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• A novel inverted cross-flow turbine and its design method for the low and ultra-low head hydraulic condition were proposed. • The four-step parametric studies were conducted to achieve the optimized turbine design. • The turbine achieved higher than 60 % efficiency range in the ultra-low head condition (under 3 m water head) by using a simple spiral nozzle and without a guide vane. • The optimized turbine maximum efficiency was achieved 72.92 % efficiency at the turbine speed 170 RPM with 8.01 m of water head. This study aimed to address the challenges of micro-hydropower generation in low-head environments to expand the proportion of hydropower in renewable energy and achieve a carbon neutrality policy. To achieve these goals, various factors affecting the micro-hydro systems, including geographical constraints, construction costs, and grid connectivity, were reviewed and assessed. The results concluded that a novel type of cross-flow turbine with inverted structures, improved the economic feasibility, productivity, and installability of micro-hydropower plants by reducing head losses in open channels or small streams. The parametric studies consisted of four steps: first, designing the initial inverted cross-flow turbine based on the traditional design rules; for the second and third steps, a parametric study for comparing the runner diameter ratio and the number of blades is conducted; and in the last step optimized turbine was designed. The best efficiency point of the optimized inverted cross-flow turbine was 72.92 % at a runner rotational speed of 170 RPM with a 0.75 runner diameter ratio and 35 blades. The optimized turbine was improved by 7.8 % in power and 7.35 % in efficiency, higher than the initial turbine. From the hill chart comparison between the initial and optimized turbine, operation range expansion was confirmed. Overall, this research demonstrates the potential of the inverted cross-flow turbine under low-head conditions. [ABSTRACT FROM AUTHOR]

Cross-flow turbines harness kinetic energy in wind or moving water. Due to their unsteady fluid dynamics, it can be difficult to predict the interplay between aspects of rotor geometry and turbine performance. This study considers the effects of three geometric parameters: the number of blades, the preset pitch angle, and the chord-to-radius ratio. The relevant fluid dynamics of cross-flow turbines are reviewed, as are prior experimental studies that have investigated these parameters in a more limited manner. Here, 223 unique experiments are conducted across an order of magnitude of diameter-based Reynolds numbers (≈ 8 × 1 0 4 – 8 × 1 0 5 ) in which the performance implications of these three geometric parameters are evaluated. In agreement with prior work, maximum performance is generally observed to increase with Reynolds number and decrease with blade count. The broader experimental space clarifies parametric interdependencies; for example, the optimal preset pitch angle is increasingly negative as the chord-to-radius ratio increases. As these experiments vary both the chord-to-radius ratio and blade count, the performance of different rotor geometries with the same solidity (the ratio of total blade chord to rotor circumference) can also be evaluated. Results demonstrate that while solidity can be a poor predictor of maximum performance, across all scales and tested geometries it is an excellent predictor of the tip-speed ratio corresponding to maximum performance. Overall, these results present a uniquely holistic view of relevant geometric considerations for cross-flow turbine rotor design and provide a rich dataset for validation of numerical simulations and reduced-order models. [Display omitted] • Experimental parameter space unifies narrower prior work on cross-flow turbines. • Optimal chord-to-radius ratio decreases as diameter-based Reynolds number increases. • Optimal preset pitch angle becomes more negative as chord-to-radius ratio increases. • Turbines with more blades have lower efficiency, but more uniform power and forces. • Turbines with the same solidity do not always have the same maximum efficiency. [ABSTRACT FROM AUTHOR]

A novel vertical augmentation channel housing a direct-drive cross-flow turbine, with nozzles on both the sides of the turbine, was designed and an optimized configuration was obtained. The geometries of the guide nozzle and the front nozzle were optimized under steady flow conditions. The performance of the cross-flow turbine was analyzed using commercial computational fluid dynamics (CFD) code ANSYS-CFX. The optimized design was then evaluated as a wave energy converter both experimentally and computationally. The waves in the numerical wave tank (NWT) were generated using a piston type wave-maker. The optimized design gave a maximum output power of 13.2 W and an efficiency of 48.31% at a wave height of 0.2 m and wave period of 2.75 s for a rotational speed of 35 rpm. The difference between numerical and experimental efficiencies was within 3.5%. In addition to this, particle image velocimetry was used to study the flow characteristics in the augmentation channel and the turbine. The results show that the CFD code captures the flow in the augmentation channel and around the turbine accurately. The optimized design, which occupies less space than other wave energy converters, can be used to efficiently harness energy from the waves. [ABSTRACT FROM AUTHOR]

Understanding the effect of tidal turbines on local erosion of the estuarine bed is crucial for design and maintenance of turbines with stable foundations and assessment of their environmental impacts. This report describes the results of flume experiments on clear-water scour caused by a single cross-flow turbine in steady flow conditions. The turbine investigated is a Momentum Reversal Lift (MRL) turbine originally designed in collaboration with the University of Exeter. Results show that the turbine can cause significant bed scour, particularly when it was not spinning and in a particular orientation of blades. This is opposite to the previous findings for axial flow turbines. The bottom plate of the turbine, although increasing scour depth, was found to increase the turbine performance and reduce adverse effects on the downstream flow. The findings highlight the importance of regular monitoring and taking immediate repair actions for a tidal installation. • Flume experiments on clear-water scour for MRL of cross-flow turbine. • The MRL turbine produces significant downstream scour. • Regular monitoring of the turbine to ensure it is operating properly is important. • Turbine runs slower without the bottom plate. • Temporal evolution of scour reduces the rotational speed of the turbine. [ABSTRACT FROM AUTHOR]

The present work reports CFD based investigation of the effect of design parameters on the flow velocities of a cross flow turbine (CFT). Best described as an impulse type turbine with partial admission of air, cross flow turbines meet the demand for an efficient turbine to run at low head that is also easy to manufacture. The design of cross–flow turbine is unique due to the generation of power during two stages. This type of turbine is often used in small hydropower plants located in less–developed countries. The design parameters of CFT that can be varied to increase overall efficiency and power output of the turbine are water inlet angle, blade angle at inlet and outlet. In the present work the design parameters are varied for different nozzle openings and simulated using CFD. A full 3-D steady state flow simulation of the cross-flow turbine is performed including casing, runner and nozzle assembly. [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]

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]

This study attempts to improve the efficiency of a given type of cross flow turbine by supplying air from air suction holes. A newly developed air supply method is adopted. CFD analysis of the cross flow turbine is carried out to investigate the performance and internal flow characteristics of the turbine in detail. The air layer prevents shock loss between water flow and axis and suppresses recirculation flow in the runner passage. Hence, it is necessary to measure the amount of air layer in the runner passage and examine its effect on the performance of the cross flow turbine. The result shows that the turbine efficiency has improved more as the newly developed air supply method is applied effectively. [ABSTRACT FROM AUTHOR]

In this work we study experimentally the flow dynamics inside the rotor of a three straight-bladed Cross-Flow Turbine (CFT). The CFT model used in the experiments is based on symmetric NACA-0015 profiles, with a chord to rotor diameter ratio of 0.16. The turbine model was designed in order to quantify the flow inside and around the rotor using planar Digital Particle Image Velocimetry (DPIV). Tests were made by forcing the rotation of the turbine with a DC motor, which provided precise control of the Tip Speed Ratio (TSR), while being towed in a still-water tank at a constant turbine diameter Reynolds number of 6.1 × 10 4 . The range of TSRs covered in the experiments went from 0.7 to 2.3. The focus is given to the analysis of the blade-wake interactions inside the rotor. The investigation has allowed us to relate the interactions with the performance differences in this type of turbines, as a function of the operational tip speed ratio. [ABSTRACT FROM AUTHOR]

One key factor in the exploitation of tidal energy is the study of interactions of turbines when working in tidal turbine farms. The Momentum Reversal and Lift (MRL) turbine is a novel cross flow turbine. The three blades rotate around a common central horizontal axis which is parallel to their own axis and perpendicular to the flow. The novelty of the MRL turbine is that it relies on the combination of both lift and momentum reversal (drag) for energy extraction. Scaled MRL turbine models of 0.164 m in diameter were used to characterise the flow in three different tidal array settings. Detailed maps of axial velocity profiles and velocity deficits downstream of the turbine are presented, enabling the visualisation of characteristic flow patterns. The results show that the MRL generates lower velocity deficits and turbulence intensities in the near wake than those associated with horizontal axis turbines. The downstream wake was not completely symmetrical which was related to the geometry of the device but also due to the flow developed in the flume. Amongst the three array configurations studied, a fence of turbines with the lowest separation provided the highest power output. [ABSTRACT FROM AUTHOR]

A detailed wake analysis of two different turbine concepts is conducted to gain a fundamental understanding of the main energy recovery processes at play in each case. An axial-flow turbine and a cross-flow turbine are considered. Both operate near their respective optimal efficiency conditions in a uniform oncoming flow and at a Reynolds number of 10 7 . Three-dimensional Delayed Detached-Eddy Simulations (DDES) are carried out and the time-averaged Unsteady Reynolds-averaged Navier–Stokes (URANS) equations are used as a post-processing tool in order to assess the importance of the various contributions affecting the wake recovery quantitatively. It is found that the dominant mechanism is fundamentally different between the two turbine technologies. Indeed, while the axial-flow turbine's wake is strongly influenced by an instability phenomenon leading to a significant turbulent transport, the cross-flow turbine's wake recovery is found to be much more related to the mean spanwise velocity field. As a result, unlike the axial-flow turbine's wake dynamics which is highly dependent on the turbulent characteristics of the oncoming flow, the cross-flow turbine's wake is expected to be less sensitive to these turbulent characteristics but highly dependent on the geometric characteristics of the turbine such as the turbine's aspect ratio. [ABSTRACT FROM AUTHOR]

Micro hydrokinetic energy scheme presents an attractive, environmentally-friendly and efficient electric generation in rural, remote and hilly areas. However, this scheme is yet to be fully discovered, as researchers are still searching for solutions for the main problems of low velocity of current in the open flow channels and low efficiency of hydrokinetic turbines. This research proposes a novel system configuration to capture as much kinetic energy as possible from stream water current. This system, known as bidirectional diffuser augmented (BDA) channel, functions by utilizing dual directed nozzles in the flow and is surrounded by dual cross flow/Banki turbines. It is also important to obtain the efficient design parameters of the turbines to use in the current configuration. The appropriate angle is important in order to guide the flow to touch the blades more perpendicularly to capture as much torque and power as possible. Hence, experimental and numerical investigations have been carried out in this research paper to study the performance characteristics of the CFT configuration applied in BDA system and investigate the effects of blades' inlet and outlet angles of CFT runners on the internal flow characteristics and efficiency. In this study, four different runners with various inlet and outlet angles of two CFT have been investigated. The CFD results have been validated with the experimental work and proven acceptable with flow pattern and performance characteristics. The results of the current study conclude that the maximum power coefficients (Cp) of 0.612 and 0.473 for lower and upper turbines are recorded for best runner angles of Case 3. [ABSTRACT FROM AUTHOR]

Micro hydro power plant offers the cheapest renewable as well as a clean energy resource having abundant room for development. Cross flow turbine is easy to manufacture and maintain, operable in off-grid remote areas with negligible civil work requirement leading to its high popularity in developing countries. The present study numerically investigates the effect of different blade design parameters on the performance of hydraulic cross flow turbine using Ansys-CFX®. Firstly, a comparative analysis of the full turbine and half turbine model is performed. Then, the blade leading and trailing edge is varied considering four distinct geometric profiles with varying rotational speeds of 100–240 rpm. Moreover, the blade exit angle is varied from 50° to 100°, keeping a consistent rotational speed of 180 rpm. The results are presented in terms of the torque generated, and the turbine efficiency. In addition, the localized flow around the blades is elaborated using the flow velocity contours and streamlines. The geometric combination with a circular profile for the blade leading edge followed by a sharp trailing edge transpired maximum turbine efficiency. Moreover, the optimal blade exit angle lies between 55° and 60° contrary to the general practice of radial exit. • Micro hydro power plants provide the cheapest clean and renewable energy. • Cross flow turbines are the easiest to manufacture and maintain powering MHPP. • Blade design parameters of the cross flow turbine are investigated using Ansys-CFX®. • The developed model is validated with the experimental results. • Acute blade exit angle is proposed contrary to radial exit. [ABSTRACT FROM AUTHOR]

Abstract: This work details the implementation of a modified Beddoes Leishman model into a Free Vortex Method (FVM) to predict the performance of Darrieus turbines. The model uses Sheng''s consideration of the reduced pitch rate influence on the dynamic loads over the foil and revised Kirchhoff flow equations to calculate lift and drag at extended ranges of angles of attack. A simple consideration of the Reynolds number cyclic variation on the blades characteristic of the Darrieus turbines is also implemented. Comparison with published and experimental data at a range of chord to radius ratio shows good agreement. [Copyright &y& Elsevier]

• 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]

While studies on horizontal axis tidal turbines are plentiful, those on ducted twin vertical axis alike HydroQuest's turbines are lacking. For such a device, both the relative counter-rotation direction of the rotors and the tripod base geometry upstream are different between ebb and flood tide. Consequently, this paper analyses the effect of the two opposed flow directions on the hydrodynamic performance and on the wake of the turbine. The study is based on experimental measurements at a 1/20th scale in Ifremer's wave and current flume tank. The hydrodynamic performance of the model are characterised over a wide range of operating points with the turbine installed on a tripod and on a monopile base. In addition, the 3D wake of the turbine is thoroughly analysed in the two flow directions using 3-component laser Doppler velocimetry. Overall, the drag and the maximum average power coefficient are not affected by the current direction but the optimal tip speed ratio is 7 % lower during ebb with 1.5 times higher power fluctuations compared to flood tide. Besides, the wake of the two rotor columns interact differently depending on the flow direction, leading to a 30 % faster surface averaged velocity recovery in the flood tide configuration. The observed effect of flow direction provides a better knowledge of twin vertical axis turbine wake interactions and highlights the impact of the gravity base geometry on the development of the overall turbine wake. This paper also provides a wide experimental database for the validation of numerical models applied to ducted twin-vertical axis tidal turbines. • Ebb and flood tides modelled experimentally in a tank by turning the turbine around. • Twin vertical axis turbine (2-VATT) mean power is barely affected by the flow direction. • Gravity based 2-VATT power fluctuation and wake development depend on base geometry. • Rotors wake merging distance and recovery depend on the counter-rotation direction. [ABSTRACT FROM AUTHOR]

Abstract Cross-flow turbine blades operate in an unsteady environment over large ranges of angle of attack and Reynolds number, often enduring dynamic stall. The hydrodynamics are further complicated because the circular orbit of the blades changes their effective curvature. In order to address these technical challenges with modeling cross-flow turbines, this article presents a novel dynamic stall model with flow curvature correction. The dynamic stall model extends Beddoes-Leishman dynamic stall theory, including several effects such as proper asymptotic behavior at large (∼90°) angles of attack, influence of reduced-pitch rate on the stall angle, dynamics of the flow separation point, and changes in effective camber due to flow curvature. Further, the model enables rapid hydrodynamic analysis of cross-flow turbines using free vortex methods. Important design parameters such as blade thickness and camber are explicitly accounted for in the model, which enables parametric study of turbine configurations and therefore makes the model useful for system-level turbine optimization. Numerical predictions are validated by experimental data for several cases, including ranges of blade profile, toe angle, solidity, and tip speed ratio. Highlights • A dynamic stall model in discrete vortex method was implemented for cross flow turbines. • Experimental data was acquired for a two blade test cross flow turbine. • The analytical model results were compared with published and experimental data. [ABSTRACT FROM AUTHOR]

Marine hydrokinetic turbines are a promising source of renewable energy, but the costs of existing cross-flow turbine designs are too high. In order to develop new designs with reduced costs, there exists a need for a low-order computational model that is simultaneously fast, accurate, and robust. Herein, we present a novel theoretical model for the analysis of cross-flow propellers and turbines based on the vortex lattice method (VLM). In order to overcome the limitation that the VLM ignores viscous effects (such as trailing-edge flow separation), we present a novel method to account for viscous-thickness-load coupling (VTLC). In order to overcome the difficulty that wake passages cause the VLM to be unstable, we present the panel-averaged induced velocity for the influence of wake vortices on the blades. Herein, we describe our model and provide verification versus RANS CFD. Results show that our VLM + VTLC model predictions are three times more accurate than prior low-order models (i.e. three times lower root mean square error to high-fidelity RANS results) yet 10,000 times faster than RANS over a wide range of operating conditions. Image 1 • Cross-flow turbomachines are modeled via vortex lattice method (VLM). • Viscous-thickness-load coupling (VTLC) is derived to model viscous effects. • VTLC accurately models loss in lift due to trailing-edge flow separation. • VLM + VTLC yields fast and accurate predictions of cross-flow turbomachine performance. [ABSTRACT FROM AUTHOR]

Highlights • A novel design method for inline cross-flow turbine used in water mains was proposed. • Effects of different block design on turbine performance were investigated. • The influence mechanism of block shape on turbine performance was studied by numerical methods. Abstract Cross-flow turbines offer a promising, cost-effective solution to harvest hydropower from water mains to supply power to water monitoring systems. However, the design and performance of cross-flow turbines in water mains have not been fully investigated. In this paper, an inline cross-flow turbine configuration with two blocks is proposed and a block design method is presented. Specifically, numerical investigations are carried out to verify the proposed method and study the effect of different block designs on turbine performance. Flow velocity analysis shows that the proposed block can improve the flow attack angle at the runner inlet and significantly increase the flow velocity through the runner. In addition, the pressure distribution indicates that the blocks can increase the pressure difference through the runner and thus improve turbine performance. A comparison of three models with different guide block orientation angles reveals that the model with the largest conversion block orientation angle performs best, because the blocks from this model not only function better in terms of flow separation and negative torque reduction at the first stage, but also convert more water head into kinetic energy. Numerical results show that the inline turbine can achieve its maximum efficiency of 42.4% with a power output of about 1500 W and that the water head reduction is limited within an acceptable range. [ABSTRACT FROM AUTHOR]

Using delayed detached-eddy simulations, the objective of this paper is to show the effects of some design parameters on the wake recovery of vertical-axis turbines. To that end, the wake dynamics of a single-blade turbine is analyzed and compared for two different positions of blade attachment point and for two designs of blade support structures (struts). The results show that the chordwise position of the blade attachment point affects the temporal evolution of the blade circulation during the turbine revolution. More precisely, we demonstrate that an attachment point positioned near the trailing edge of the blade leads to a temporal vorticity distribution that is detrimental to the wake recovery. Moreover, we show that the use of tip struts, that are highly beneficial to the turbine efficiency, affects the spatial distribution of the vortex structures shed by the turbine as well as the wake recovery. The results presented in this paper suggest that the velocity recovery in the wake is highly dependent on the very near-wake vortex dynamics. Therefore, we can infer that any geometric parameter affecting the temporal and spatial distributions of the vorticity shed by the blades can significantly alter the wake recovery of vertical-axis turbines. [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]

In the present work, Delayed Detached-Eddy Simulations (DDES) are conducted to evaluate the performance of an H-Darrieus vertical-axis turbine with detached end-plates, namely stationary end-plates that are not in contact with the turbine blades. More precisely, the force and the power coefficients of the turbine are analyzed for two different geometries of detached end-plates. The turbine wake dynamics is also presented and the main mechanisms responsible for the wake recovery rate are assessed. The results show that the presence of detached end-plates significantly increases the efficiency of the vertical-axis turbine considered. In addition to this improved efficiency, a semi-annular shape of detached end-plate leads to an improved recovery of the mean streamwise velocity in the turbine wake. The important wake recovery rate in the near-wake of the turbine with semi-annular detached end-plates is mainly related to the transport of momentum by the mean spanwise velocity field, which is also known to be the dominant contribution to the wake recovery rate of a turbine without detached end-plates. The results presented in this paper confirm that detached end-plates have a great potential to improve the performance of H-Darrieus vertical-axis turbines used both individually and within turbine farms. • The use of detached end-plates improves the efficiency of vertical-axis turbines. • Detached end-plates affect importantly the vorticity dynamics in the turbine wake. • The use of semi-annular detached end-plates improves the turbine wake recovery rate. • Transport of momentum by the mean spanwise velocity governs the wake recovery rate. [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]

Abstract During the boreal summer of 2015, a full-scale hydrokinetic turbine was deployed in the Kvichak River (Alaska), delivering electricity to the village of Igiugig. Here, quantification and analysis of the hydrodynamic modifications in the river caused by the turbine are presented. Field observations are used to produce a unique three-dimensional data set of fluid velocities in the vicinity of the turbine before and after turbine deployment. Three dynamic regions are distinguished in the wake. There is an induction zone just upstream of the turbine, where velocities decrease and turbulence increases. There is a near wake just downstream of the turbine, where the reduced velocities recover slightly and the elevated turbulence decays rapidly. Finally, there is a far wake well beyond the turbine, where reduced velocities are persistent and turbulence remains elevated. The results are used in a coarse energy budget for the river, including quantifying the total energy dissipated by turbulence in the near wake. This wake dissipation is found to be almost as large as the energy extracted for electricity generation, even when the turbine is not operational. Highlights • Unique data set of flow conditions around a full-scale hydrokinetic turbine. • Persistent turbine wake observed, with no recovery downstream of the turbine. • Similar operational and non-operational turbine wakes. • River energy loss in the turbine wake is comparable to the energy delivered to the grid by the turbine. [ABSTRACT FROM AUTHOR]

Abstract Three-dimensional steady-state RANS simulations of the flow around a stationary finite-span blade have been carried out. The analysis is directed toward the vorticity dynamics, the forces acting on the blade and their spanwise distributions when using end-plates or detached end-plates, namely end-plates that are not in contact with the blade tips. The objective is to understand the physics at play in the vicinity of the blade tips with an emphasis on the detached end-plates, as the use of such devices could be beneficial for optimizing the performance of vertical-axis turbines. This paper also aims at providing simple guidelines regarding the use of end plates and detached end-plates. The results show that the presence of detached end-plates leads to an important increase of the blade lift coefficient in addition to a significant reduction of its drag coefficient. This is explained by the fact that the detached end-plates modify the path of the vorticity lines shed by the blade, thus affecting the vorticity distribution and the resulting circulation along the blade. This work also shows that the forces on the blade are more sensitive to the dimensions of the detached end-plates in the transverse direction than to any other geometric parameter. Highlights • Both end-plates and detached end-plates strongly affect the forces on a blade. • Detached end-plates alter the distribution of the vorticity shed in the wake. • Detached end-plates do not affect the total circulation of the trailing vortices. • The forces are mainly sensitive to the transverse dimensions of the end-plates. [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 effect of blade profile on the efficiency of a waterfall cross-flow hydro turbine was investigated numerically using the non-uniform, thin, and standard blades. Each efficiency of the blade profile was evaluated by varying the tip-speed ratio (=0.3–0.9) and off-axis distance (=0.26–0.48), which are the influential parameters for characterizing the performance of the cross-flow turbine. Although a minor improvement was observed in the peak efficiency 62–63 % by the blade-profile effect, the off-peak efficiency was highly improved up to 8 % on the non-uniform blade and 11 % on the thin blade. The examination of the local and average torque distribution in reference to the flow fields showed that an increased torque on the non-uniform blade was observed at small blade angles due to the increased waterfall impingement, while that on the thin blade was observed at large blade angles caused by increased rebounding flow. This suggests the different torque enhancement mechanism of the cross-flow turbine on the non-uniform and thin blades in comparison with the standard blade. [ABSTRACT FROM AUTHOR]

The cross-flow turbine is an attractive technology for small-scale hydropower generation thanks to its low capital cost and relatively high efficiency even under partial discharge operating conditions. It has been proposed that this kind of turbine can be manufactured from standard steel pipe sections given its simple geometry, an alternative that would further decrease the turbine's capital cost compared to highly engineered cross-flow designs. This article explores the trade-offs encountered during the design of cross-flow turbines under the constrains imposed by the discrete set of dimensions available for commercial steel pipes. First, the computational model is presented, analyzed in terms of its convergence behavior, and validated with experimental data. Then, a parametric analysis is performed to understand the relative importance of the design variables and their optimum value in regard to the turbine efficiency. Based on the design guidelines derived from the parametric analysis, an example cross-flow turbine design is presented and thoroughly characterized, demonstrating that it is possible to engineer a cross-flow turbine of competitive efficiency out of commercial steel pipes. These guidelines may encourage the use of cross-flow turbines as an appropriate technology for off-grid regions. • A cross-flow turbine design methodology is presented. • The numerical model is characterized and then validated with experimental data. • The influence of the main design parameters on the efficiency is investigated. • Design guidelines and insight are drawn based on the parametric analysis results. • A cross-flow turbine design example is characterized throughout its operating range. [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]

Since the energy of ocean wave exists mostly near the water surface and decreases exponentially with depth, the resource of wave energy is measured in the line density unit (kW/m). Therefore, in the scaling up of a wave energy converter, the captured wave energy increases slowly in proportion to the wave front width of the device while its cost tends to increase in a pace faster than the square of device size. To overcome the problem, the authors propose a drag type cross-flow water turbine with its rotational axis lying horizontally and parallel to the wave front. Since the device will be light-weight and linearly extendable in the wave front direction, the larger (longer) converter can obtain the merits of scale for higher economic performance. The shape of proposed turbine is not axisymmetric for directly utilizing the orbital fluid particle motion in wave. The basic unit of the device is compact and the diameter of turbine is in the order of wave height. Two-dimensional flow simulation of the device in regular wave demonstrates the mechanism of the turbine and provides its preliminary performance prediction. [ABSTRACT FROM AUTHOR]

The performance of a high-solidity H-Darrieus cross-flow hydrokinetic turbine was tested in the subcritical flow of a narrow artificial canal. Turbine shape and swept area were selected to generate high blockage into the flow for mechanical power maximization, although a high axial thrust on the blades was attained. A detailed description of the support structure, probes, and the turbine is provided as a first step of further in-depth studies. After measurements of the undisturbed flow velocity with an acoustic doppler velocimeter, the turbine was submerged to operate at different rotor speeds, while measurements of torque, thrust, and rotor speed were acquired. The water depth at another crossbar was measured continuously to check the backwater profile spreading towards upstream, showing no flooding risk at each rotor speed. Experimental data were analyzed for the torque ripple investigation and high sensitivity to low tip speed ratios was demonstrated. • Setup of turbine testing in a canal, probes description and support structure. • A backwater profile is visualized upstream of the turbine at each rotor speed. • Averaged thrust, torque and power are illustrated with respect to the rotor speed. • The torque ripple phenomenon is investigated at a varying tip speed ratio. [ABSTRACT FROM AUTHOR]

Abstract Cross-flow turbine is a promising device for power supply to water monitoring sensors and meters along water supply pipes. In the previous research, an inline cross-flow turbine is proposed and the effects of blocks on turbine performance have been studied by numerical methods. Based on the results, mismatching exists between the flow inlet angle and blades outer angle, which may result in shock loss and flow separation. In this study, a numerical investigation was performed to study the effects of blades outer angle on the turbine performance. Results indicated that the matching between flow inlet angle and blades outer angle can enhance the torque output of runner first stage and significantly improve the overall turbine performance. To achieve a balance between turbine efficiency and water head reduction, the blades outer angle of the inline cross-flow turbine is suggested as 30°. [ABSTRACT FROM AUTHOR]

Water leakage monitoring system is essential for the urban water supply, but it is a great challenge to ensure stable and reliable power supply for this system. In this study, an inline cross-flow turbine was proposed to harvest hydropower from the water pipes. A numerical investigation was conducted to study the effects of blocks on the turbine performance. The simulation results indicated that the proposed upstream and downstream blocks can act as nozzle and diffuser in traditional cross-flow turbine to enhance the flow velocity and pressure difference through the impeller, so the turbine performance can be improved. The maximum output power of the turbine can research 136W when the TSR is 1.2 and the water head loss through the water turbine is in the range of 3.45m-3.75m water head, which has little negative impact on the normal water supply. [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]

The impact of the blade support structures (the struts) on the performance of vertical-axis turbines at a high Reynolds number is investigated here. Numerical simulations of a single-blade turbine with different strut configurations are carried out and the results are compared to a reference hypothetical turbine without strut. The results show that the struts are less detrimental to the turbine efficiency if they are located at the tips of the turbine blade, rather than at other intermediate positions along the blade span. Moreover, for struts located at the blade tips, it is shown that using rounded junctions between the struts and the blade can lead to a significant increase in the turbine efficiency. Indeed, the best turbine configuration presented in this paper has an efficiency that is more than 20% larger than that of the reference turbine without strut. This important increase in the turbine efficiency can partly be attributed to the fact that the tip struts with rounded junctions act as efficient winglets, leading to a significant decrease in the induced drag on the turbine blade. The results presented show that well-designed blade support structures can be very beneficial to the performance of vertical-axis turbines. • The spanwise position of the struts affects the vertical-axis turbine efficiency. • Struts located at the blade tips are less detrimental to the turbine efficiency. • Rounded blade-strut junctions are highly beneficial to the turbine efficiency. • Rounded blade-strut junctions allow to decrease the induced drag on the blades. [ABSTRACT FROM AUTHOR]

Abstract: A cross-flow turbine, also known as Banki turbine, is a hydraulic turbine that may be classified as an impulse turbine. It has gained interest in small and low head establishments because of its simple structure, cost effectiveness and low maintenance. The present work expands on this idea and aims to implement a cross-flow turbine as Direct Drive Turbine (DDT) for wave power generation. Waves have enormous amount of energy which is environment-friendly, renewable and can be exploited to satisfy the energy needs. A Numerical Wave-tank (NWT) was used to simulate the waves using the commercial CFD code ANSYS-CFX. The base model was firstly studied at five different wave periods without the turbine. The highest water power (PWP) of 32.01W was recorded at T=3s. A cross-flow turbine was then incorporated and the simulation was validated at T=2s. In addition to this, the performance of the turbine at T=2.5s and T=3s at different turbine speeds was also studied. The highest turbine output power of 14W was recorded at a turbine speed of 30rpm at the wave period of 3s, giving a turbine efficiency of 55%. [Copyright &y& Elsevier]

Despite a lot of optimism about the potential of hydrokinetic turbines in rivers, the reality is that very few are currently deployed in rivers, delivering power to those who need it. Barriers to their widespread deployment include, above all, the cost per kW actually delivered in rivers which rarely flow at more than about 1 m/s, far short of the 3 m/s at which rated power is typically quoted. Although designers of grid-connected systems aim for maximum annual energy yield, small off-grid systems with limited storage capacity should generally aim for minimum cost per continuous kW delivered. A further factor is that few fast-flowing rivers are deep enough to accommodate axial flow turbines greater than about 1 m diameter. A source of confusion and erroneous power prediction is the mistaken assumption by some researchers that hydrokinetic turbines are "zero head" turbines. Finally, there is a lack of interaction between researchers, who may have the necessary theoretical knowledge but lack awareness of real conditions, and potential users who may have the necessary hands-on practical skills but lack theoretical knowledge. This paper examines these factors, suggests measures to address them and describes a simple low-cost horizontal axis cross flow turbine with much greater swept area and able to generate more power than an axial flow turbine of similar diameter. [ABSTRACT FROM AUTHOR]

Abstract In a previous work we investigated the effectiveness of combining the concentration effects generated by a dual-pitched roof and a convergent-divergent semi-diffuser placed over a cross flow turbine (CFT), which is rooftop mounted with horizontal shaft running close to the roof ridge. By means of 2D CFD we now assess the effects of the upstream buildings on the performance of this concentration system. Three different urban layouts are simulated via a challenging fully-resolved URANS approach that gives unprecedented insight into the complex interactions of the flow around buildings, diffuser and turbine's blades. A promising power augmentation of 40% with respect to the case without diffuser are obtained and the mechanism behind this performance enhancement are analysed. The beneficial effect of the diffuser on the torque fluctuations damping (∼60%) is also discussed. Important remarks on the load control strategy for diffuser-augmented CFT are finally presented. Highlights • The diffuser-shaped wall over the turbine improves C P by 40%. • The diffuser-shaped wall over the turbine cuts Torque Ripple Factor by 60%. • If upstream buildings shelter the target roof, the diffuser wall can rise the C P to an acceptable value. • The diffuser wall works relatively better under highly skewed winds. • Load control warning: in augmented systems TSR small decreases cause sudden C P drops. [ABSTRACT FROM AUTHOR]

In-pipe hydrokinetic systems employing spherical turbines that operate in confined flows with high blockage ratio are a relatively new technology. The number of modeling and computational studies analyzing the performance of spherical turbines operating in confined area is quite limited. The main objective of this study is to model a novel in-pipe cross-flow turbine and perform numerical analyses. Accordingly, a five bladed spherical rotor was designed and numerical simulations were conducted for various inlet velocities (0.8–6.5 m/s), tip speed ratios (0.6–5.2) and blockage conditions (0.59–0.83). The relationships between geometric, dynamic parameters and power performance were discussed. The findings showed that increasing blockage ratio significantly improved the power performance by shifting the C P -λ curve to the right-upward direction. The output power was maximized by a factor of 2.5 where the pipe diameter is reduced from 1.3 to 1.1 times the turbine diameter. A linearly increasing relationship was achieved between power coefficient and blockage where the angle was proportional with λ. Optimum λ was obtained around 4.2 at high blockage where it was mostly between 1.5 and 2 in free flow turbines. This research is expected to contribute to spherical turbine studies for optimal power generation and energy efficiency in water transmission pipelines. • Research on modeling and performance of in-pipe spherical turbines are limited. • A spherical in-pipe turbine was modeled based on cross-flow turbine literature. • Numerical simulations were conducted at various velocity and blockage conditions. • Linearly increasing correlation is obtained between power coefficient and blockage. • C P - λ curve shifts to right-upward direction at increasing blockage. [ABSTRACT FROM AUTHOR]

A Crossflow turbine is a device used to generate power from hydro, which is a renewable source of energy. The salient feature of this turbine is its simplicity in construction. In the past few decades, variables such as flow diverter, air holes, bidirectional flow were introduced in the turbine design to improve its efficiency. This paper presents a comprehensive review of the performance of the cross flow turbine. The review of literature is classified into experimental and numerical studies. The present study highlights the optimum range of geometrical variables required for the efficient design of a cross flow turbine. The study also emphasizes the importance of employing the cross flow turbine in remote places where run-of-river hydro power plants are feasible, as it provides a low-cost energy solution. The outcome of the present study will help the researchers to identify the research gap based on the present status of work done and to improve the performance of the cross flow turbine further in the future. • Experimental investigations on the performance of cross flow turbine is reviewed. • Numerical investigations carried out by several researchers is presented. • Performance of the cross flow turbine with varying geometrical parameters is analyzed. • Research gap and the scope for future work are discussed. [ABSTRACT FROM AUTHOR]

Abstract Indonesia has a lot of civilization without electricity in remote areas. In order to fulfill the high demand of electricity, low cost and environmentally friendly power plants are required to reach remote areas. Micro-hydro power plants are proposed as a solution that could penetrate the limited accessibility for transport, technology, and cost. This paper covers a case study of optimization potential analysis of micro-hydro power plant (MHPP) in Subang. This study analyze the current technical specification of the MHPP in Subang in order to optimize the operation to reach the attached generator capacity with the condition of low head and low discharge of the river. Analysis of the existing MHPP proposes a redesign focused on the penstock pipe and turbine. According to the calculations, penstock pipe design has the minimum required diameter of 0.7 m in order to withstand the debit of 1.1 m3/s. Besides, in order to optimize the cross flow turbine performance with the debit of 1.1 m3/s, the existing turbine's radius should be redesigned to 0.71 m, with the existing turbine's blade length should be redesigned to 0.248 m. All of the redesigns proposed could increase the potential power generation up to 200% from the current condition. [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]