Low-head Turbines Research Articles

Influence of the Blade Hub Geometry on the Performance of Low-Head Axial Flow Turbines

AbstractThe influence of geometric parameters, such as blade profile and hub geometry on axial flow turbines for micro hydro application remains poorly characterized. This paper first introduces a holistic theoretical model for studying the hydraulic phenomenon resulting from geometric modification to the blades. It then describes modification carried out on two runner stages, of which one has untwisted blades and the other has twisted blades obtained by modifying the inlet hub. The experimental results showed that the performance of the untwisted blade runner was satisfactory with a maximum efficiency of 68%. However, positive effects of twisted blades were clearly evident with an efficiency rise of more than 2%. This study also looks into the possible limitations of the model and suggests the extension of the experimental work and the use of computational tools to conduct a progressive validation of all experimental findings, especially on the flow physics within the hub region and the slip phenomena. T...

General overview of the AxialT project: A partnership for low head turbine developments

An overview of the AxialT project is presented. Initiated in 2007 by the Consortium on Hydraulic Machines, the aim of this four years project is to contribute to the study of time-dependent hydraulic phenomena in a propeller turbine. The geometry of the entire turbine is generously shared by all partners. Numerical simulations carried out by all partners are confronted with experimental measurements carried out at the LAMH laboratory in Laval University. A mix of 2D LDA, 3D PIV and unsteady pressure measurements are adapted to yield precise measurements at eight strategic locations within the turbine and for nine operating points. Phase resolved analysis is performed wherever applicable. An illustration of potential analysis accessible with the database is shown for the identification of a vortex in the runner at part load.

Computational study of a low head draft tube and validation with experimental data

The objective of this paper is to investigate methodologies to improve the reliability of CFD analysis of low head turbine draft tubes. When only the draft tube performance is investigated, the study indicates that draft tube only simulations with an adequate treatment of the inlet boundary conditions for velocity and turbulence are a good alternative to rotor/stator (stage) simulations. The definition of the inlet velocity in the near wall regions is critical to get an agreement between the stage and draft tube only solutions. An average turbulent kinetic energy intensity level and average turbulent kinetic energy dissipation length scale are sufficient as turbulence inlet conditions as long as these averages are coherent with the stage solution. Comparisons of the rotor/stator simulation results to the experimental data highlight some discrepancies between the predicted draft tube flow and the experimental observations.

Alternative concept for tidal power plant with reservoir restrictions

The Brazilian North and Northeast regions have possibilities on harnessing tidal power, where the greatest tidal amplitudes are to be found. In the 1970s, a barrage constructed in the Bacanga estuary, a civil construction project for reducing the distance between the city of São Luís do Maranhão and the port of Itaqui, was planned to be the first Brazilian tidal power plant. The favorable conditions associated with the considerable tidal heights, which can be as much as 6.5 m, made this an ideal place for building a pilot plant. Although, a scheme had been proposed to harness tidal energy in a conventional way with the use of the reservoir, the tidal plant in its original form was not implemented due economic and technical restrictions originated from the turbo generators chosen at that time. This paper presents an alternative concept for tidal power plant when the reservoir presents limitations caused by urban occupation, silting up and deterioration of the original structures. These limitations have been verified following the construction of the Bacanga barrage which led to an alternative proposal for the future installation of a pilot tidal power plant. The power generation possible to be harnessed was simulated through a model for each hour from the water head data, outflow, levels, areas and volumes of the reservoir and estuary. The development of the conceptual project, with the utilization of low-head turbines, a floating platform for the turbines and, particularly, taking into consideration those restrictions to be found at the present time, it can be concluded that Bacanga tidal power plant of is technically viable.

An overview of marine renewables in the UK: a synopsis of Michael Hay's presentation

An overview of marine renewables in the UK: a synopsis of Michael Hay's presentation

The tidal-stream energy resource in Passamaquoddy–Cobscook Bays: A fresh look at an old story

The Passamaquoddy–Cobscook Bay archipelago, located near the entrance to the Bay of Fundy where the mean tidal range is 5.7 m, has long been regarded a promising site for tidal-power development. Modern low-head turbines allow power extraction primarily from the kinetic energy of the tidal stream, rather than from the potential energy of an impounded basin, eliminating the need for expensive and elaborate systems of dams, locks and gates. Although the available power levels are much less in streaming applications, the resource may still be significant and accessible in areas with strong tidal flows, because the available power follows the cube of the current speed. The much lower costs per installed kilowatt and the relatively minor environmental impacts warrant a fresh look at the tidal-stream resource. Circulation models indicate that the peak power resource in narrow straits such as Letete Passage and Lubec Narrows exceeds 10 kW/m 2 of installed turbine aperture. In those locations an installation with the surface “footprint” of a typical aquaculture site could produce peak power levels of 1–2 MW under mean tide conditions, and perhaps twice that during spring tides, using modern turbines. Lower power levels are available in deeper, less restricted regions such as Western and Head Harbor Passages. Regions between islands and near headlands where flow speeds exceed about 2 m s −1 (about 4 knots) offer a modest tidal-power potential that could be tapped at relatively low cost and with minimal impact on the environment, fisheries and navigation.

Old watermills—Britain's new source of energy?

Britain's 20 000 disused watermills could be brought back to life as micro-hydrostations generating up to 1000 MW of electricity thanks to a renewed interest in waterwheels, particularly in Germany. Though slightly less efficient than modern low-head turbines, both overshot and undershot waterwheels are much cheaper to build, install and maintain and can operate in a wider range of flow conditions and with a head as little as 0·5 m. Archimedian screws working in reverse have also proved very efficient and durable low-head generators. This paper reviews the latest developments in Germany and the potential for application in the UK.

Old watermills?Britain's new source of energy?

Britain's 20 000 disused watermills could be brought back to life as micro-hydrostations generating up to 1000 MW of electricity thanks to a renewed interest in waterwheels, particularly in Germany. Though slightly less efficient than modern low-head turbines, both overshot and undershot waterwheels are much cheaper to build, install and maintain and can operate in a wider range of flow conditions and with a head as little as 0·5 m. Archimedian screws working in reverse have also proved very efficient and durable low-head generators. This paper reviews the latest developments in Germany and the potential for application in the UK.

Turbine Discharge Measurement by the Velocity-Area Method

Developing the head-power-discharge relationship for a low-head hydroelectric turbine requires accurate measurements of discharge through the unit. Discharge measurements are commonly determined using some type of velocity-area method. The German (DIN) code is used by many utilities. In this paper a densely spaced array of Ott meter data, collected according to the German code, are used to examine the accuracy of this approach. Field data, obtained near the intake entrance (i.e., stoplog guides) of a low-head hydroelectric generating station, show clearly the complex (i.e., nonfully developed) nature of the horizontal flow. Laboratory testing of a scale model suggest that metering the flow close to the entrance of an intake, according to the German code, where the flow is not yet fully developed, will overestimate the discharge by approximately 3%.

1317 低落差用水車吸出し管の圧力回復に及ぼす入口旋回流の影響(O.S.13-5 水力)(O.S.13 自然の流体エネルギー利用技術)

1317 低落差用水車吸出し管の圧力回復に及ぼす入口旋回流の影響(O.S.13-5 水力)(O.S.13 自然の流体エネルギー利用技術)

Acoustic discharge measurements for the performance testing of low-head hydroelectric turbines under disturbed flow conditions

Field performance testing of a low-head hydroelectric turbine is essential to evaluate the efficiency and economics of an operation. For low-head hydroelectric turbines, it is difficult to accurately measure the discharge through a unit. Transit-time velocity measurement technology has recently been used to develop, in a laboratory setting, a unique traversing acoustic discharge meter for low-head hydroelectric applications. This technology was recently combined with Gauss-Legendre quadrature integration as an alternative method of measuring the flow through a low-head hydroelectric turbine. However, laboratory testing of this technology has only dealt with undisturbed or ideal flow conditions. Additional physical modeling has been performed to compare the relative accuracy of the continuous traversing acoustic discharge meter with that of a multilevel Gauss-Legendre quadrature integration in disturbed or nonideal flow conditions. The data indicate that while Gauss-Legendre quadrature may provide more accurate estimates in ideal flow conditions, the continuous traversing acoustic discharge meter is better suited to disturbed flow condition because it can better resolve an intricate velocity profile. The accuracy of this instrumentation is sensitive to relatively large scale vorticity rotating in the plane of the acoustic transducers, although accuracies within 2% are still attainable, which is better than the conventional velocity-area method. Key words: acoustic discharge measurement, disturbed flow, turbine, performance testing.

Acoustic discharge measurements for the performance testing of low-head hydroelectric turbines under disturbed flow conditions

Acoustic discharge measurements for the performance testing of low-head hydroelectric turbines under disturbed flow conditions

Gauss-legendre quadrature estimates of discharge for the performance testing of low-head hydroelectric turbines

The performance testing of low-head hydroelectric turbines is necessary for the efficient and economic operation of a generating station. Of the information required for performance testing, discharge is the most difficult to measure accurately. The velocity-area method is typically used to measure discharge through a low-head plant. Herein the combination of acoustic technology and Gauss-Legendre quadrature (GLq) integration is investigated as an alternative method of measuring discharge. Physical hydraulic modeling was performed to examine the accuracy of discharge estimates associated with different GLq sampling strategies. Data obtained from laboratory testing indicate that the accuracy of estimating discharge increases with the number of GLq levels used. Discharge errors of less than 1% were observed (for undisturbed flow conditions) when 8 or more GLq levels were used.Key words: turbine, performance testing, acoustic discharge measurement, Gauss-Legendre quadrature integration.

Gauss-legendre quadrature estimates of discharge for the performance testing of low-head hydroelectric turbines

Gauss-legendre quadrature estimates of discharge for the performance testing of low-head hydroelectric turbines

A comparison of methods for computing the discharge through hydroelectric turbines

The economic and efficient operation of a hydroelectric generating station requires an accurate description of the head-power-discharge relationship for each turbine. Of the information required to determine this relationship, absolute discharge is the most difficult to measure and the most susceptible to measurement error. For low-head hydroelectric plants, the velocity-area method is often used. This method consists of traversing an array of current meters across the intake to obtain a grid of velocity measurements. The location of the metering points is central to the accuracy of the discharge estimate. The codes governing the performance testing of hydraulic turbines require the metering plane to be located in conditions that cannot be met for low-head hydroelectric plants. In spite of this, the codes are still applied. In this paper a densely spaced array of Ott meter data, collected according to the German (DIN) code, are used to examine the velocity profiles at the entrances of low-head hydroelectric turbine. In addition, these data are interpolated using cubic splines to estimate the time-averaged velocities required to compute discharge according to ASME (PTC-18) code. Interpolated data are also used to examine an alternative method of metering low-head plants based on Gauss-Legendre quadrature integration. The velocity profiles observed are significantly different from those assumed by the German and ASME codes to determine metering locations, which raises questions about the applicability of these codes to low-head plants. The results indicate that a Gauss-Legendre quadrature integration of a 4 × 5 grid of metering points estimates discharge more accurately than the German code, which requires a 7 × 12 grid. The suggestion is the location, and not simply the number of metering points, is central to the accuracy of a discharge estimate through a low-head hydroelectric plant.Key words: low-head hydroelectric turbine, performance testing, head-power-discharge relationship, Ott meter, Gauss-Legendre quadrature integration.

Developing a traversing acoustic discharge measurement technique for the performance testing of low-head hydroelectric turbines

The efficient operation of a hydroelectric generating plant requires an accurate definition of the performance relationships for each turbine-generator unit. Of the information obtained during performance testing, discharge is the most difficult to measure accurately. Acoustic transit-time velocity measurement technology is applied herein to obtain more accurate discharge measurements than current velocity - area method practices. The technique proposed involves continuously traversing a number of acoustic paths, each providing a chordal average velocity measurement, across the turbine intake to obtain a complete integration of the complex velocity profile typical of low-head hydroelectric plants. Data from hydraulic laboratory testing of a single acoustic cell were compared with known flow rates to assess the accuracy and repeatability of the proposed discharge measurement technique. A range of continuous traverse rates was evaluated. The results indicate that the proposed continuous traversing acoustic discharge meter (TADM) can provide efficient, accurate (1-2% error), and repeatable discharge measurements.Key words: turbine, performance testing, acoustic discharge measurement, traversing.

Developing a traversing acoustic discharge measurement technique for the performance testing of low-head hydroelectric turbines

Developing a traversing acoustic discharge measurement technique for the performance testing of low-head hydroelectric turbines

Mortality of Juvenile Clupeids during Passage through a Tidal, Low-Head Hydroelectric Turbine at Annapolis Royal, Nova Scotia

Abstract Migrant juvenile clupeids passing through the tidal, low-head hydroelectric turbine at Annapolis River, Nova Scotia, were monitored during the fall of 1985 and 1986. Although there were two fishways adjacent to both sides of the turbine intake, 98% of the clupeids passed through the tidal-power turbine. Total mortality of clupeids from turbine passage was estimated to be 46.3% for both years combined. Injuries observed were attributed to pressure effects (64.5%), mechanical strike (33.9%), and hydraulic shearing (1.7%).

Flow in open channel near draft tube outlet of low head turbine.

The efficiency of the water turbine is calculated using the static pressure measured on the side wall near the draft tube exit. The pressure decided from the water level just behind the draft tube exit is used if the pressure tap is not installed. Then, in this study, the open channel flow around the draft tube exit is researched experimentally using a model. The main results are obtained as follows. (1) The flow patterns in the open channel can be classified into four types. (2) The condition of the water level rise increasing to the downstream was clarified. (3) The difference between the static pressure head on the draft tube wall near the exit and the water level in the middle of open channel near the draft tube was given. Its maximum value reaches 0.12 V2m/2g for low water levels and wide open channels.

Potential Impact of Large-Scale Tidal Power Developments in the Upper Bay of Fundy on Fisheries Resources of the Northwest Atlantic

Abstract Construction of large-scale, hydroelectric tidal power developments in the upper Bay of Fundy is receiving serious consideration. Potential designs involve ebb-generation with 1400- 5300-MW plants using 7.6 m diameter, straight-flow, low-head turbines installed in dams up to 8 km in length. Discharge through individual turbines will be 400 m3/second at 50 rev/minute with draft tube velocities of 11.4 m/second. Calculated parameters for these turbines are a water length of 2.26 m, impact velocity of 23.99 m/second, blade tip velocity up to 28.7 m/second and a total pressure flux of 1.7 atm. The existing environment is macrotidal (tide range 11–16 m). Embayments are homogeneous estuaries with extremely turbid water. The intertidal biological community is a salt marsh-mudflat biome. The pelagic zone supports large populations of migratory fishes, particularly the alosids, Alosa sapidissima, A. aestivalis, A. pseudoharengus, and Clupea harengus. Striped bass, spiny dogfish, Atlantic salmon, and Atlan...