Study on an Undershot Cross-Flow Water Turbine

This study aims to develop a water turbine suitable for ultra-low heads in open channels, with the end goal being the effective utilization of unutilized hydroelectric energy in agricultural water channels. We performed tests by applying a cross-flow runner to an open channel as an undershot water turbine while attempting to simplify the structure and eliminate the casing. We experimentally investigated the flow fields and performance of water tur- bines in states where the flow rate was constant for the undershot cross-flow water turbine mentioned above. In addition, we compared existing undershot water turbines with our undershot cross-flow water turbine after at- taching a bottom plate to the runner. From the results, we were able to clarify the following. Although the effec- tive head for cross-flow runners with no bottom plate was lower than those found in existing runners equipped with a bottom plate, the power output is greater in the high rotational speed range because of the high turbine ef- ficiency. Also, the runner with no bottom plate differed from rtmners that had a bottom plate in that no water was being wound up by the blades or retained between the blades, and the former received twice the flow due to the flow-through effect. As a result, the turbine efficiency was greater for runners with no bottom plate in the full ro- tational speed range compared with that found in runners that had a bottom plate.     

PIV measurements of flows around the wind turbines with a flanged-diffuser shroud

The wind turbines with a flanged-diffuser shroud -so called ＂wind lens turbine＂- are developed as one of high performance wind turbines by Ohya et al. In order to investigate the flow characteristics and flow acceleration, the paper presents the flow velocity measurements of a long-type and a compact-type wind turbines with a flanged-diffuser shroud by particle image velocimetry. In the case of the long type wind turbine, the velocity vec- tors of the inner flow field of the diffuser for turbine blades rotating and no blades rotating are presented at Rey- nolds number, 0.9x105. Fur~thermore the flow fields between with and without rotating are compared. Through the PIV measurement results, one can realize that the turbine blades rotating affects as suppress the disturbance and the flow separation near the inner wall of the diffuser. The time average velocity vectors are made on the av- erage of the instantaneous velocity data. There are two large vortices in downstream region of the diffuser. One vortex behind the flange acts as suck in wind to the diffuser and raise the inlet flow velocity. Another large vortex appears in downstream. It might be act as blockage vortex of main flow. The large blockage vortex is not clear in the instantaneous velocity vectors, however it exists clearly in the time average flow field. The flow field around the wind turbine with a compact-type flanged-diffuser shroud is also investigated. The flow pattern behind the flange of the compact-type turbine is the same as the long-type one. It means that the effect of flow acceleration is caused by the unsteady vortices behind the flange. The comparison with CFD and PIV results of meridional time-average streamlines after the compact-type diffuser is also presented.     

Investigation of the performance of a cross-flow turbine

An experimental investigation was conducted to study the effects of some geometric parameters of runners and nozzles (e.g., diameter ratio and throat width ratio) on the efficiency in the cross-flow turbines, by varying of ratio of inner-to-outer diameters of runners and gate openings of two different turbine nozzles under different heads. In this study, four different types of runners (170 mm outer diameter, 114 mm width) were designed and manufactured to investigate the effects of the ratio of inner-to-outer diameters of runners on the turbine efficiency. Each runner had 28 blades and the ratios of inner-to-outer diameters of runners were 0·75, 0·67, 0·58 and 0·54, respectively. The runners were denoted with the numbers 1, 2, 3 and 4, and nozzles A and B. The blade inlet and outlet angles were selected as 30° and 90°. Nozzles A and B were of rectangular cross-sectional channels. Nozzles outlet angles of two solid walls of 16° were measured from the circumferential direction. The performance parameters namely output power, efficiency, runaway speed, reduced speed and power for different nozzle/runner combinations were investigated by changing head range from 8 to 30 m, the nozzle A-runner combinations (A–1, 2, 3, 4) and from 4 to 17 m, the nozzle B-runner combination (B–2) at different gate openings. The results of the present study clearly indicated that there was a negligible difference (e.g., 3% in total between 0·54 and 0·75 diameter ratio) in the efficiency of turbine for different diameter ratios and heads, and that the highest efficiency was obtained as 72% for A–2. © 1998 John Wiley & Sons, Ltd.     

水平轴潮流水轮机转轮尾流特性数值分析

针对潮流水轮机转轮尾流对机组之间水力性能的干扰问题,利用CFD分析软件Fluent对单个水平轴潮流水轮机转轮模型和10倍转轮直径间距下的两台机组模型在额定流速条件下进行三维流场的数值模拟。结果表明,在水轮机转轮旋转平面内不同半径位置处的尾流流速恢复情况明显不同,离旋转轴线越远,尾流流速恢复越快,其流速亏损也越少;当水轮机组之间串列布置,且来流方向与旋转平面垂直情况下,下游机组运行受上游机组转轮的尾流影响较大,应尽量避免该布置方式。     

Performance and wake comparison of horizontal and vertical axis wind turbines under varying surface roughness conditions

A numerical study of both a horizontal axis wind turbine (HAWT) and a vertical axis wind turbine (VAWT) with similar size and power rating is presented. These large scale turbines have been tested when operating stand‐alone at their optimal tip speed ratio (TSR) within a neutrally stratified atmospheric boundary layer (ABL). The impact of three different surface roughness lengths on the turbine performance is studied for the both turbines. The turbines performance, the response to the variation in the surface roughness of terrain, and the most relevant phenomena involved on the resulting wake were investigated. The main goal was to evaluate the differences and similarities of these two different types of turbine when they operate under the same atmospheric flow conditions. An actuator line model (ALM) was used together with the large eddy simulation (LES) approach for predicting wake effects, and it was implemented using the open‐source computational fluid dynamics (CFD) library OpenFOAM to solve the governing equations and to compute the resulting flow fields. This model was first validated using wind tunnel measurements of power coefficients and wake of interacting HAWTs, and then employed to study the wake structure of both full scale turbines. A preliminary study test comparing the forces on a VAWT blades against measurements was also investigated. These obtained results showed a better performance and shorter wake (faster recovery) for an HAWT compared with a VAWT for the same atmospheric conditions.     

Tests on ducted and bare helical and straight blade Darrieus hydrokinetic turbines

Despite much optimistic language on commercial websites, little data is available on actual performance of hydrokinetic turbines. This paper summarises the findings of a series of tests on several Darrieus type cross flow hydrokinetic turbines (HKTs). Although this type of hydrokinetic turbine (HKT) has some advantages over axial flow turbines, fixed pitch Darrieus HKTs also have some drawbacks, including inability to self-start under load, low efficiency and shaking. Variable pitch has been suggested to increase starting torque and efficiency, ducts to increase power output and helical blades to produce smooth torque. To assess each of these modifications, tests were conducted in Australia and Canada on HKTs with fixed and variable pitch straight blades, fixed helical blades, with and without a slatted diffuser, by mounting each turbine in front of a barge and motoring through still water at speeds ranging from less than 1 m/s up to 5 m/s. The diffuser increased the power output by a factor of 3 in one configuration but considerably less in others. A reason for this finding is suggested. The maximum coefficient of performance Cp of the fixed pitch straight blade and helical turbines without a diffuser ranged from about 0.25 at 1.5 m/s down to less than 0.1 at 5 m/s, while Cp for those with a diffuser ranged from about 0.45 down to about 0.3. Fixed blade turbines, both straight and helical, exhibited low starting torque, while variable pitch turbines started easily. Considerable differences in Cp were observed for the same turbine configuration at different speeds. The turbine with fixed pitch, straight blades was found to shake violently due to cyclical hydrodynamic forces on blades, while the helical and variable pitch turbines did not shake excessively. These findings suggest that variable pitch cross flow HKTs should be further investigated.     

基于CFD的二维垂直轴风力机性能计算

采用计算流体力学方法(CFD)针对垂直轴风力发电机,开展简化的二维绕流特性研究。首先,基于开放型转子和增强型转子,研究网格节点数和壁面y+、计算时间步长和湍流模型等的变化对计算结果的影响,对计算模型和方法进行确认。随后,计算分析增强型垂直轴风力机与开放型垂直轴风力机的特性。结果表明,与开放性垂直轴风力发电机相比,增强型垂直轴风力发电机的功率系数和转矩系数有明显增加,且达到最大值的位置向叶尖速比增大的方向移动。然后对增强型垂直轴风力机发电机在不同来流风速下进行计算,发现增强型垂直轴风力发电机的转子转矩随来流风速增加,而转矩系数和功率系数与来流风速无关。最后,针对定子叶片在不同的方向开展计算研究。结果表明,定子叶片在不同方向时,增强型垂直轴风力机的转子转矩不同,且转矩到达峰值的位置也不同;在当前3个方向角中,叶片处于0°方向角时风力机具有最高的转矩系数,即具有最佳的功率系数。     

Experimental Study of Heat Transfer and Pressure Loss in Channels with Miniature V Rib-Dimple Hybrid Structure

Abstract

In order to increase the thermal efficiency, the gas turbines are designed to operate at higher temperature, which requires highly efficient cooling structures for turbine blades. The dimples and ribs are effective surface structures to enhance the convective heat transfer in the gas turbine blade internal cooling. In the present study, a novel hybrid cooling structure with miniature V-shaped ribs and dimples is presented, and the heat transfer and pressure loss characteristics are obtained experimentally. The heat transfer performance of the rib–dimple structures, which include three different rib height-to-hydraulic diameter ratios of 0.017, 0.029 and 0.044 and one dimple configuration with the dimple depth-to-diameter ratio of 0.2, are studied by using the transient liquid crystal thermography technique for turbulent flow in rectangular channels within the Reynolds number range from 10,000 to 60,000. It is found that the miniature V-shaped ribs arranged upstream the dimples can significantly improve the heat transfer performance of the dimples, resulting in a more uniform heat transfer distribution on the surface. The V rib-dimple hybrid structure in the channel shows much higher heat transfer enhancement than the counterparts with only the dimples in the channels.     

Numerical research of cavitation on Francis turbine runners

Francis turbines, as other hydraulic turbines, are custom-designed for nominal operating conditions specific to each power plant. However, they may need to be operated at off-design flow conditions because of variable reservoir levels and flowrates. Operating the turbine at off-design points can cause cavitation. Four cavitation types can be observed on Francis turbine runners. These are leading edge, travelling bubble, draft tube swirl and inter-blade vortex cavitation. They may cause erosion, reduction in efficiency, vibration, instability of operation and noise. Runner blades must be designed taking the flow characteristics into account for design conditions to prevent cavitation. Cavitation limits for the off-design points must also be determined. In this study, the runner geometry of an actual hydroelectric power plant that was designed and implemented in 1960s, is redesigned with the help of the state of the art computational fluid dynamics techniques for cavitation free operation. The cavitation limits for the off-design points are also determined.     

Experimental study of improved HAWT performance in simulated natural wind by an active controlled multi-fan wind tunnel

The effects of turbulent intensity and vortex scale of simulated natural wind on performance of a horizontal axis wind turbine (HAWT) are mainly investigated in this paper.In particular,the unsteadiness and turbulence of wind in Japan are stronger than ones in Europe and North America in general.Hence,Japanese engineers should take account of the velocity unsteadiness of natural wind at installed opden-air location to design a higher performance wind turbine.Using the originally designed five wind turbines on the basis of NACA and MEL blades,the dependencies of the wind frequency and vortex scale of the simulated natural wind are presented.As the results,the power coefficient of the newly designed MEL3-type rotor in the simulated natural wind is 130％ larger than one in steady wind.     

A design methodology for cross flow water turbines

This contribution deals with the design of cross flow water turbines. The mechanical stress sustained by the blades depends on the basic geometrical specifications of the cross flow water turbine, its rotational speed, the exact geometry of the blades and the velocity of the upstream water current. During the operation, the blades are submitted to severe cyclic loadings generated by pressure field's variation as function of angular position. This paper proposes a simplified design methodology for structural analysis of cross flow water turbine blades, with quite low computational time. A new trapezoidal-bladed turbine obtained from this method promises to be more efficient than the classical designs. Its most distinctive characteristic is a variable profiled cross-section area, which should significantly reduce the intensity of cyclic loadings in the material and improve the turbine's durability. The advantages of this new geometry will be compared with three other geometries based on NACA0018 hydrofoil.     

Numerical Investigation of the Interaction between Mainstream and Tip Shroud Leakage Flow in a 2-Stage Low Pressure Turbine

The pressing demand for future advanced gas turbine requires to identify the losses in a turbine and to understand the physical mechanisms producing them. In low pressure turbines with shrouded blades, a large portion of these losses is generated by tip shroud leakage flow and associated interaction. For this reason, shroud leakage losses are generally grouped into the losses of leakage flow itself and the losses caused by the interaction between leak- age flow and mainstream. In order to evaluate the influence of shroud leakage flow and related losses on turbine performance, computational investigations for a 2-stage low pressure turbine is presented and discussed in this paper. Three dimensional steady multistage calculations using mixing plane approach were performed including detailed tip shroud geometry. Results showed that turbines with shrouded blades have an obvious advantage over unshrouded ones in terms of aerodynamic performance. A loss mechanism breakdown analysis demonstrated that the leakage loss is the main contributor in the first stage while mixing loss dominates in the second stage. Due to the blade-to-blade pressure gradient, both inlet and exit cavity present non-uniform leakage injection and extrac- tion. The flow in the exit cavity is filled with cavity vortex, leakage jet attached to the cavity wall and recircula- tion zone induced by main flow ingestion. Furthermore, radial gap and exit cavity size of tip shroud have a major effect on the yaw angle near the tip region in the main flow. Therefore, a full calculation of shroud leakage flow is necessary in turbine performance analysis and the shroud geometric features need to be considered during turbine design process.     

Quantification of wind turbine energy loss due to leading-edge erosion through infrared-camera imaging,numerical simulations,and assessment against SCADA and meteorological data

Quantification of the performance degradation on the annual energy production (AEP) of a wind farm due to leading-edge (LE) erosion of wind turbine blades is important to design cost-effective maintenance plans and timely blade retrofit. In this work, the effects of LE erosion on horizontal axis wind turbines are quantified using infrared (IR) thermographic imaging of turbine blades, as well as meteorological and SCADA data. The average AEP loss of turbines with LE erosion is estimated from SCADA and meteorological data to be between 3% and 8% of the expected power capture. The impact of LE erosion on the average power capture of the turbines is found to be higher at lower hub-height wind speeds (peak around 50% of the turbine rated wind speed) and at lower turbulence intensity of the incoming wind associated with stable atmospheric conditions. The effect of LE erosion is investigated with IR thermography to identify the laminar to turbulent transition (LTT) position over the airfoils of the turbine blades. Reduction in the laminar flow region of about 85% and 87% on average in the suction and pressure sides, respectively, is observed for the airfoils of the investigated turbines with LE erosion. Using the observed LTT locations over the airfoils and the geometry of the blade, an average AEP loss of about 3.7% is calculated with blade element momentum simulations, which is found to be comparable with the magnitude of AEP loss estimated through the SCADA data.     

空冷汽轮机末两级变工况三维流动的数值模拟

采用三维粘性数值模拟方法对变工况下空冷汽轮机末两级流动进行了模拟,研究了效率和脱流高度等重要参数的变化规律,着重分析了设计点和小容积流量工况时的三维流场。通过分析了解了机组在变工况运行时末级流动的特点,为空冷汽轮机末级叫片的设计和优化提供了依据。图8参5     

Prediction of turbine blade heat transfer and aerodynamics using a new unsteady boundary layer transition model

The effects of periodic unsteady flow on heat transfer and aerodynamic characteristics, particularly on the boundary layer transition along the suction and the pressure surfaces of a typical gas turbine blade, are experimentally and theoretically investigated. Comprehensive aerodynamic and heat transfer experimental data are collected for different unsteady passing frequencies that are typical of gas turbines. To predict the effect of the impinging periodic unsteady flow on the heat transfer and the aerodynamics of turbine blades, a new unsteady boundary layer transition model is developed. The model is based on a universal unsteady intermittency function and utilizes an inductive approach that implements the results of comprehensive experimental and theoretical studies of unsteady wake development and the boundary layer flow. Three distinct quantities are identified as primarily responsible for the transition of an unsteady boundary layer: (1) the universal relative intermittency function, (2) maximum intermittency, and (3) minimum intermittency. The analysis of the experimental results and the comparison with the model prediction confirm the validity of the model and its capability to accurately predict the unsteady boundary layer transition.     

试验汽轮机内湿蒸汽测量研究

汽轮机内部的湿蒸汽会对机组的运行效率、动叶片水蚀及机组运行寿命产生重要影响。介绍了国内外对于汽轮机湿蒸汽研究的概况,使用基于多波长消光法与光阻法测量原理结合的湿蒸汽测量集成探针系统,对某汽轮机末级湿蒸汽1次、2次水滴进行了实测研究,介绍了1次水滴与2次水滴的测量方法及数据处理过程,给出了包括1次水滴湿度与2次水滴数目及粒度分布的计算结果。结果表明,沿着叶高1次水滴湿度与2次水滴粒度渐增,而经过运用除湿措施的末级后2次水滴平均粒径减小、粒度分布变窄。     

On applicability of reciprocating flow turbines developed for wave power to tidal power conversion

Tidal power generation with reciprocating turbines in a simple system is investigated on a performance simulation in order to enlarge the capability of practical use of tidal power with extra-low head and time-varying energy density characteristics. Four reciprocating turbines, which are two types of impulse and a Wells developed for wave power conversion systems, and a cross-flow type of Darrieus for extra-low head hydropower are focused for utilizing extra-low head tidal power. Their turbine characteristics in a unidirectional steady flow obtained by physical test models are compared in non dimensional forms and power plant performance with the turbines are numerically simulated on equivalently scaled turbines based on the low of similitude on turbine performance with the non dimensional characteristics under one of the simplest controls in combination with suitable reservoir ponds area. The output of the power plant depends on tidal difference and a pond inundation area. The results are summarized and discussed on the averaged electric output of the power plant and the optimum scale of pond inundation area.     

新型双风轮风力机气动特性的三维流场数值模拟

基于Simplic算法,采用SST κ-ω湍流模型,利用Fluent6．3数值模拟软件对新型的小型双风轮风力机的气动特性进行了三维流场研究,并与同规格单风轮风力机的三维流场进行了比较．结果表明：与单风轮风力机相比,随着后风轮叶片数目的增加,新型双风轮风力机的湍流强度变大,风力机运行的稳定性在一定程度上有所降低;当后风轮的叶片数目合理时,后风轮对前风轮的影响较小,且可以有效地捕捉到前风轮的漏风,使得新型双风轮风力机的风轮在获得较大迎风面积的同时可以保持较高的转速,进而能够高效地实现风能的两级利用,明显提高发电功率和增大风能利用系数．     

脉冲涡轮的性能预测及其特点分析

在准稳定假设的基础上,本文提出了脉冲增压系统中涡轮特性的计算方法。该方法考虑了脉冲条件下涡轮主要损失变化以及在压力波峰处可能出现超临界流动时,涡轮特性的变化。本文计算并分析了在典型的进口参数脉冲波时,径流涡轮和轴流涡轮性能的变化及其特点。     

Influence of blade deformation and yawed inflow on performance of a horizontal axis tidal stream turbine

For a better design of tidal stream turbines operated in off-design conditions, analyses considering the effects of blade deformation and yawed inflow conditions are necessary. The flow load causes deformation of the blade, and the deformation affects the turbine performance in return. Also, a yawed inflow influences the performance of the turbine. As a validation study, a computational fluid dynamics (CFD) simulation was carried out to predict the performance of a horizontal axis tidal stream turbine (HATST) with rigid blades. The numerical uncertainty for the turbine performance with blade deformation and a yawed inflow was evaluated using the concept of the grid convergence index (GCI). A fluid–structure interaction (FSI) analysis was carried out to estimate the performance of a turbine with flexible composite blades, with the results then compared to those of an analysis with rigid blades. The influence of yawed inflow conditions on the turbine performance was investigated and found to be important in relation to power predictions in the design stages.