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.     

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.     

气冷涡轮转子变叶尖间距性能试验及数值研究

为量化评估工程应用的气冷低压涡轮带冠转子叶片的叶尖间距大小对涡轮气动性能的影响,综合现有涡轮部件试验能力,以单级轴流低压涡轮性能试验件为基础,通过控制圆度的机加方式磨削转子外环内壁以实现叶尖间距的变化,采用控制冷气流量比的方法,开展5次不同叶尖间距大小的涡轮级性能试验,得到多工况下涡轮效率、换算流量和换算功率等特性参数。采用加载冷气及考虑转子叶冠结构的数值模型进行三维仿真计算,并与试验结果对比分析。研究表明：叶尖间距由0.6 mm增加至3.2 mm,低压涡轮流通能力增大1%,叶冠泄漏量增多3.4%,但做功能力下降2.3%。涡轮效率变化与叶尖间距大小近似呈线性关系,叶尖间距每增加1 mm,效率约降低0.7%,同时,叶尖间距的增加导致了叶冠腔的旋涡结构、气流掺混及主流入侵强度逐渐增大,引起动叶总压损失的增大,叶尖间距增加至3.2 mm导致叶间位置总压损失由0.88增至2.3。     

Wave energy harvesting using a novel turbine rotor geometry

Wells turbines provide a practical solution for wave energy harvesting. The low aerodynamic efficiency of Wells turbines tangibly reduces their output power. Both the turbine efficiency and output power depend on the turbine solidity. The turbine solidity decreases from rotor hub to rotor tip for the commonly used rotors with constant chord‐length blades. The present work introduces a novel Wells turbine rotor geometry. This geometry was obtained by numerically optimizing the rotor's radial solidity distribution. The turbine performance with different rotor geometries was numerically simulated by solving the three‐dimensional Reynolds‐averaged Navier–Stocks equation under incompressible and steady state flow conditions. Simple and multi‐objective optimization were implemented in order to obtain the optimum rotor geometry. The present work showed that an improved turbine performance can be achieved by optimizing the turbine radial solidity distribution. Two different optimized rotor geometries were obtained and presented. The first rotor geometry improved the turbine efficiency by up to 4.7% by reducing its pressure drop. The second rotor geometries enhanced the turbine output power by up to 10.8%. Copyright © 2016 John Wiley & Sons, Ltd.     

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.     

Power correlation for vertical axis wind turbines with varying geometries

In this paper, a new predictive model that can forecast the performance of a vertical axis wind turbine (VAWT) is presented. The new model includes four primary variables (rotor velocity, wind velocity, air density, and turbine power output) as well as five geometrical variables (rotor radius, turbine height, turbine width, stator spacing, and stator angle). These variables are reduced to include the power coefficient (C_p) and tip speed ratio (TSR). A power coefficient correlation for a novel VAWT (called a Zephyr Vertical axis Wind Turbine (ZVWT)) is developed. The turbine is an adaptation of the Savonius design. The new correlation can predict the turbine's performance for altered stator geometry and varying operating conditions. Numerical simulations with a rotating reference frame are used to predict the operating performance for various turbine geometries. The case study includes 16 different geometries for three different wind directions. The resulting 48 data points provide detailed insight into the turbine performance to develop a general correlation. The model was able to predict the power coefficient with changes in TSR, rotor length, stator spacing, and stator angle, to within 4.4% of the numerical prediction. Furthermore, the power coefficient was predicted with changes in rotor length, stator spacing, and stator angle, to within 3.0% of the numerical simulations. This correlation provides a useful new design tool for improving the ZVWT in the specific conditions and operating requirements specific to this type of wind turbine. Also, the new model can be extended to other conditions that include different VAWT designs. Copyright © 2010 John Wiley & Sons, Ltd.     

New high profitable wind turbines

To generate more quantities of electric energy from wind it is necessary to use a new type of wind turbine built in the regulable mantle's nozzle. This wind turbine type replaces the free air stream from wind by a programmed, i.e. regulated, and partially concentrated stream of air. The nozzle shell is designed as an aerodynamically shaped ring with wings with its lower pressure side pointed towards the centre so that the lift force on each part of the wing is directed radially towards the centre. This induces centrifugal reaction force in the airflow that causes the stream field to expand strongly downstream of the rotor and includes a greater number of streamlines in the active stream in front of the rotor (upstream). Thus the nozzle forces a higher mass flow rate of air through the turbine. The higher mass flow and higher velocity reduction behind the rotor result in a higher energy output from the wind turbine in the nozzle. In this way the wind turbine efficiency is multiplied. New turbines induce more power from weaker and medium winds and their lasting time, because of the relation P=f(v³) (i.e. the power corresponds to wind velocity raised to third power). Wind turbine nozzle produces three times more energy than conventional wind turbine. Short economic analysis for conditions of the island of Lastovo indicates that profit gained by new turbines is up to five times higher than by conventional turbines. The new wind turbine nozzle should generate interest and demand on an international market, even for regions with weaker winds.     

燃气轮机二次空气系统一维传热特性预测

燃气轮机二次空气系统作为冷气在转子内流动的主要流路,关系到转子的强度和冷却气体的分配,对燃气轮机的稳定运行至关重要。针对燃气轮机初步设计的需求,基于基元模型经验公式发展了转子热边界条件分析方法的预测程序。该程序通过模块化二次空气系统,对各基元模型参数化建模,根据流动情况建立相应的流体网络,实现了燃气轮机二次空气系统的传热特性分析。另外以一概念化的二次空气系统的传热特性,验证、分析了该方法能有效、快速地预测二次空气系统的传热特性,为转子的热态分析提供必要条件。     

Numerical analysis of 3-D unsteady flow in a vaneless counter-rotating turbine

To reveal the unsteady flow characteristics of a vaneless counter-rotating turbine (VCRT), a three-dimensional, viscous, unsteady computational fluid dynamics (CFD) analysis was performed. The results show that unsteady simulation is superior to steady simulation because more flow characteristics can be obtained. The unsteady effects in upstream airfoil rows are weaker than those in downstream airfoil rows in the VCRT. The static pressure distribution along the span in the pressure surface of a high pressure turbine stator is more uniform than that in the suction surface. The static pressure distributions along the span in the pressure surfaces and the suction surfaces of a high pressure turbine rotor and a low pressure turbine rotor are all uneven. The numerical results also indicate that the load of a high pressure turbine rotor will increase with the increase of the span. The deviation is very big between the direction of air flow at the outlet of a high pressure turbine rotor and the axial direction. A similar result can also be obtained in the outlet of a low pressure turbine rotor. This means that the specific work of a high pressure turbine rotor and a low pressure turbine rotor is big enough to reach the design objectives. Translated from Journal of Engineering Thermophysics, 2006, 27(1): 35–38 [译自: 工程热物理学报]     

Modelling of the flow at the rotor disc in a geothermal turbine of 110 MW

To elucidate an excessive erosion damage produced by solid particles in the fourth stage rotor disc of a 110 MW double flow geothermal turbine, a bi-dimensional modelling investigation has been conducted. The study was based on a set of results from a computational model using a Reynolds stress, RSM, turbulence model. The predicted results confirmed characteristic flow conditions that may play a main role in the serious erosion of the fourth stage rotor disc governor side, which has been detected in periodic overhauls. The results show a jet of vapour that hits the disc transition radius surface at velocities around 112 m/s. These conditions are produced by the flow outgoing from the labyrinth seal, which passes through a drastic cross-section reduction in the last seal strip. The flow was then simulated introducing specific changes to the geometry and the grid in order to modify the flow patterns favourably. Actually, the suggested changes have been envisaged indeed to be practically feasible of being implemented. The new results showed that it is possible to reduce the erosion process up to 86% by increasing the distance from the labyrinth seal to the rotor disc, which produces a 38% velocity reduction of the vapour flow in that zone. The design proposed in this work produces a flow pattern of a lower velocity on disc surface together with a modified angle of flow incidence. Furthermore, the proposed design also reduces a recirculating flow at the exit of the last seal strip. Based on these results, an analysis of erosion against velocity demonstrates that the redesigned rotor disc proposed here leads to the duplication of the time period used at present between maintenance repairs.     

Sound propagation through the wake flow of a hilltop wind turbine—A numerical study

The sound propagation from a wind turbine situated on the top of a hill into the downwind domain is studied by numerical simulations for 13 cases with varying hill geometry and inflow conditions. The influence of the hill on the atmospheric flow and the wake due to the rotor are simulated by precursory large‐eddy simulations. In addition to the combined consideration of hill and turbine wake effects, these effects are also separately evaluated. The results show that placing the turbine on top of a hill leads to slightly lower sound levels on the downwind plane, although the wake alone supports downward refraction and tends to increase the sound impact near the ground at greater distance. Variations of the hill geometry and the inflow conditions do not have significant effects on the near‐ground sound levels in the downwind domain.     

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.     

Modelling of the flow at the last stage blade tenon in a geothermal turbine using renormalization group theory turbulence model

A bi-dimensional modelling investigation of the flow in the last stage of a 110 MW geothermal turbine has been conducted. The study was based upon a Renormalization Group Theory turbulence model. The results confirmed the existence of flow conditions which may play a main role in the erosion of the L-0 stage blade tenon, which had been detected in periodic overhauls. According to predicted results the relationship between erosion and flow patterns might exist due to: (1) a vapour jet hitting directly on tenon surface at velocities around 65 m/s; (2) a low-pressure region identified with recirculating flow, which may be causing cavitation on the damaged surface. Afterwards, the flow was simulated with changes on the geometry and grid. These changes are, indeed, practically feasible of being implemented. The simulations showed that it is possible to reduce the erosion process by enlarging a flat region close to the L-0 rotor stage. Namely, this change of geometry produces a flow pattern that diminishes the strength of recirculation flow making it possible to reduce both the flow rate through tenon region and its velocity on tenon surface. The pressure drop diminishes as well, clearly reducing a risk of cavitation.     

Numerical analysis of erosion of the rotor labyrinth seal in a geothermal turbine

Excessive erosion of the labyrinth seal of a 110 MW geothermal turbine has been investigated. This study used computational fluid dynamics (CFD) and aims to identify one cause of erosion and a possible solution for substantially reducing it. The predictions were based upon a numerical calculation using a CFD model of the labyrinth seal with a water/steam flow containing hard solid particles and solved with a commercial CFD code: Fluent V5.0. The results confirmed the existence of flow conditions that play a major role in the rotor labyrinth seal erosion. Afterwards, the flow path was simulated with changes of rotor labyrinth seal geometry, which are indeed feasible of being implemented. The results confirmed that it is possible to reduce the erosion process by approximately 80% by incorporating a steam flow deflector in the fourth stage diaphragm, which changes the steam flow direction in the inlet zone to the rotor labyrinth seal channel, resulting in a reduction in steam volumetric mass flow and hard particle velocity by about 44%.     

Numerical modeling of gland seal erosion in a geothermal turbine

Excessive erosion of the low-pressure rotor end gland seal of a 25 MWe geothermal turbine produced a partial loss of turbine vacuum that degraded cycle efficiency. This study used computational fluid dynamics (CFD) to identify the causes of erosion and the optimal steam seal system flow conditions for reducing the erosion problem. The predictions were based upon a numerical calculation using a commercial CFD code (Adapco Star-CD) to model the rotor end gland seal with a steam flow containing hard solid particles. The results confirmed that flow conditions play a major role in rotor gland seal erosion. By changing steam seal flow pressures to vary flow, it was confirmed that there is a threshold seal flow condition below which erosion does not occur, or is minimized. Optimizing the rotor end gland seal supply pressure and intercondenser pressure reduced the turbulent flow kinetic energy by 49%, with a corresponding decrease in the erosion rate of the rotor gland seal surface. The erosion rate is related directly to the particle velocity and turbulent flow kinetic energy. Recommendations are provided for adjusting the rotor end gland seal system to avoid erosion.     

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

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

Performance investigation of a power augmented vertical axis wind turbine for urban high-rise application

A shrouded wind turbine system has a number of potential advantages over the conventional wind turbine. A novel power-augmentation-guide-vane (PAGV) that surrounds a Sistan wind turbine was designed to improve the wind rotor performance by increasing the on-coming wind speed and guiding it to an optimum flow angle before it interacts with the rotor blades. The integration of the PAGV into the 3-in-1 wind, solar and rain water harvester on high-rise buildings has been illustrated. A particular concern related to public safety is minimized when the wind turbine is contained inside the PAGV and noise pollution can be reduced due to the enclosure. Besides, the design of the PAGV that blends into the building architecture can be aesthetic as well. Moreover, a mesh can be mounted around the PAGV to prevent the bird-strike problem. From the wind tunnel testing measurements where the wind turbine is under free-running condition (only rotor inertia and bearing friction were applied), the wind rotor rotational speed (with the PAGV) was increased by 75.16%. Meanwhile, a computational fluid dynamics (CFD) simulation shows that the rotor torque was increased by 2.88 times with the introduction of the PAGV. Through a semi-empirical method, the power output increment of the rotor with the PAGV was 5.8 times at the wind speed of 3 m/s. Also, the flow vector visualization (CFD) shows that a larger area of upstream flow was induced through the rotor with the PAGV.     

用于发电系统的局部进气跨声速涡轮气动设计和优化

为了解决高速机载涡轮发电系统效率较低的问题,通过一维计算和三维数值模拟相结合的方法,对以拉法尔喷管作为静叶、三维叶片作为动叶的局部进气跨声速涡轮级进行了研究。在对原型涡轮级流场分析后,通过ISIGHT优化软件集成NX,NUMECA和ANSYS等模块,采用多岛遗传算法,以喷管扩张角、扩张部分长度、周向排布角度以及动叶叶片进口几何角、出口几何角和轴向弦长作为优化变量对涡轮级进行了优化设计。最终得到给定设计工况下的最优几何参数。优化结果表明：优化得到的涡轮级功率达到了74 530 W,效率达到了79.60%,较原型提升了5.1%。     

Estimating the angle of attack from blade pressure measurements on the National Renewable Energy Laboratory phase VI rotor using a free wake vortex model: yawed conditions

Wind turbine design codes for calculating blade loads are usually based on a blade element momentum (BEM) approach. Since wind turbine rotors often operate in off‐design conditions, such as yawed flow, several engineering methods have been developed to take into account such conditions. An essential feature of a BEM code is the coupling of local blade element loads with an external (induced) velocity field determined with momentum theory through the angle of attack. Local blade loads follow directly from blade pressure measurements as performed in the National Renewable Energy Laboratory (NREL) phase IV campaign, but corresponding angles of attack cannot (on principle) be measured. By developing a free wake vortex method using measured local blade loads, time‐dependent angle of attack and induced velocity distributions are reconstructed. In a previous paper, a method was described for deriving such distributions in conjunction with blade pressure measurements for the NREL phase VI wind turbine in axial (non‐yawed) conditions. In this paper, the same method is applied to investigate yawed conditions on the same turbine. The study considered different operating conditions in yaw in both attached and separated flows over the blades. The derived free wake geometry solutions are used to determine induced velocity distributions at the rotor blade. These are then used to determine the local (azimuth time dependent) angle of attack, as well as the corresponding lift and drag for each blade section. The derived results are helpful to develop better engineering models for wind turbine design codes. Copyright © 2008 John Wiley & Sons, Ltd.     

Multiple streamtube approximation of flow‐induced forces on a Savonius wind turbine

This paper develops a new approximate model to predict the pressure and momentum forces on a Savonius‐style vertical axis wind turbine. Flow distributions through and around the turbine are examined for analytical predictions of the torque and power output, at all rotor angles. A new approximate streamtube method is developed to predict the momentum, lift, and drag forces on the rotor surfaces by the air stream on the basis of an integral force balance on the turbine blades. Unlike other past analytical methods, the technique predicts both momentum and pressure forces imposed on the rotor surface during operation. The calculated results are validated against experimental data and numerical predictions from computational fluid dynamics. Copyright © 2012 John Wiley & Sons, Ltd.