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This paper discusses experiments that were conducted to refine some of the key cross‐flow turbine runner parameters for better performance. The parameters studied were identified by previous studies as key design parameters. The research included narrowing the range of the number of blades, the determination of the impact of the first‐stage exit angle, and the effect of flow stream spreading on the performance of the cross‐flow turbine. The results indicate an optimum number of blades that would produce maximum efficiency of the turbine, and a clear trend of the effect of the first‐stage exit angle and flow stream spreading on the efficiency. For the best nozzle‐runner combination, the maximum efficiency closest to the discharge averaged maximum efficiency is determined to be 92%, with an uncertainty of ±2.4%. This result is an improvement over the reported maximum efficiency of any cross‐flow turbine.

The present paper discusses an experimental investigation of the key parameters influencing cross-flow turbine efficiency. The experiments included measurements of torque, rotational speed, flow rate, and total head in physical models of turbines and nozzles. One physical parameter (flow rate) and six geometric parameters of the turbine were investigated: the angle of water entry to the runner, diameter ratio, number of blades, flow-stream spreading, runner aspect ratio, and blade exit angle. A total of 39 runners and 11 nozzles were tested in 75 different combinations. Analysis performed on the results identified the impact of the different parameters on the turbine efficiency. The results indicate that with careful selection of the cross-flow turbine parameters, efficiencies as high as 88.0% with an uncertainty of [+-]2.4% can be achieved. This is considered an improvement over the claimed maximum efficiency reported in the literature.

The draft tube of a cross-flow turbine uses the difference in level between runner and tail water, especially in the case of low heads, We intented to obtain the desirable profile of a draft tube of a cross-flow turbine and present the effects of water level in the draft tube on the turbine performance. The main results are as follows. (1) The flow velocity in the draft tube is high near both side walls and low at the central part, because the flow which is directed radially outward at the runner exit is restrained by both side walls of the draft tube. (2) In the case of underwater operation of the runner, the vortex flow accompanying the re-entry flow to the runner must be prevented. (3) The optimum ratio of the width of draft tube to the length of nozzle exit arc is nearly 1.6.

An investigation of the flow inside the nozzle of a Cross-Flow turbine, which is a hydraulic turbine where the rectangular water jet issuing from the nozzle crosses the rotor blades twice, is presented here. Part of the investigation consisted in the experimental measurement of the static pressure distribution on the inside walls of two different nozzle configurations, both with the nozzle mounted alone and in the presence of a rotor. The tests performed in the presence of a rotor included the measurement of efficiency and covered a wide range of working conditions around the best efficiency point. The analysis of the results obtained in this way give us an indication of the influence of the turbine non-dimensional volume flow rate on the flow inside the nozzle and the way it affects the reaction degree of the machine and its efficiency level. Although most of the tests were carried out with a 25-blade rotor, one of the analysed nozzle configurations (that with an inside vane) was also tested with a 10-blade rotor, permitting the assessment of the effect the number of blades has on the flow in the nozzle. The flow inside the nozzle with no inside vane was numerically analysed using a method based on a Schwarz-Christoffel conformal transformation of variables. The numerical results show a fair agreement with the experimental data collected when the rotor was not present. A qualitative discussion of some of the losses occurring in the nozzle is advanced based on the computer results, and its conclusions are used for explaining the poor performance of the nozzle with no inside vane.

The internal flow in a cross-flow turbine is nonuniform because the water passes through only part of the runner. Therefore, the unsteady fluid forces act on a blade through rotation. The experimental and theoretical studies for determination of fluid forces on the blade in a cross-flow turbine are conducted. In the experiment, the tangential and radial forces are measured on a test blade using the strain gauges and slip rings. On the other hand, in the theoretical study, they are calculated numerically using the unsteady momentum theory. The calculated results are compared with experimental data and good agreement between them is demonstrated. Furthermore, the maximum forces are found to occur immediately before the blade leaves the nozzle exit in both the experimental and theoretical results.

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.

The mechanical power, total rotor drag, and near-wake velocity of a 1:6 scale model (1.075 m diameter) of the US Department of Energy’s Reference Model vertical-axis cross-flow turbine were measured experimentally in a towing tank, to provide a comprehensive open dataset for validating numerical models. Performance was measured for a range of tip speed ratios and at multiple Reynolds numbers by varying the rotor’s angular velocity and tow carriage speed, respectively. A peak power coefficient CP = 0.37 and rotor drag coefficient CD = 0.84 were observed at a tip speed ratio λ0 = 3.1. A regime of weak linear Re-dependence of the power coefficient was observed above a turbine diameter Reynolds number ReD ≈ 106. The effects of support strut drag on turbine performance were investigated by covering the rotor’s NACA 0021 struts with cylinders. As expected, this modification drastically reduced the rotor power coefficient. Strut drag losses were also measured for the NACA 0021 and cylindrical configurations with the rotor blades removed. For λ = λ0, wake velocity was measured at 1 m (x/D = 0.93) downstream. Mean velocity, turbulence kinetic energy, and mean kinetic energy transport were compared with results from a high solidity turbine acquired with the same test apparatus. Like the high solidity case, mean vertical advection was calculated to be the largest contributor to near-wake recovery. However, overall, lower levels of streamwise wake recovery were calculated for the RM2 case—a consequence of both the relatively low solidity and tapered blades reducing blade tip vortex shedding—responsible for mean vertical advection—and lower levels of turbulence caused by higher operating tip speed ratio and therefore reduced dynamic stall. Datasets, code for processing and visualization, and a CAD model of the turbine have been made publicly available.

The near-wake of a vertical-axis cross-flow turbine (CFT) was modeled numerically via blade-resolved $k$-$\omega$ SST and Spalart-Allmaras RANS models in two and three dimensions. Results for each case are compared with experimental measurements of the turbine shaft power, overall drag, mean velocity, turbulence kinetic energy, and momentum transport terms in the near-wake at one diameter downstream. It was shown that 2-D simulations overpredict turbine loading and do not resolve mean vertical momentum transport, which plays an important role in the near-wake's momentum balance. The 3-D simulations fared better at predicting performance, with the Spalart-Allmaras model predictions being closest to the experiments. The SST model more accurately predicted the turbulence kinetic energy while the Spalart-Allmaras model more closely matched the momentum transport terms in the near-wake. These results show the potential of blade-resolved RANS as a design tool and a way to "extrapolate" experimental flow field measurements., Comment: 22 pages, 12 figures

An experimental investigation was conducted to study the effect of some geometric parameters on the efficiency of the cross-flow turbine. Turbine models were constructed with three different numbers of blades, three different angles of water entry to the runner, and three different inner-to-outer diameter ratios. Nozzles were also constructed for the experiments to match the three different angles of water entry to the runner. A total of 27 runners were tested with the three nozzles. The results of the experiments clearly indicated that efficiency increased with increase in the number of blades. Moreover, it was determined that an increase in the angle of attack beyond 24 deg does not improve the maximum turbine efficiency. In addition, as a result of these experiments, it was determined that for a 24 deg angle of attack 0.68 was the most efficient inner-to-outer diameter ratio, whereas for higher angles of attack the maximum efficiency decreases with an increase in the diameter ratio from 0.60 to 0.75.

Svrha ovoga rada je da se konstruira prototip crossflow turbine kojoj je rotor širine 100 mm u svrhu ispitivanja. Rad opisuje postupak konstrukcije crossflow turbine kao i sve pojmove uz to. Rad se sastoji od tri dijela koji su međusobno povezani. Prvi dio rada obuhvaća programske pakete koji su korišteni u konstrukciji i vizualizaciji modela. Opisuje vrste, važnost kao u njihovu uporabu kroz povijest računalne 3D konstrukcije Drugi dio rada bazira se na pojmu hidroelektrana. Opisuju se vrste hidroelektrana, princip rada, tehničke specifikacije i primjena različitih hidroelektrana. U trećem dijelu objašnjava se pojam cossflow turbine, naćin rada kao i primjena iste. Opisuje se svaka komponenta turbine i radi se proračun vratila i ležajeva.

The total installed capacity of the hydropower stations in Pakistan is about 7,000 MW which is about 20% of the total available hydro power potential. For possible micro-hydro stations, a potential of about 1300 MW exists at a number of low head and high flow rate sites. Work has been reported by Chattha et al. [1, 2] related to installation of a micro-hydro power station at one of the typical sites. An axial flow pump-as-turbine (PaT) was installed to generate electrical power at the micro-hydro station. The site selected for this work is quite typical and efforts are now being made to utilize the maximum potential of the site conditions. The PaT only utilizes about half of the available flow of water and a spillway was constructed at this site to divert the excess amount of water. The diverted water flows back to the main stream after bypassing the PaT. Work is now being carried out to explore the installation of a turbine in the spillway to harness the energy potential of the diverted water stream. This work includes selection, design, fabrication and installation of a turbine in order to generate electrical power utilizing the energy of water diverted to the spillway. A 100 ft3/sec flow rate with about 11 ft head is available at the spillway side. Considering these site conditions and indigenous fabrication expertise, cross flow type turbine has been selected for installation. Cross flow turbines are being manufactured in Pakistan and are usually quite successful for micro-hydro systems. Based on the available site conditions, a cross flow turbine has been designed. The diameter and length of the turbine runner have been calculated. Furthermore, the number of blades and radius of curvature have been determined along with other design parameters. The designed turbine is expected to produce about 50 kW of power. The complete design of the turbine, based on the available site conditions is presented in this paper.

Cross Flow Turbines (CFT), also known as Banki or Ossberger turbines are broadly used in small scale hydropower generation. Easy construction and operation, low CAPEX and OPEX and fairly independent efficiency from flow rate are the main characteristics of the CFT. However, they also tend to have a modest efficiency (80%), hence they are not considered for large scale power plants. Previous work have focused on use of Internal Deflectors (ID) for CFT efficiency improvement. However experimental flow observation and characterization inside CFT is hard to achieve. This work proposes use of Computational Fluid Dynamic (CFD) tools as an aid in ID design. A transient regime, two-dimensional, numerical model of a CFT without any internal deflectors was carried out. Deviation from experimental results at BEP was close to 5%. CFT w/o ID results were used as ID design starting point. Parameters: Upper Blade Position and ID Length were defined and varied obtaining six different ID versions. Numerical models were carried out for evaluation of ID effect on CFT. CFT hydraulic efficiency improvement was achieved for all ID versions studied (range 0.5%–3%, average:1.9%). Output power was also augmented (range 0.3%–4%, average:2.5%)for all cases.Copyright © 2012 by ASME

This study attempts to identify the contribution of the two stages of power generation to the shaft power in a cross‐flow turbine. A special model of the turbine is built to allow insertion of a flow diverter inside the runner. A flow diverter is also designed to intercept the flow that passes through the first stage of the turbine. Tests are conducted with and without the diverter to determine the contribution of the two stages of the turbine to shaft output. Measurements are taken to ensure that presence of the flow diverter does not cause back pressure inside the nozzle. Contribution of the first stage to output is determined from tests with the diverter installed. Total shaft power is determined by removing the diverter. The balance between the two is the contribution of the second stage. The turbine's second stage contributes more significantly to the shaft output than reported in the analytic literature. Turbine efficiency can be improved if efforts are concentrated on improving the performance of t...

Pico hydro generators a promising means of providing costare -effective electricity to locations with limited or no availability of grid-supplied electricity. The Firefly design has been employed throughout rural areas of Cameroon and as a light battery charger. It is hoped to extend the turbine capacity to used providesteady baseload output between 100-500 W operating at low head sites (2-10 m). Suitability of the Firefly under these conditions is currently unknown, and the turbine has not been evaluated under conditions of very low head. The study objective was to characterize the performance through laboratory testing under conditions of low head and variable flow rate, in order to determine if the Firefly turbine meets the requirements of users in Cameroon. At this time, construction has been completed of the Firefly turbine and testing apparatus. The testing process and initial Firefly performance results, as well as lessons learned to date, arethe focus of this paper. This is the first phase of a larger project seeking to design an optimized pico hydro turbine that balances performance, reliability and ease of manufacture and installation. The Firefly results will be used as a baseline in comparisons to new turbine designs.

A number of numerical methods have been developed to predict the performance and aerodynamic loads of the Darrieus turbine. Prior work by Reference [1] using blade element methods (BEM) and free vortex methods (FVM) [2] has produced reasonable models that predict the hydrodynamic performance of the Darrieus turbine. The validated models reasonably estimate the performance at low solidities (Nc/R≪1), but lose accuracy at higher solidity ratios. Dynamic stall and flow curvature has been recognized by [2] [3] and [4] to be significant modeling parameters which have limited the accuracy of prior models. The current numerical model extends the predictions of the FVM model to a higher solidity ratio range. An improved model is presented for the condition of high angles of attack and for dynamic stall,. Experimental data on a series of two (Nc/R≈.9) and four (Nc/R≈1.8) blade configurations are presented as validation of the modified analytical vortex model.

The aim of this study is to develop a nano-hydraulic turbine which can be generated by the flow at drop structure in irrigation channels or industrial waterways. This study has focused on an open type cross-flow turbine without any attached equipment for minimizing production, installation and maintenance cost. The water flow condition towards the runner is one of the important factors of stable supply of electricity. This study was used a curved channel which consists of a curved part and a straight part as changing the flow direction. When water is flowed this channel, free surface of the water flow has a distinctive shape, standing wave. The high amplitude of the standing wave makes the runner efficiency lower. The objective of this study is to suppress the fluctuation of the water surface when the curved channel control is presented by changing the setting angle of straight part of the channel. The behavior of the water surface, the fluctuation pattern, and the velocity of the water flow are critical to the runner performance. By variation of the channel angle, both parameters were compared and evaluated.

This study attempts to investigate the performance and internal flow characteristics of a cross-flow turbine by guide vane angle. In order to improve the performance of a cross flow turbine, the paper presents a numerical investigation of the turbine with air supply and discusses the influence of variable guide vane angle on the internal flow. A newly developed air supply from air suction Hole is adopted. To investigate the performance and internal flow of the cross-flow turbine, the CFD software based on the two-phase flow model is utilized. The numerical grids are made in two-dimensional geometry in order to shorten the time of two-phase calculations. Then a series of CFD analysis has been conducted in the range of different guide vane angle. Moreover, local output power is divided at different stages and the effect of air layer in each stage is examined.

The aim of this investigation is to develop an open type cross-flow turbine for environmental friendly nano-hydraulic turbine utilizing extra-low head waterfall. A relative position between the runner and the waterfall is one of the important factors for turbine efficiency. More often, it is necessary to precisely adjust this distance according to changes of the flow rate. In this study, we focused on the influence of the horizontal and vertical position of the runner on performance. First, the effect on the performance of the horizontal relative position between the runner and the falling water is verified. Next, two condition of the vertical relative position are concerned; one is the clearance between the runner and the water surface of the pool, the other is that between the runner and the solid surface as the runner placed closer to the ground or the riverbed. The result highlights that the horizontal relative position was an effect on the power performance. When the solid surface is presented under the runner, the performance is not effected when the water thickness is equivalent to 7.5% or more. On the other hand, when water surface is presented below the runner, the clearance between them has insignificant effect on the performance even though the runner underside is partly submerged.

This study presents a numerical investigation of a generic horizontal axis cross-flow marine turbine. The numerical tool used is the commercial Computational Fluid Dynamics package ANSYS FLUENT 12.0. The numerical model, using the SST k-w turbulence model, is validated against static, dynamic pitching blade and rotating turbine data. The work embodies two main investigations. The first is concerned with the influence of turbine solidity (ratio of net blade chord to circumference) on turbine performance, and the second with the influence of blockage (ratio of device frontal area to channel crosssection area) and free surface deformation on the hydrodynamics of energy extraction in a constrained channel.Turbine solidity was investigated by simulating flows through two-, three- and four-bladed turbines, resulting in solidities of 0.019, 0.029 and 0.038, respectively. The investigation was conducted for two Reynolds numbers, Re = O(10^5) & O(10^6), to reflect laboratory and field scales. Increasing the number of blades from two to four led to an increase in the maximum power coefficient from 0.43 to 0.53 for the lower Re and from 0.49 to 0.56 for the higher Re computations. Furthermore, the power curve was found to shift to a lower range of tip speed ratios when increasing solidity.The effects of flow confinement and free surface deformation were investigated by simulating flows through a three-bladed turbine with solidity 0.125 at Re = O(10^6) for channels that resulted in cross-stream blockages of 12.5% to 50%. Increasing the blockage led to a substantial increase in the power and basin efficiency; when approximating the free surface as a rigid lid, the highest power coefficient and basin efficiency computed were 1.18 and 0.54, respectively. Comparisons between the corresponding rigid lid and free surface simulations, where Froude number, Fr = 0.082, rendered similar results at the lower blockages, but at the highest blockage an increase in power and basin efficiency of up to 7% for the free surface simulations over that achieved with a rigid lid boundary condition. For the free surface simulations with Fr = 0.082, the energy extraction resulted in a drop in water depth of up to 0.7%. An increase in Fr from 0.082 to 0.131 resulted in an increase maximum power of 3%, but a drop in basin efficiency of 21%.