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— A better understanding of the flow field of the cross-flow turbine (CFT) will be useful in its design and operation. As far as is known, no comprehensive study carried out relating to the effect of Reynolds number to turbulent shear stress, shear wall, energy kinetic turbulent, dissipation rate and Reynolds stress, and the occurrence of vortices around the runners of the CFTs. This study was designed to investigate the flow field in the nozzle and runner of the CFT using computational fluid dynamics (CFD) method. CFD methods were chosen because they can visualize detailed flow patterns that other methods cannot. The setups used in the CFD method such as two-dimensional unsteady simulations, six degrees of freedom features, shear stress transport k-ω turbulent model, and pressure-based solver. Based on results, for the nozzle, the shape of the velocity profile shows that the highest momentum flux occurs at the end of the nozzle, near the runner. Distribution of shear wall was highest at the base and tip of the nozzle; it was lowest at the centre. The turbulent kinetic energy profile at the nozzle was proportional to the turbulent boundary layer profile, Reynolds stress and eddy viscosity. This indicated that nozzle shape affects the momentum flux; therefore, good nozzle geometry can transfer the maximum water energy into the blade. The nozzle’s optimum geometry can be achieved by discharge and direction, optimizing velocity magnitude. This minimizes energy loss due to friction between the stream, vortex and mass of wasted fluid. For the runner, the highest turbulent kinetic energy, dissipations rate and Reynolds stress were located at the runner. Not all the water’s energy converted into mechanic energy because the part of that energy was used in mixing between water and air. The establishment of lift force on the active blades was not caused by the flow field that crosses the upper part of the blade, but by the momentum of water that hit the lower part of the blade. A vortex formed due to separation of the flow from the blade significantly affected the runner’s performance rather than rotational flow (air phase) in the CFT. [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]

The small hydroelectric power plants (SHPP) are implemented in non-interconnected zones (NIZ) of developing countries. In which, the provision of electrical energy from the national interconnected system is not economically feasible. Therefore, in the literature, hydroelectric generation technologies have been implemented taking advantage of the energy available in the rivers. One of these technologies is the Michell-Banki type cross-flow turbines (MBT), which, despite having lower efficiencies than turbines such as Pelton and Francis, maintain their efficiency although fluctuations in site conditions. For this reason, different studies have been made to increase the efficiency of the MBT by making geometric modifications to both the nozzle and the rotor. The purpose of this study is to determine numerically the effect of the geometry of the blades that form the runner on the efficiency of Michell-Banki Turbine (MBT). For this, two (2) geometries were studied corresponding to a circular sector of a standard tubular profile and an airfoil NACA 6512 modified in curvature profile and chord length, according to the profile of the standard tubular blade. For this study, transient simulations for multiphase water-air flow were implemented using a k--ε turbulence model in the Ansys 2020R1® CFX software. The two (2) turbine models were configured to the same hydraulic conditions of head and volumetric flow corresponding to 0.5 m and 16.27 L/s, respectively. Variations in rotational speed were configured between 100 and 200 RPM with 20 RPM steps. It was found that using the modified 6512 hydrodynamic profile, at 140 RPM increased efficiency by 6 %, compared to the conventional tubular type blade geometry. [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]

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]

Electricity is one of the essential requirements for the economic development of a country. In Ethiopia, more than half of the total population does not have access to electric power. Micro-hydropower (MHP) is one of the most feasible renewable energy options for providing reliable electricity to rural areas. However, in low-income countries such as Ethiopia, the high price of a purpose-made turbine to generate electricity from MHP resources is difficult. This paper presents the feasibility study of a pump as a turbine (PAT) for MHP applications with and without impeller blade modification. The analysis was conducted in terms of initial investment cost, the net present value, payback periods, and the cost of energy. Decreasing blade thickness, blade tip rounding, adjusting blade inlet angle, and blade grooving, then comparing the result with PAT without modification and cross-flow turbine are the modification techniques considered in this research. Based on the projected system lifetime, the equivalent cost of power for the PAT and cross-flow turbines are 0.065 and 0.100 $/kWh respectively. The cross-flow turbine's payback period is 6.04 years, which is significantly longer than the PATs payback period of 3.42 years. From the entire study, it can be concluded that the MHP coupled with PAT provides a lower payback period and cheaper power production. Whereas, impeller blade modification has no significant advantage from the economic point of view. Generally, the impeller modification cost needs to be less than or equal to 25% of the initial cost of the PAT to use the less cost advantage of the PAT. [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]

A numerical and experimental study was carried out for validation of a previously proposed design criterion for a cross-flow turbine and a new semi-empirical formula linking inlet velocity to inlet pressure. An experimental test stand was designed to conduct a series of experiments and to measure the efficiency of the turbine designed based on the proposed criterion. The experimental efficiency was compared to that from numerical simulations performed using a RANS model with a shear stress transport (SST) turbulence closure. The proposed semi-empirical velocity formula was also validated against the numerical solutions for cross-flow turbines with different geometries and boundary conditions. The results confirmed the previous hydrodynamic analysis and thus can be employed in the design of the cross-flow turbines as well as for reducing the number of simulations needed to optimize the turbine geometry. [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]

Cross-flow turbine performance is sensitive to multiple dimensionless parameters, including the Reynolds number, blockage ratio, and Froude number, based on both turbine submergence depth and overall channel depth. Here, we experimentally isolate the effects of each parameter. Turbine performance and free surface deformation were characterized in a recirculating flume at a baseline operating condition. Then, each parameter was independently increased by approximately 30% from the baseline case while all others were held roughly constant. Turbine performance, quantified by the power coefficient, was most sensitive to an increase in Reynolds number, followed by the blockage ratio and submergence depth Froude number. Increasing the channel depth Froude number had a negligible effect on performance. In contrast, increasing the channel depth Froude number caused the largest change in free surface deformation, and increasing the Reynolds number had a negligible effect on free surface deformation relative to the baseline case. Turbine performance changes are caused by a combination of blade hydrodynamics and strut losses, both of which are affected differently by each dimensionless parameter. These results suggest that each dimensionless parameter describes different fluid dynamics and that all four parameters should be considered during experimental design. Notably, we observe that turbine performance is sensitive to the submergence depth Froude number, a parameter that has not been previously explored in the archival literature. • Some dimensionless parameters affect power output of a cross-flow current turbine. • Power increases with the blockage ratio and Reynolds/submergence Froude numbers. • The channel depth Froude number has a minimal effect on power. • Free surface deformation is affected by the blockage ratio and Froude numbers. • The power increase with Reynolds number does not affect free surface deformation. [ABSTRACT FROM AUTHOR]

In the last few decades, hydropower production has been moving toward a new paradigm of low and diffused power density production of energy with small and mini-hydro plants, which usually do not require significant water storage. In the case of nominal power lower than 20 kW and ultra-low head H (H < 5 m), Archimedes screw or Kaplan type turbines are usually chosen due to their efficiency, which is higher than 0.85. A new cross-flow type turbine called Ultra-low Power Recovery System (UL-PRS) is proposed and its geometry and design criteria are validated in a wide range of operating conditions through 2D numerical analysis computed using the ANSYS Fluent solver. The new proposed solution is much simpler than the previously mentioned competitors; its outlet flow has a horizontal direction and attains similar efficiency. The costs of the UL-PRS turbine are compared with the costs of one Kaplan and one cross-flow turbine (CFT) in the case study of the main water treatment plant of the city of Palermo in Italy. In this case, the UL-PRS efficiency is estimated using a URANS 3D numerical analysis computed with the CFX solver. [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]

This research aimed to increase the efficiency of a pico-hydropower plant with Banki type turbines by installing a guide vane system as the inlet water control. It was observed that the inlet angle of attack and the number of turbine blades had affected the efficiency of the pico-hydropower plant. Moreover, a computational fluid dynamics (CFD) simulation was conducted for validation by creating a guide vane with inlet angles of 5 to 30 degrees and a turbine with 15-40 blades. The turbulent model in the SOLIDWORKS Simulation was selected as the fluid dynamic model. The simulation results statistically showed that the inlet angle of attack had a greater influence on the torque than the number of blades, with Pvalues of 1.1893x10-7 and 0.3915, respectively. The efficiency investigation using a 25-blade turbine with inlet angles of attack of 5, 10, 15, 20, 24, and 30 degrees, showed that the turbine with the 24-degree inlet angle of attack had exhibited the highest system efficiency at 45.83%. This research focused on vertical axis Banki turbine, which has been designed for electrical generation in irrigational canal only. In the practical demonstration, a 3-kW electrical generator system was installed across the canal, and the system efficiency was also investigated. The results showed that the maximum system efficiency was at 48% with a 0.7 m system head and a flow rate of 0.4 m3/s. This represents results which were higher than predicted from the simulation at 45.83% and a greater performance than that of the generating system without a guide vane at 34.96%. [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]