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In this study, the computational and experimental examination of the hydraulic cross-flow turbine (CFT) is presented. The experimental studies are conducted at the turbine laboratory of Gebze Technical University. The commercial Computational Fluid Dynamics (CFD) software, Star CCM+, is employed to calculate three-dimensional, incompressible, steady Reynolds-Averaged Navier–Stokes (RANS) equations for the flow inside the CFT. In the numerical model, the rotational motion of the blades is modeled by means of the moving reference frame approach. The correlation between the turbulent viscosity and the velocities is acquired using the standard k-ɛ turbulence model. The computational results are obtained in terms of the torque, power, and efficiency of the turbine. The outcome of this research reveals that the CFD software used in this study can reliably be used to predict experiments since the numerical model can accurately estimate the experimental values of the torque, power, and efficiency of the CFT. [ABSTRACT FROM AUTHOR]

Cross-flow turbines convert kinetic power in wind or water currents to mechanical power. Unlike axial-flow turbines, the influence of geometric parameters on turbine performance is not well-understood, in part because there are neither generalized analytical formulations nor inexpensive, accurate numerical models that describe their fluid dynamics. Here, we experimentally investigate the effect of aspect ratio—the ratio of the blade span to rotor diameter—on the performance of a straight-bladed cross-flow turbine in a water channel. To isolate the effect of aspect ratio, all other non-dimensional parameters are held constant, including the relative confinement, Froude number, and Reynolds number. The coefficient of performance is found to be invariant for the range of aspect ratios tested (0.95–1.63), which we ascribe to minimal blade–support interactions for this turbine design. Finally, a subset of experiments is repeated without controlling for the Froude number, and the coefficient of performance is found to increase, a consequence of the Froude number variation that could mistakenly be ascribed to aspect ratio. This highlights the importance of a rigorous experimental design when exploring the effect of geometric parameters on cross-flow turbine performance. [ABSTRACT FROM AUTHOR]

Continuous and reliable power supply plays an important role for water leakage monitoring systems used in urban water supply pipes. Renewable energies powered water leakage monitoring system is becoming a promising way to reduce the dependence on traditional chemical batteries. In this study, an inline vertical cross-flow turbine was developed to harvest the potential hydropower inside water supply pipes for supplying power to the water monitoring systems. Specifically, numerical investigations are carried out on the block shapes of a water turbine system to determine an optimal model. The effects of tip clearance on the turbine performance are conducted and it is found that a smaller tip clearance can reduce the reversing torque on the returning blades and increase the pressure drop through the runner for improving the turbine performance. Besides, a self-adjustable vane is designed to avoid excess water head loss. The simulation results show that the proposed self-adjustable vane is effective to limit the water head loss at high flow velocities (1.5–2.0 m/s) to 5 m. Finally, the turbine prototype is fabricated and tested on a lab test rig. The experimental results indicate that the numerical method adopted in this research is accurate enough for such micro water turbine performance prediction. A month-long test shows that the daily electricity generation of the proposed turbine is about 600 Wh and the water head loss is always below 5 m, which means that the proposed turbine can provide sufficient power for any general water leakage monitoring system without influencing normal water supply. [ABSTRACT FROM AUTHOR]

The inline cross-flow turbine is a promising and reliable device to harvest hydropower in an urban water supply pipeline for power supply to its water supply monitoring system. However, investigations about the influencing factors on the performance of inline cross-flow turbines are still rare and this paper focuses on the effect of their runner inlet arc angle for improving the device's performance. Firstly, a mathematical design method for the turbine's blocks is developed. With the proposed method, four models with different runner inlet arc angles are developed. The turbine's performance, function of conversion block, flow velocity characteristics, pressure distribution and blades torque output of the models are then analyzed. Results indicate that a smaller runner inlet arc can increase the flow velocity at runner inlet and pressure difference between the upstream and downstream of the runner, resulting in a higher output power but also a higher overall water head reduction through the turbine. Besides, it is found that the runner inlet arc angle has a significant influence on the power output of runner second stage. With the increase of runner inlet arc angle, the torque output at the second stage encounters a gradual decrease. To achieve a good balance between turbine efficiency and water head reduction, the suggested runner inlet arc angle is 105°. Numerical results showed that the model with 105° runner inlet arc angle could produce a maximum power generation efficiency of 42.6% with about 1.6 kW power output. [ABSTRACT FROM AUTHOR]

Recent experimental studies suggest that the usual way of measuring and predicting the efficiency of the cross-flow turbine do not describe the flow physics adequately. This verification led to the present investigation of some of the more relevant aspects related to the efficiency of this type of turbine. After presenting a detailed description of the rig used in the tests, the most adequate way of measuring the efficiency is discussed, including the specification of the proper datum used for the measurement of the head. Typical curves for the measured efficiency are shown, demonstrating that a peak efficiency of 84.8% is attainable with the cross-flow turbine, using new geometric relations, markedly different from those proposed by the present know-how in this field. Analysis of the experimental data seems to suggest that one of the reasons for the detected discrepancies is the assumption for the direction of the flow leaving the rotor. The consequences of the new physical insight are explored in this paper, leading to new theoretical relations for the efficiency evolution. It is demonstrated that the new theory describes reality better than previous analysis by comparing some of its predictions with experimental data. [ABSTRACT FROM AUTHOR]

Abstract: The potential energy hidden in water resources is becoming more and more a significant economic value. The value of the hydroelectric energy is often magnified by the proximity of the turbine to pumps or other energy sinks owned by the same water manager. Cross-flow or Banki-Michel turbines are a very efficient and economic choice that allows a very good cost/benefit ratio for energy production located at the end of conduits carrying water from a water source to a tank. In the paper the optimum design of a cross-flow turbine is sought after, assuming a flow rate variable in time. Regulation of the discharge entering in the turbine is a key issue, which is faced adopting a shaped semicircular segment, moved inside the main case around the rotating impeller. The maximum efficiency of the turbine is attained by setting the velocity of the particles entering the impeller at about twice the velocity of the rotating system at the impeller inlet. If energy losses along the pipe are negligible, closing and opening the inlet surface with the semicircular segment allows always a constant hydraulic head and a constant velocity at the impeller inlet, even with different flow rate entering values. Observed reduction of the turbine efficiency along with the inlet surface reduction is first investigated; a design methodology, using also CFD simulations, is then proposed; finally, the same methodology is applied to a real site in Sicily, selected in the context of the HYDROENERGY P.O. - F.E.S.R. European project. [Copyright &y& Elsevier]

When experimentally evaluating the performance of a wind or water current turbine, one must impose a regulating torque on the turbine rotor by electrical or mechanical means. Some options limit this controlling torque to a purely resistive quantity, while servomotors and stepper motors allow torque to be applied in the direction of turbine rotation. Any control mode that results in net positive power for a turbine may be of interest for energy harvesting, and all of these are net "fluid-driven." Here, we present experiments that characterize the power, torque, and force coefficients of a cross-flow turbine operated at a constant rotational speed or under a constant imposed control torque. Time- and phase-average performance coefficients are largely equivalent for the two strategies although torque-regulated control is restricted to a narrower range of rotational speeds and the two strategies result in slightly different blade kinematics. [ABSTRACT FROM AUTHOR]

An important component of the management cost of aqueducts is the energy costs. Part of these costs can be recovered by transforming some of the many existing energy dissipations into electric energy by means of economical turbines. This paper describes an experimental study that has been carried out in order to (1) test the performance of an economical cross-flow turbine that maintains high efficiency within a large range of water discharges, and (2) validate a new approximate formula relating main inlet velocity to inlet pressure. It is demonstrated that the proposed formula, on the basis of some simplifying assumptions, exactly links inlet velocity to inlet pressure with any possible geometry of the cross-flow turbine. A specific facility was designed and constructed inside the hydraulic laboratory of the Dipartimento di Ingegneria Civile, Ambientale, Aerospaziale dei Materiali (DICAM) Department of the University of Palermo to carry out the experiments. Both numerical and experimental tests were carried out for the two cases of turbine impeller with and without the internal shaft. Experimental and numerical results showed a good agreement and give an excellent validation of the proposed formula, which can be readily used for a fast and reliable design of a cross-flow turbine. [ABSTRACT FROM AUTHOR]

• Small hydrokinetic turbine that obtains energy from low velocity water streams. • The current blockage is a key factor on the turbine performance. • Cross-flow simple design based on commercial components coupled on a vertical axis. • Tested experimentally on a Hydrodynamic Water. • Experimental results were complemented by simulations of a CFD numerical model. Obtaining electrical energy from water streams with velocities below one meter per second using hydrokinetic turbines presents an important challenge as it is significantly lower than the range of operations (higher than two meters per second) offered by units currently commercialized. This research goes one step further than the state-of-the-art studies regarding the degree to which energy extraction is influenced by the water flow blockage caused by turbines in water flows; presenting that blockage as a key factor in the procurement of electrical energy using hydrokinetic micro turbines from low-velocity flowing water. Primarily, it describes the design and characterization of a small vertical-axis cross-flow hydrokinetic turbine whose dimensions maximize the blockage of the water circulating in a channel at very low velocity. For the turbine characterization, a model has been tested experimentally in a water tunnel with different flow rates and complemented by simulations under the same conditions using an adjusted computational fluid dynamics model. The experimental tests contemplate the measuring of the turbine's electrical power, hydraulic coefficient and rotational speeds. The simulations of the numerical model facilitate the procurement of the corresponding water pressure and velocity fields. Further analysis has allowed for a closer examination of the different type of forces exerted on the faces of the blades as well as their position. Upon even closer inspection there appear to be a variety of possible scenarios contingent on the turbine load. [ABSTRACT FROM AUTHOR]

The cross-flow turbines cover from the point of view hydraulic power the running domain of some well-known turbines such as Pelton, Francis or Kaplan. This type of turbine has a simple construction, long life and low execution cost, which makes it very suitable for on and off grid small to medium hydro power plants. It is quite difficult to establish an exact theoretical dynamic model for this type of turbines, due to the complex flow phenomenon (bi phase flow water and air). In order to obtain the exact dynamic behavior of the hydraulic machine, experimental dynamic identification will be done. In automation, the dynamic properties, represent the fundamental characteristic of the object which must be regulated. When the dynamic properties of the regulated object are obtained experimentally, we analyze the characteristics of the transient regime, which appears because of the application at the system inlet of some stochastic or deterministic signals (sine waves for our case). The hydraulic turbine is modeled as an informational quadrupole having the inlet parameters the movement of the wicket gate and the turbine head and outlet parameters the torque and the speed. In this paper it will be presented the frequency modelling of the cross-flow turbine and the validation of the mathematical model through experimental dynamic identification. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In order to study the internal flow state and wear law of a bulb cross-flow unit based on the particle non-uniform phase model in the Euler–Euler method, the solid-liquid two-phase flow condition of the hydraulic turbine under different solid-phase diameters, concentrations, and guide vane openings is calculated. The results show that (1) Under the same solid-phase physical parameters, the distribution of solid-phase concentration on the working surface of the blade is positively correlated with the opening degree of the guide vane, the concentration of the solid phase on the back of the blade is negatively correlated with the opening degree of the guide vane. (2) The addition of the solid phase changes the time-domain period of pressure pulsations at the rotor inlet and the tailpipe inlet under clear water conditions, and the tailpipe pressure pulsation coefficient decreases with increasing solid-phase concentration. The pressure pulsation coefficient increases with increasing solid-phase diameter and concentration at the inlet of the rotor. (3) Numerical simulation of the wear characteristics of cross-flow turbine by Finne's wear model reveals that the two-phase flow condition with high concentration, large particle size and small openings has a more serious effect on turbine blade wear. [ABSTRACT FROM AUTHOR]

Cross-flow turbines have recently been proposed for energy recovery in aqueducts when the outlet pressure is greater than zero, owing to their constructive simplicity and good efficiency within a large range of flow rates and head drops. In the case of high head drop (higher than 150 m) and relatively small discharge (lower than 0.2 m3/s), the traditional design of these turbines leads to very small widths of the nozzle and the runner; as a consequence, friction losses grow dramatically and efficiency drops down to very low values. Standard Pelton turbines require zero outlet pressure and cannot be used as alternatives. A new counter-pressure hydraulic turbine for high head and low flow rate, called the High Power Recovery System (H-PRS) is proposed. H-PRS presents a different geometry to reduce friction losses inside the nozzle and the runner by widening the two external walls. Several curved baffles are proposed to guide the fluid particles inside the nozzle and to guarantee the right velocity direction at the inlet surface of the runner. Computational Fluid Dynamics (CFD) 3D transient analyses are carried out to measure H-PRS efficiency for different operating conditions and to compute its characteristic curve for different positions of the regulating flap. [ABSTRACT FROM AUTHOR]

This paper introduces a new methodology for designing and optimizing the performance of hydraulic Cross-Flow turbines for a wide range of operating conditions. The methodology is based on a one-step approach for the system-level design phase and a three-step, successive numerical analysis approach for the detail design phase. Compared to current design methodologies, not only does this approach break down the process into well-defined steps and simplify it, but it also has the advantage that once numerical simulations are conducted for a single turbine, most of the results can be used for an entire class of Cross-Flow turbines. In this paper, after a discussion of the research background, we explain the design process used and the ANSYS®-based CFD model of the turbine in detail. The design process consists of three steps. First, designing nozzle geometry; second, optimizing runner parameters; and third, enhancing turbine performance by analyzing various load conditions. A turbine designed using this process in a simulation case study achieves a peak hydraulic efficiency of 91% and peak overall efficiency of 82% that is maintained for volume flow rates as low as 14% of the nominal value and water head variations up to 30% of the nominal value. • A novel design methodology for hydraulic Cross-Flow turbines is proposed. • The two-dimensional steady state simulations were performed in ANSYS CFX. • Numerical results were validated with experimental data. • The proposed design methodology was used in a case study to design a new turbine. • The designed turbine maintains above 80% efficiency for a range of load conditions. [ABSTRACT FROM AUTHOR]

In laboratory experiments involving wind or water turbines, it is often desirable to correct measured performance for the effects of model blockage. However, there has been limited experimental validation of the analytical blockage corrections presented in the literature. Therefore, the objective of this study is to evaluate corrections against experimental data and recommend one or more for future use. For this investigation, we tested a cross-flow turbine and an axial-flow turbine under conditions of varying blockage with other non-dimensional parameters, such as the free-stream Reynolds and Froude numbers, held approximately constant. Increasing blockage improved turbine performance, resulting in higher thrust and power coefficients over a larger range of tip-speed ratios. We used these experimental data to assess the effectiveness of multiple analytical blockage corrections for both turbine types. Of the corrections evaluated, the two based on measured thrust performed best. These corrections were more effective for the cross-flow turbine than the axial-flow turbine. We attribute this result to changes in the local Reynolds number caused by increasing blockage, an effect not captured by the analytical theory. For both turbines, the corrections performed better for thrust than power, which is consistent with the assumptions that underlie the analytical theory. • Flow confinement augments the performance of wind and water turbines. • Analytical blockage corrections account for some of the effects of flow confinement. • Thrust-based corrections perform best and are recommended for future use. • Reynolds dependence may impact the effectiveness of blockage corrections. • Assumptions that underpin momentum theory introduce some error into corrections. [ABSTRACT FROM AUTHOR]

Undershot cross-flow water turbines are characterized by their being easily applicable to open channels with various widths and depths by changing their blade width and/or the outer diameter of the runner. On the other hand, as this water turbine operates in a free-surface flow field, it is expected that when the flow rate changes, the flow field around the runner including the water depth changes dramatically, and that the turbine performance also changes. Thus, the objective of this study is to elucidate the effect of flow rate on the performance and flow field of an undershot cross-flow water turbine. By changing the flow rate, we conduct experiments and free surface flow analysis on the water turbine, as well as torque component analysis. The result showed that, among the torques in the respective flow regions, that torque resulting from the second stage cross-flow was dominant. Furthermore, it was found that among the respective dynamic components of the torque, the most dominant component was the gravitational component for low flow rates and the angular momentum component for medium-to-high flow rates. We expect these results to contribute to the establishment of higher performance design guidelines, such as optimum shapes for the flow rates. • The undershot cross-flow water turbine is applicable to open channels of various widths and depths. • The effect of flow rate on the performance of the present water turbine were elucidated. • The flow field was elucidated at different flow rates. • The breakdown of the torque into its flow rons and dynamic components were elucidated. [ABSTRACT FROM AUTHOR]

Hydraulic turbines for energy recovery in wastewater treatment plants, with relatively large discharges values and small head jumps, are usually screw Archimedes or Kaplan types. In the specific case of a small head jump (about 3 m) underlying a rectangular weir in the major Palermo (Italy) water treatment plant, a traditional Kaplan solution is compared with two other new proposals: a Hydrostatic Pressure Machine (HPM) located at the upstream channel and a cross-flow turbine (CFT) located in a specific underground room downstream of the same channel. The fluid mechanical formulations of the flow through these turbines are analyzed and the characteristic parameters are stated. Numerical analysis was carried out for the validation of the HPM design criteria. The efficiency at the design point of the CFT and HPM are estimated using the ANSYS CFX solver for resolution of 3D URANS analysis. The strong and weak points of the three devices are compared. Finally, a viability analysis is developed based on several economic indicators. This innovative study with a theoretical formulation of the most suitable turbomachine characterization, the potential energy estimation based on hydraulic energy recovery in a real case study of a wastewater treatment plant and the comparison of the three different low-head turbines, enhancing the main advantages, is of utmost importance towards the net-zero water sector decarbonization. [ABSTRACT FROM AUTHOR]

Abstract: This paper is the second of three, which outline the procedures and results for a set of experiments on various configurations of the Transverse Horizontal Axis Water Turbine (THAWT), which is a horizontally orientated variant of the Darrieus cross-flow turbine. Tests were conducted in the combined wind, wave and current tank at Newcastle University on a 0.5 m diameter rotor, while the flow depth and velocity were varied over a range of realistic Froude numbers for tidal streams. Various configurations of the device were tested to assess the merits of varied blade pitch, rotor solidity, blockage ratio and truss oriented blades. Experiments were carried out using a speed controlled motor/generator, allowing quasi-steady results to be taken over a range of tip speed ratios. Measurements of power, thrust, blade loading and free surface deformation provide extensive data for future validation of numerical codes and demonstrate the ability of the device to exceed the Lanchester–Betz limit for kinetic efficiency, by exploiting high blockage. This second paper covers the instrumentation and analysis for the structural loading for the parallel bladed variant of the THAWT device. The first paper covers the experimental setup and hydrodynamic performance of the parallel bladed rotor, and the third paper covers both performance and loading of the truss configured THAWT device. [Copyright &y& Elsevier]

Abstract: This paper is the third of three, which describe the procedures and results for a set of experiments on various configurations of the Transverse Horizontal Axis Water Turbine (THAWT), which is a horizontally orientated variant of the Darrieus cross-flow turbine. Tests were conducted in the combined wind, wave and current tank at Newcastle University on a 0.5 m diameter rotor, while the flow depth and velocity were varied over a range of realistic Froude numbers for tidal streams. Various configurations of the device were tested to assess the merits of varied blade pitch, rotor solidity, blockage ratio and truss oriented blades. Experiments were carried out using a speed-controlled motor/generator, allowing quasi-steady results to be taken over a range of tip speed ratios. Measurements of power, thrust, blade loading and free surface deformation provide extensive data for future validation of numerical codes and demonstrate the ability of the device to exceed the Lanchester–Betz limit for kinetic efficiency by using high blockage. This paper covers the instrumentation, hydrodynamic performance and loading of the truss bladed variant of the THAWT device. The first paper covers the experimental setup and hydrodynamic performance of the parallel bladed rotor and the second paper covers the instrumentation and hydrodynamic loading of the parallel bladed rotor. [Copyright &y& Elsevier]

Abstract: This paper is the first of three, which outline the procedures and results for a set of experiments carried out on various configurations of the Transverse Horizontal Axis Water Turbine (THAWT), which is a horizontally orientated variant of the Darrieus cross-flow turbine. Tests were conducted in the combined wind, wave and current tank at Newcastle University on a 0.5 m diameter rotor, while the flow depth and velocity were varied over a range of realistic Froude numbers for tidal streams. Various configurations of the device were tested to assess the merits of varied blade pitch, rotor solidity, blockage ratio and truss oriented blades. Experiments were carried out using a speed controlled motor/generator, allowing quasi-steady results to be taken over a range of tip speed ratios. Measurements of power, thrust, blade loading and free surface deformation provide extensive data for future validation of numerical codes and demonstrate the ability of the device to exceed the Lanchester-Betz limit for kinetic efficiency by using high blockage. This paper covers the experimental procedures and results for the hydrodynamic performance for the parallel bladed variant of the THAWT device. The second paper covers the hydrodynamic loading of the parallel bladed rotor and the third covers both hydrodynamic performance and loading of the truss configured THAWT device. [Copyright &y& Elsevier]

This study developed a microhydraulic turbine that can stably and efficiently generate electricity even in canals where snow and ice masses frequently flow down. An undershot cross-flow hydraulic turbine was selected as the development target, and experiments were conducted in an irrigation canal in a heavy snowfall area. Spherical snowballs were made to flow down to the turbine from the upstream direction. The behavior of the snowballs and the power generation performance were investigated as these snowballs passed through the rotor. When the diameter of the snowball is smaller than the blade interval of the rotor, the snowball passing through the rotor causes a small decrease in power output. In contrast, when the diameter of the snowball is larger than the blade interval, the snowball is entrained between the rotor and canal bottom, temporarily stopping the rotor, and resulting in a large decrease in power generation. These results suggest that an undershot cross-flow hydraulic turbine can reduce power generation performance due to snow and ice masses when its blade interval is larger than the expected size of the snow and ice masses. This study developed some design guidelines for this turbine that are highly adaptable to snow- and ice-flowing irrigation canals. • This study is concerned with a undershoot cross-flow turbine in snow areas. • Behavior of snowballs passing through the rotor is successfully explored. • Power output decreases slightly when the snowball passes through the rotor. • Large snowball temporarily stops the rotor and greatly decreases the power output. • Design guidelines for the undershoot cross-flow turbine in snow areas are presented. [ABSTRACT FROM AUTHOR]

The flow and torque mechanisms of an open cross-flow hydraulic turbine in an underflow operation are investigated through experiments and numerical simulations. The unsteady flow field around a hydraulic turbine is measured in an open-circuit water tunnel using phase-averaged particle image velocimetry, and the results are compared with those of a two-dimensional numerical simulation using the volume of fluid method for two-phase flow analysis. The experimental and numerical results of the flow field agree well with each other, suggesting the validity of the two-dimensional numerical simulation for open cross-flow hydraulic turbines. The experimental and numerical results indicate that both the accelerated flows over the downstream blade and through the bottom spacing between the turbine and channel wall yielded the positive torque generation of the cross-flow turbine. The former effect is caused by the stagnation pressure on the concave side of the blade and the formation of accelerated flow on the convex side of the blade, both of which are observed at a low tip-speed ratio. The latter effect of bottom spacing is caused by the converging flow effect of the local velocity between the lower side of the turbine and the channel wall. It is discovered that these flow features improved by decreasing the bottom spacing, and that they contributed to the local torque generation; consequently, the torque performance and efficiency of the cross-flow turbine improved. However, very small bottom spacing may not be effective for improving the efficiency. • The flow field of open-cross-flow hydraulic turbine was measured by phase-averaged particle image velocimetry. • The measured flow field was well reproduced by numerical simulation using volume of fluid method. • The flow field was featured by the accelerated flows through the blade passages and that in the bottom spacing. • The accelerated flows contribute to the torque mechanism of open-cross-flow hydraulic turbine. • The efficiency of cross-flow hydraulic turbine was improved at small bottom spacing. [ABSTRACT FROM AUTHOR]

Exploitation of small hydropower sources requires the use of small turbines that combine efficiency and economy which can conveniently cater the power needs of rural and small communities. Cross-flow turbines are used widely in such micro hydropower plants due to their simple design, easier maintenance, low initial investment and modest efficiency. Also, because of their suitability under low heads, their efficient operation under a wide range of flow variations and ease of fabrication, cross-flow turbines have been extensively employed. The primary objective of this study is to numerically analyze the characteristics and the fluid flow in a cross-flow hydro turbine and to optimize its performance by geometrically modifying the several parameters. During the process, a base model was chosen, the design was modified simultaneously by varying the nozzle shape, changing the guide vane angle, varying the number of runner blades and simulations were carried out individually. Two phase (air & water at 25 °C), steady state with SST turbulence model was selected in the commercial CFD code ANSYS CFX 13.0 for the numerical simulation. The design parameters included 10 m head, 0.1 m 3 /s flow rate and 642 rpm rotational speed. The results obtained showed that the best efficiency obtained from the base nozzle was 63.67% which was geometrically modified that improved the turbine performance and the efficiency reached 76.60% (increase by 12.93%). Velocity distribution, pressure contours, output torque within the flow domain were also characterized. It was observed that the re-circulating flow region was reduced and also its pattern was varied. [ABSTRACT FROM AUTHOR]

In the context of energy shortages and the development of new energy sources, tidal current energy has emerged as a promising alternative. It is typically harnessed by deploying arrays of multiple water turbines offshore. Vertical axis water turbines (VAWTs), as key units in these arrays, have wake effects that influence array spacing and energy efficiency. However, existing studies on wake velocity distribution models for VAWTs are limited in number, accuracy, and consideration of influencing factors. A precise theoretical model (Lam's formula) for wake lateral velocity can better predict wake decay, aiding in the optimization of tidal current energy array designs. Turbulence in the ocean, serving as a medium for energy exchange between high-energy and low-energy water flows, significantly impacts the wake recovery of water turbines. To simplify the problem, this study uses software ANSYS Fluent 2020 R2 for two-dimensional simulations of VAWT wake decay under different turbulence intensities, confirming the critical role of turbulence intensity in wake velocity decay. Based on the obtained data, a new mathematical approach was employed to incorporate turbulence intensity into Lam's wake formula for VAWTs, improving its predictive accuracy with a minimum error of 1%, and refining some parameter calculations. The results show that this model effectively reflects the impact of turbulence on VAWT wake recovery and can be used to predict wake decay under various turbulence conditions, providing a theoretical basis for VAWT design, optimization, and array layout. [ABSTRACT FROM AUTHOR]

This study focused on the development of an undershot open cross-flow turbine that is applicable in extremely low head hydropower conditions, especially in rapid and shallow streams such as agricultural waterways in mountain areas. A model of the cross-flow turbine was constructed and examined experimentally. The authors evaluated the effect of the flow conditions on undershot wheel power performance. The effect of the number of blades and the blade thickness on runner performance was also investigated. It was found that the power coefficient changed drastically with varying impinging flow thickness and runner installation height. Power could be generated when the impinging flow thickness was less than 28% of the runner diameter. The maximum power coefficient, CPmax, increased as the impinging flow thickness was decreased. Furthermore, a higher CPmax was obtained as the runner installation height was lowered. This was because the water flow was inclined between the runner and the bottom wall of the channel. In this study, the highest CPmax obtained was 0.401. [ABSTRACT FROM AUTHOR]

A cross-flow air turbine, which is a self-rectifying, air-driven turbine, was designed and proposed for the power take-off (PTO) system of an oscillating water column (OWC) wave energy converter (WEC). To predict the complicated non-linear behavior of the air turbine in the OWC, numerical and experimental investigations were accomplished. The geometries of the nozzle and the rotor of the turbine were optimized under steady-flow conditions, and the performance analysis of the model in bi-directional flows was conducted by commercial computational fluid dynamics (CFD) code ANSYS CFX. Experimentation on the full-scale turbine was then undertaken in a cylindrical-type wave simulator that generated reciprocating air flows, to validate the numerical model. The optimized model had a peak cycle-averaged efficiency of 0.611, which is 1.7% larger than that of the reference model, and a significantly improved band width with an increase in flow coefficients. Under reciprocating-flow conditions, the optimized model had a more improved operating range with high efficiency compared to the performance derived from the steady-flow analysis, but the peak cycle-averaged efficiency was decreased by 4.3%. The numerical model was well matched to the experimental results with an averaged difference of 3.5%. The proposed optimal design having structural simplicity with high performance can be a good option to efficiently generate electricity. [ABSTRACT FROM AUTHOR]

Hydraulic turbines have become indispensable for harnessing renewable energy sources, particularly in-pipe hydraulic turbine technology, which leverages excess energy within pipeline systems like drinking water distribution pipes to produce electrical power. Among these turbines, the propeller-type axial turbine with circular blades stands out for its efficiency. However, there is a notable lack of literature on fluid dynamics and structural behavior under various operational conditions. This study introduces a comprehensive methodology to numerically investigate the hydraulic and structural responses of turbines designed for in-pipe installation. The methodology encompasses the design of circular blades, followed by parametric studies on fluid dynamics and structural analysis. The circular blade's performance was evaluated across different materials, incorporating static, modal, and harmonic response analyses. Results showed that the circular blade achieved a peak hydraulic efficiency of 75.5% at a flow rate of 10 l/s, generating 1.86 m of head pressure drop and 138 W of mechanical power. Structurally, it demonstrated a safety factor exceeding 1 across the entire hydraulic range without encountering resonance or fatigue issues. This research and its methodology significantly contribute to advancing the understanding of designing and assessing the fluid dynamic behavior and structural integrity of circular blades in axial propeller-type turbines for in-pipe installations, serving as a valuable resource for future studies in similar domains. [ABSTRACT FROM AUTHOR]

The development of new hydro turbines or the optimization of traditional hydro turbines is one of the research directions that scholars have been interested in to broaden the source of hydropower and improve energy efficiency. In our previous work, a Francis turbine was used in the water supply systems of high-rise buildings to properly control water pressure inside the pipeline and recover excess water energy. In this paper, an optimization study of the volute for the sectional shape, design method, inlet parameters, outlet width, and tongue was conducted using numerical simulations to improve the hydro turbine performance. The simulated results show that a circular section could better enhance the flow velocity inside the volute and make the flow velocity distribution more uniform at the volute outlet, and the equal mean velocity method is a more suitable volute design method in this special condition. The results of range analysis show that the water head reduction increases significantly with the increase in the inlet height, and both inlet height and outlet width have a significant effect on the efficiency. In addition, in the tongue optimization, a larger tilt angle corresponds to smaller output power and water head reduction; a larger stretch length in the limited angle range corresponds to larger output power and lower efficiency. Ultimately, the output power of the hydro turbine was increased by 18.65% and the efficiency by 2.1% through the volute optimization. [ABSTRACT FROM AUTHOR]

With the increasing popularity of clean energy, the use of micro turbines to recover surplus energy in the water supply pipelines of high-rise buildings has attracted more attention. This study adopts a predictor model based on Radial Basis Function Neural Network (RBFNN) to optimize the draft tube shape for micro-Francis turbines. The predictor model is formed on a dataset provided by numerical simulations, which are validated by lab tests. Specifically, numerical investigations are carried out in the shape of a draft tube to determine an optimal model. Additionally, the superiority of the RBFNN model in nonlinear optimization is verified by comparing it with other models under the same date sets. After that, the design parameters are optimized using RBFNN and sequential quadratic programming algorithm (SQPA). Finally, the turbine prototype is fabricated and tested on a lab test rig. The experimental results indicate that the numerical method adopted in this research is accurate enough for such a micro-Francis turbine performance prediction. Under the design conditions, the proposed micro-Francis turbine produces a power of 147 W with an efficiency of over 29%, which shows a considerable improvement compared to the initial prototype. [ABSTRACT FROM AUTHOR]

Hydropower is Indonesia's second most significant renewable energy source, following solar energy. It possesses a substantial capacity of 75,000MW, constituting around 17.8% of the overall renewable energy portfolio in the country. However, hydropower installations in Indonesia account for only 0.061% of the available potential, leaving a considerable gap. One effort to bridge the gap is the development of a water turbine. Because Savonius has been a popular turbine in recent years, this research was conducted using one. Because of the Savonius's simple structure, it is simple to modify. This study aims to determine how the number and size of fins affect the performance of the Savonius water turbine. Computational Fluid Dynamics with two-dimensional analysis was used in this study. The Fluent Solver and the Ansys Student version software were used in this study. The variations included no fins, one fin, and two fins on the rotor. The k-shear Stress Transport (SST), which produces accurate findings by combining the k-model for free flow and the standard k-model for boundary (wall) flow. Inlet velocities of 0.3m/s, 0.65m/s, and 0.9m/s were utilized for the research simulations. At a flow velocity of 0.65m/s and a TSR of 0.77, the power coefficient is increased by 13.8% by adding two fins compared to the configuration without fins. The findings were subsequently subjected to a two-factor factorial design analysis. The findings indicate that the number of fins and the TSR factor exert a substantial impact. However, two factors have no influence on each other. [ABSTRACT FROM AUTHOR]

Abstract: There is a growing interest in utilizing tidal currents for power generation which has led to extensive research on this source of renewable energy. The amount of energy that can be extracted from tidal currents has been a topic of considerable interest to researchers for many years; still, there is no consensus on the extent to which this resource can be exploited. A turbine generates no power if it presents no resistance to the flow or if it presents so much resistance that there is no flow through it. At the same time, the estimation of exploitable resource should take into consideration the environmental, economic and social constraints. In view of these, the design of efficient turbines driven by bi-directional tidal currents has been a challenge to researchers for some time. There appears to be a general agreement among researchers that a number of turbines spread over the width of the channel can extract more energy compared to an isolated turbine. The present work is aimed at quantifying the improvement in the performance of a given type of turbine by utilizing a larger area of the channel. Numerical experiments were performed using the commercial CFD code ANSYS-CFX to study the performance of a bi-directional cross-flow turbine by simulating two cases of i) a single turbine and ii) a number of equally spaced turbines. It was found that the Coefficient of Power can be increased significantly by employing a larger area of the channel. [Copyright &y& Elsevier]

This study focuses on a DN50 pipeline-type Savonius hydraulic turbine. The torque variation of the turbine in a rotation cycle is analyzed theoretically in the framework of the plane potential flow theory. Related numerical simulations show that the change in turbine torque is consistent with the theoretical analysis, with the main power zone and the secondary power zone exhibiting a positive torque. In contrast, the primary resistance zone and the secondary resistance zone are characterized by a negative torque. Analytical relationships between the turbine's internal flow angle θ, the deflector's inclination angle α0, and the coverage angle α of the power zone are introduced, and a method for calculating the optimal number of blades is proposed to maximize the power zone. Results are presented about performance tests conducted on five groups of hydraulic turbines with the blade number ranging from 3 to 7. Such results indicate that both the turbine's recovery power and efficiency attain the highest values when the blade number is 4, which is in agreement with the number of blades calculated by the proposed method. Additionally, the study examines the effects of the flow rate on turbine parameters and the projected energy generation and cost savings for a specific pipeline configuration. [ABSTRACT FROM AUTHOR]

The purpose of this study is to analyze the rotational speed characteristics of a spherical turbine start-up process, and the rotational speed characteristic of the spherical turbine is studied by numerical simulation. In order to ensure the reliability of the numerical simulation, the numerical simulation results at different flow rates are compared with the experimental results, and the results show that it is feasible to investigate the rotational speed characteristics of the spherical turbine using numerical simulation. The numerical results demonstrate that the start-up process of the spherical turbine can be separated into two stages: the start-up acceleration stage and the transition stage, which are followed by periodic fluctuations of the rotational speed. In addition, when the flow rate is 8 m3/h , the spherical turbine can self-start under the load coefficient (Bg) if less than 3×10−5. If the Bg is larger than 3×10−5 , the turbine fails to start-up. The failed start-up shares characteristics: the turbine only moves forward and backward alternately in a small angular range. However, eventually, the applied load torque dominates, and the turbine starts to reverse. It is found that the flow rate and the turbine rotational speed present a linear relationship under the no-load operating condition. [ABSTRACT FROM AUTHOR]

Abstract  The development of a three-hole pressure probe with back-flushing combined with a conductivity probe, used for measuring simultaneously the magnitude and direction of the velocity vector in complex air–water flows, is described in this paper. The air–water flows envisaged in the current work are typically those occurring around the rotors of impulse hydraulic turbines (like the Pelton and Cross-Flow turbines), where the flow direction is not known prior to the data acquisition. The calibration of both the conductivity and three-hole pressure components of the combined probe in a rig built for the purpose, where the probe was placed in a position similar to that adopted for the flow measurements, will be reported. After concluding the calibration procedure, the probe was utilized in the outside region of a Cross-Flow turbine rotor. The experimental results obtained in the present study illustrate the satisfactory performance of the combined probe, and are encouraging toward its use for characterizing the velocity field of other complex air–water flows. [ABSTRACT FROM AUTHOR]

The present work considers the possibility of using river currents to generate electric power in order to supplement existing power units. A physical system consisting of a flowing river/canal with rectangular cross section, an open channel nozzle, and an impact turbine is modelled mathematically. The model is simulated using MATLAB for varying slopes and two nozzle-turbine sequences. It is found that the usage of nozzles demonstrably increases the velocity, and therefore, the kinetic energy of the flow. A total power ranging from 0.34 to 10.79 MW for the lowest and highest value of slope, respectively, is predicted by the model. Possible applications are discussed. [ABSTRACT FROM AUTHOR]

Turbine energy recovery is a process energy saving technology, and understanding turbine efficiency has important operational and economic benefits for the operator of a power plant. There are three main areas of research into turbine energy efficiency: the structural performance of the turbine itself, the configuration of the recovery device and the regulation of operating conditions. This paper summarizes recent research advances in hydraulic turbine energy efficiency improvement, focusing on the design factors that can affect the overall efficiency of a hydraulic turbine. To quantify the impact of these factors, this paper investigates the effects of surface roughness, flow rate, head and impeller speed on overall efficiency. Methods for optimizing improvements based on these design factors are reviewed, and two methods, the Box–Behnken Design method and the NSGA-II genetic algorithm, are described with practical examples to provide ideas for future research. [ABSTRACT FROM AUTHOR]

This work investigates the effect of channel blockage on the performance of axial and cross-flow turbines with the objective of filling a gap in the literature on suitable blockage corrections for cross-flow turbines. Our investigation is based on 3D computational fluid dynamics simulations at high Reynolds number. Blockage corrections are proposed for axial and cross-flow hydrokinetic turbines. These corrections allow the estimation of the drag, power and tip speed ratio of the theoretically unconfined turbine, based on results of the confined turbine. It is found that a blockage correction based on a simple linear momentum actuator disk theory, is quite adequate when applied to both axial and low-solidity cross-flow turbines. Results suggest that for the 3-bladed (high-solidity) cross-flow turbine, this method slightly underpredicts the correction factor, more so for drag than for power. Normalizing with the bypass flow velocity improves the drag correction. For both technologies, the power extracted is found to be almost insensitive to blockage when dynamic stall is present. To discriminate between lateral and vertical confinement is usually not required, the performance being mostly dependent on the blockage ratio (ratio of turbine and channel frontal areas) unless the confinement asymmetry differs by more than a factor of 3. [ABSTRACT FROM AUTHOR]

An investigation was undertaken into energy recovery from water supply systems (WSSs) using pumps that can work in reverse as turbines. Napoli Est network in Italy was selected as a case study. To find the optimal locations for the installation of reversible pumps in the network, a methodology was developed and implemented using computer programming and hydraulic simulation software. A technical feasibility analysis was conducted to create different scenarios for implementation and a suitable pump was designed using computational fluid dynamics. Pump mode and reverse mode operation were simulated numerically and the performance was improved. Financial analysis showed that energy production in WSSs using pumps as turbines is a profitable alternative to traditional turbines and a renewable solution for the world's growing energy needs. [ABSTRACT FROM AUTHOR]

In-pipe water turbines have begun to gain interest for harvesting power on a small scale from pipe networks. However, few studies have addressed the feasibility of installing spherical lift-based helical-bladed turbines in a water supply network. Points such as the pressure drop and generated power remain unexplored. In this study, a three-dimensional numerical model, based on OpenFOAM, is used to investigate the performance of the spherical lift-based helical-bladed in-pipe water turbine. The study aims to evaluate how the geometric properties of this turbine affect its performance in terms of power and efficiency, and the hydraulics of pipe flow in terms of pressure drop. The study considers a turbine of diameter 600 mm, with the following geometric properties: number of helical blades 3, 4 and 5; blade chord length 10%, 15% and 20% of turbine diameter D; blade helicity 0°, 60° and 120°; and pitch angle −6°, −3°, 0° and 3°. These parameters are analyzed at tip speed ratios (TSRs) of 2, 3 and 4. The results show that the five-blade turbine yields a power of 1300 W, while the three-blade turbine yields only 870 W, at an optimum TSR of 3. A change in the chord length of 50% (from 0.10D to 0.15D) increases the turbine power by 88.4% and efficiency by 40% for the same TSR. A further change to 0.20D gives no significant improvement in efficiency or power output. An increase in the helical angle from 0° to 120° results in a 22.8% reduction in turbine power. The turbine achieves the maximum power output of 1350 W at zero pitch angle, with a corresponding efficiency of 27%. The maximum head loss observed is 1.6 m, which represents 2.7% of the total head in the pipe. Solidity has a more pronounced effect on head losses than helicity and pitch angle. [ABSTRACT FROM AUTHOR]

Health monitoring devices are critical for the safe and reliable operation of water supply systems, but their chemical batteries are easily depleted. Thus, this paper developed a micro-vertical axis water turbine that converts part of the water head into electrical energy and supplies power for the monitoring device. The performance of four groups of micro-turbines was investigated in detail through experimental testing. Different from our previous study, the entire performance curves of micro-turbines at different rotation speeds and flow velocities were obtained in order to consider the wide range of flow velocities inside the real water pipeline. The feasibility of the designed turbines in the power supply system was verified by on-site testing. The experimental results show that different types and opening sizes of blocks have a distinct influence on the output power of micro-turbines. Each type of block has the corresponding optimal opening size to gain the highest performance. Within a certain range, the maximum output power varies linearly with the increase in flow velocity. In a specific flow velocity, the optimal rotational speed of the micro-turbine generated the maximum output power can be predicted by the power curve. In addition, through the experimental data, it is found that among all the measured turbines, the 12-blade hollow shaft turbine with a 90% eye-shaped block is the best one, with an output power of 88.2 W and an efficiency of 15.76%. Finally, the results of an on-site test are consistent with that of the experiment properly, which verifies the reliability of the measured data in the laboratory. [ABSTRACT FROM AUTHOR]

Crossflow turbines represent a valuable choice for energy recovery in aqueducts, due to their constructive simplicity and good efficiency under variable head jump conditions. Several experimental and numerical studies concerning the optimal design of crossflow hydraulic turbines have already been proposed, but all of them assume that structural safety is fully compatible with the sought after geometry. We show first, with reference to a specific study case, that the geometry of the most efficient impeller would lead shortly, using blades with a traditional circular profile made with standard material, to their mechanical failure. A methodology for fully coupled fluid dynamic and mechanical optimization of the blade cross-section is then proposed. The methodology assumes a linear variation of the curvature of the blade external surface, along with an iterative use of two-dimensional (2D) computational fluid dynamic (CFD) and 3D structural finite element method (FEM) simulations. The proposed methodology was applied to the design of a power recovery system (PRS) turbine already installed in an operating water transport network and was finally validated with a fully 3D CFD simulation coupled with a 3D FEM structural analysis of the entire impeller. [ABSTRACT FROM AUTHOR]

Purpose: In Southeast Asia, the renewable energy produced from hydropower systems has significant potential. Therefore, adequate development is needed to prevent future energy-related crises. This study, therefore, aims to determine the variations effects in geometry and the geometrical factors on turbine performance. Design/methodology/approach: The developed aspects are selected to determine the blade shape, its number and multistage requirements. The study was conducted in 3D simulation, with Ansys software used to calculate a series of computational fluid dynamic problems. The aspect ratio applied in this study utilized the ratio of the overall diameter of the rotor height (D / H), which is 1. Findings: The results showed that the highest Cp-max value, number of blades and stages were 0.2, two and three, respectively. Furthermore, these attributes combined to improve the performance of hydroturbines. Research limitations/implications: The research was fully conducted using numerical simulation, which requires sustainable research in the form of laboratory experiments. Also, pioneer experiments were conducted using benchmarking to ensure the results obtained are reliable. Practical implications: Hydropower is one of the best renewable energy sources in Indonesia with a large potential in the archipelago and tropical countries due to rivers and various water sources. The current generated is a useful reference for Savonius design. Originality/value: The originality of this study is to examine the three aspects of the geometry of the rotor, such as the number and shape of blades, as well as the stages in the same boundary conditions. Therefore, the comparison of the effects of changes in geometry on turbine performance is more acceptable and complete compared to the pioneer works, which focused on a parameter. This research combines several aspects to determine the effect of rivers and various water sources on the hydroturbine. [ABSTRACT FROM AUTHOR]

The excess hydraulic pressure in water supply network pipes is one of the major problems in design and implementation stages of these projects. To reduce the excess pressure and maintain network safety, a variety of pressure reducing valves are used, which waste all the excess pressure. However, having used the appropriate water microturbines, while reducing the pressure loss to an optimum value, the system could recover the wasted energy. In this study, numerical simulation and experimental investigation of microturbine in a water supply system have been performed to evaluate the electrical power generation capacity of an over‐pressured network. The numerical simulation of the microturbine was conducted using Ansys‐Fluent software. The microturbine has been experimentally investigated with different inlet flow rates, the effect of different post‐microturbine heads and also the effect of different opening angles of guide plate on its performance, three different scenarios were defined. Based on numerical simulation and laboratory results, the best performance of the microturbine was obtained when the inlet flow rate was 0.01184 m3 /s and also opening angle 20° for the guide plate, in which the microturbine output was equal to 59.01 W. The generated power by the microturbine can meet the electrical needs of sensors and other network monitoring equipment. [ABSTRACT FROM AUTHOR]

The characteristics of the fluid–structure interaction on the flexible blades of a horizontal-axis water turbine are studied; this bioinspired technology features mechanical simplicity, performance and lifetime improvement, and low fish impact risk, all characteristics of a truly sustainable renewable energy exploitation. A surface-tracking method synchronized with force measurements was applied on a surrogate model of single-bladed, vertical-axis water turbine in a water channel. This allows for the characterization of the structural deformations and their link to the hydrodynamic forces, over a large range of turbine designs and operating points. It is shown that the phase angles of the maxima in blade deformation coincide with those of the load maxima on a rigid blade in identical flow conditions. The influence of the turbine's tip/speed ratio on the blade deformation and blade load is investigated. With the chosen blade design, hydrofoil deformation is found to be maximum in the operating points where the performance improvement is maximized ( k o = 0.3 ). With lower values of reduced frequency (corresponding to lower rotation speed), fluid-induced forces dominate the fluid–structure interaction. Conversely, at higher frequencies, structural inertia dominates the interaction, and blade deformation is again reduced. Results suggest that the optimal blade rigidity may depend on the operating point; nevertheless the potential of the flexible-blade design is demonstrated through clear linking of fluid-induced forces and blade deformation in the complex flow conditions of the Darrieus water turbine. [ABSTRACT FROM AUTHOR]