency.

Wells Turbine for Wave Energy Conversion —Improvement of the Performance by Means of Impulse Turbine for Bi-Directional Flow

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.

A Counter-Rotating Impulse Turbine for Wave Energy Conversion

Wave energy can be converted to the electrical energy by using a wave energy converter. The wave energy converter with oscillating water column (OWC) is one of the most promising devices because of its simple structure and easy maintenance. In this device, an oscillating water column due to the wave motion is used to drive an air column. An air turbine is used to convert the pneumatic energy of this bi-directional airflow into the mechanical energy. The counter-rotating impulse turbine for wave energy conversion has been proposed and tested so far, and the average efficiency has been shown to about 0.3. On the contrary, in another offshore experiment, it has been reported that the power generation efficiency of this turbine is larger than Wells turbine in case of small waves. However, there is a scarcity of the detailed characteristics data of counter-rotating impulse turbine. In a previous study, the authors investigated the effect of rotor blade solidity and setting angle of guide vane on the performance of this turbine, and they clarified that the efficiency of this turbine is higher than impulse turbine with single rotor in the range of high flow coefficients. The present study aimed to investigate the effect of rotor blade profile on the turbine performance by using the computation fluid dynamic (CFD) analysis. The inner and outer angles of turbine rotor blade are changed in the range of 50° to 70°. The commercial CFD software of SCRYU/Tetra of Cradle Co. Ltd. was used in the present work. The Reynolds averaged Navier-Stokes (RANS) equations were used as the governing equations and the low Reynold’s number SST k-ω model was used to predict the turbulent stresses. As a result, it was found that the inner angle of γ = 70° and the outer angle of γ = 60° of the turbine rotor blades can give the best turbine efficiency and it shows the efficiency close to the impulse turbine with single rotor, even in the range of low flow coefficients.

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 each other. However, the effect of guide vane solidity on the turbine characteristics has not been clarified to date. The performances of a uni- directional impulse turbine under steady flow conditions were investigated experimentally by using a wind tunnel with large piston/cylinder in this study. Then, mean efficiency of the twin impulse turbine in bidirectional airflow has been estimated by a quasi-steady analysis using experimental results in order to investigate the effect of guide vane solidity on the performance.

Experimental Investigation on a Fixed Oscillating Water Column with an Impulse Turbine for Wave Energy Conversion

A fixed oscillating water column(OWC)-type wave energy converter consists of an air chamber,an air turbine and a generator.The energy conversion processes are the primary conversion in an air chamber and the secondary conversion of the turbine.For the practical use,it is necessary to develop a design method which can consider the incident wave motion,the motion of the internal free surface affected in the structure such as a partly submerged wall,the fluctuation of air pressure in an air chamber,and the rotation of the air turbine.At here,the authors carried out the wave tank tests using the model OWC equipped with the impulse turbine and a generator to obtain the experimental data needed to make this design method.As the result,the efficiencies of the three cases with different speed ratio between generator and turbine,and the effects of the curtain wall depth and the wave length on the energy conversion performance were clarified.

Effect of Fluidic Diode on Performance of Unidirectional Impulse Turbine

A pair of unidirectional turbines(UT)can operate in oscillatory airflow without additional units.However,this arrangement suffers from poor flow rectification.A fluidic diode(FD)offers variable hydrodynamic resistance based on the flow direction,and this can be coupled with UT to improve flow rectification.In this work,a numerical investigation on the effect of FD with UT is presented using the commercial fluid dynamics software ANSYS Fluent 16.1 with k-ωSST turbulence closure model.Periodic domains of UT and FD are numerically validated individually with experimental results.Later,both are coupled to obtain the combined effect,and these results are compared with the analytical approach.It was observed that coupling FD with UT improved the unit's performance at the lower flow coefficient(<1),but its performance decreased as the flow coefficient increased.Due to the diode's presence,fluid leaving the turbine experiences higher resistance at a higher flow coefficient,which decreases the overall performance of the combined unit.

A Straight-bladed Vertical Axis Wind Turbine with a Directed Guide Vane Row-Effect of Guide Vane Geometry on the Performance-

The objective of this study is to show the effect of guide vane geometry on the performance. In order to overcomethe disadvantages of vertical axis wind turbine, a straight-bladed vertical axis wind turbine (S-VAWT) witha directed guide vane row has been proposed and tested by the authors. According to previous studies, it wasclarified that the performance of the turbine can be improved by means of the directed guide vane row. However,the guide vane geometry of S-VAWT has not been optimized so far. In order to clarify the effect of guide vanegeometry, the effects of setting angle and gap between rotor blade and guide vane on power coefficient and startingcharacteristic were investigated in the experiments. The experimental study of the proposed wind turbinewas carried out by a wind tunnel. The wind tunnel with a diameter of 1.8m is open jet type. The wind velocityis 8 m/s in the experiments. The rotor has three straight blades with a profide of NACA0018 and a chord lengthof 100 mm, a diameter of 0.6 m and a blade height of 0.7 m. The guide vane row consists of 3 arc plates.

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.

PIV Measurements of Flows around the Wind Turbines with a Flanged-Diffuser Shroud

当高效之一由 Ohya 等弯屈汽轮机，有称为“风透镜汽轮机”的凸缘弥漫的笼罩这样的风汽轮机被开发。以便调查流动特征和流动加速，纸论述流动速度大小一长类型并且紧缩类型的风有由粒子图象 velocimetry 的凸缘弥漫的笼罩的汽轮机。在长类型风汽轮机的情况中，内部流动的速度向量回答为汽轮机片旋转和旋转的没有片更弥漫在雷纳兹数字被介绍， 0.9 × 1 05。而且，流动回答在之间有或没有旋转被比较。通过 PIV 测量结果，一个人能认识到旋转的汽轮机片是影响在内部墙附近压制骚乱和流动分离更弥漫。时间平均速度向量在即时速度数据的一般水准上被做。在下游的区域有二个大旋涡更弥漫。在凸缘后面的一个旋涡是行动吸在风中到更弥漫并且提起入口流动速度。另一个大旋涡出现在 downstream。它可能作为主要流动的阻塞旋涡是行为。大阻塞旋涡不在即时速度向量是清楚的，然而，它在时间一般水准流动地里清楚地存在。在有紧缩类型的凸缘弥漫的笼罩的风汽轮机附近的流动地也被调查。在紧缩类型的汽轮机的凸缘后面的流动模式与长类型的一样。它意味着流动加速的效果被不稳定的旋涡在凸缘后面引起。有南方的时间一般水准的 CFD 和 PIV 结果的比较优化在以后紧缩类型更弥漫也被介绍。

Impulse Turbine with 3D Guide Vanes for Wave Energy Conversion

在这研究，为波浪精力变换与固定指南翼推进一台推动汽轮机的表演的改进以便完成，表演上的指南翼形状的效果被实验调查。调查被模型在稳定的流动状况下面测试执行。作为结果，因为转矩的增加，有 3D 指南翼的汽轮机的效率比有 2D 指南翼的汽轮机的稍微优异，这被发现指南翼，尽管越过为 3D 案例的汽轮机的压力落下为 2D 案例比那稍微高。关键词液体机械 - 推动汽轮机 - 指南翼 - 波浪精力变换 CLC 数字

Comparison of Performances of Turbines for Wave Energy Conversion

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.

Effect of End Plates on the Performence of a Wells Turbine for Wave Energy Conversion

以便为波浪精力变换改进井汽轮机的表演，汽轮机特征上的结束盘子的效果被模型在稳定的流动条件下面测试试验性地调查了。纳入原来的转子片的尖端的结束板比原来的片侧面稍微大。有结束盘子的井汽轮机的特征与原来的井汽轮机的那些相比，即，没有结束的汽轮机板。作为结果，有结束盘子的井汽轮机的特征比原来的井汽轮机的那些优异，特征依赖于结束板的尺寸和位置，这被结束了。而且，汽轮机表演上的环形的板的效果，它环绕汽轮机并且被纳入尖端，作为一个另外的实验被调查。然而，它的设备不在改进汽轮机特征是有效的。关键词液体机械 - 自然精力 - 井汽轮机 - 结束板 - 波浪精力变换 - 海洋精力 CLC 数字

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 0.6m impulse turbine with fixed guide vanes with 0.6hub-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 ompressibility 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 efficiency is reduced around 8% and 5% respectively,due to compressibility inside air chamber.