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Low/zero-head cross-flow turbines (LZH-CFT) possess vast potential in the field of renewable energy technology. This research presents a modified design of a cross-flow turbine specifically engineered to harness the untapped hydro-kinetic energy from low/zero-head water resources. Unlike traditional hydro turbines, the LZH-CFT leverages a cross-flow configuration to utilize the water flows of natural streams, making it an ideal solution for flow channels with low/zero head. The design is modified through ANSYS simulations by varying the rotor’s blade angles (from 0 to 90°) and 60° angle is found optimum. The prototype model of modified design is prepared and tested, which represents 62.5% RPM efficiency and provides double power as compared to the typical cross-flow turbine.

Crisis electricity was a crucial issue in the rural area. Crossflow turbine (CFT) in pico in pico scale is the best option for electricity provider for rural areas. Due to its usefulness and development of computer technology, computational fluid dynamics method application for CFT study becomes increasingly frequent. This paper compiles the implementation of the computational fluid dynamic (CFD) approach for CFT on a pico scale. Based on the literature, the Renormalization Group (RNG) turbulence model is recommended to predict the flow field that occurs in CFT because its error is lower than others turbulence models, the RNG error of 3.08%, standard of 3.19%, and transitional SST of 3.10%. Furthermore, six-degrees of freedom (6-DoF) is recommended because it has an error of 3.1% than a moving mesh of 9.5% for the unsteady approach. Thus, based on the review, the RNG turbulence model and 6-DoF are recommended for the CFT on the pico scale.

Indonesia is an agrarian country that continuously produces water, so it has the potential to develop a hydroelectric power plant. Computational Fluid Dynamic (CFD) application could be used to be an economical, quick, and efficient approach to improve the engineering design and turbine performance. This research aimed to find the effect of guide vane opening variations and total blades on cross-flow turbine performance using CFD simulation. This research used experimental modelling method with ANSYS program for turbine design with 22, 24, and 26 turbine blades and guide vane opening variations of 12°, 16°, 20°, 24°, and 36°. The data were collected by reviewing the simulation results after the numerical calculation process. The results showed that the cross-flow turbine performance was improving along with the increasing guide vane opening. The optimum turbine performance (power and efficiency) was obtained at 24° opening of guide vane and 26 total blades, producing 868.53 W power with 75.16% efficiency.

This study looked at the effects of flow rates and guide vane angles on the performance of a cross flow turbine, which can be used to generate energy and hydraulic power with low head and low flow rates of water. A fluid dynamic analysis was performed on the cross-flow turbine with the aid of finite element techniques. The simulation was solved after validating the convergence of the provided model and its boundary conditions, with the outputs being the velocity profiles of the flow in the rotor and the pressure distribution on the rotor surface during its rotations. Experimental evaluation of the cross-flow turbine guide vane positions at a flow rate of 0.8, 0.6, and 0.5 m3/s was conducted, and it was discovered that a maximum turbine speed of 482 rpm and a generator speed of 1920 rpm were produced at the rotor shaft at a flow rate of 0.8 m3/s with a head of 25 m, and this data was validated by the results produced from the simulation. Doi: 10.28991/HIJ-2022-03-01-06 Full Text: PDF

Turbines are critical parts in hydropower facilities, and the cross-flow turbine is one of the widely applied turbine designs in small- and micro-hydro facilities. Cross-flow turbines are relatively simple, flexible and less expensive, compared to other conventional hydro-turbines. However, the power generation efficiency of cross-flow turbines is not yet well optimized compared to conventional hydro-turbines. In this article, a Computational Fluid Dynamics (CFD)-driven design optimization approach is applied to one of the critical parts of the turbine, the valve. The valve controls the fluid flow, as well as determines the velocity and pressure magnitudes of the fluid jet leaving the nozzle region in the turbine. The Non-Uniform Rational B-Spline (NURBS) function is employed to generate construction points for the valve profile curve. Control points from the function that are highly sensitive to the output power are selected as optimization parameters, leading to the generation of construction points. Metamodel-assisted and metaheuristic optimization tools are used in the optimization. Optimized turbine designs from both optimization methods outperformed the original design with regard to performance of the turbine. Moreover, the metamodel-assisted optimization approach reduced the computational cost, compared to its counterpart.

Experiments were performed with a large laboratory-scale high solidity cross-flow turbine to investigate Reynolds number effects on performance and wake characteristics and to establish scale thresholds for physical and numerical modeling of individual devices and arrays. It was demonstrated that the performance of the cross-flow turbine becomes essentially R e -independent at a Reynolds number based on the rotor diameter R e D ≈ 10 6 or an approximate average Reynolds number based on the blade chord length R e c ≈ 2 × 10 5 . A simple model that calculates the peak torque coefficient from static foil data and cross-flow turbine kinematics was shown to be a reasonable predictor for Reynolds number dependence of an actual cross-flow turbine operating under dynamic conditions. Mean velocity and turbulence measurements in the near-wake showed subtle differences over the range of R e investigated. However, when transport terms for the streamwise momentum and mean kinetic energy were calculated, a similar R e threshold was revealed. These results imply that physical model studies of cross-flow turbines should achieve R e D ∼ 10 6 to properly approximate both the performance and wake dynamics of full-scale devices and arrays.

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

In the electrical energy generation context in Colombia, the water resources represent the 64% of the potential generated according to UPME in the 2015 year; becoming into a solution to the growing energy demand and to the supply of energy in non-interconnected zones. The cross-flow turbines as Michell-Banki type, become an efficient and economically attractive choice. This paper shows the fluiddynamic performance of a laboratory’s model turbine under several operating conditions. The development of this analysis is supported by the results of experimental tests, uses the computational fluid dynamics as a tool for modelling, estimate, and analyse the turbine behaviour under different operating conditions, with ANSYS-Fluent software; the computational model considers the most important geometric aspects of the turbine and the opening percentage effect of the guide blade. The water flow through the rotor is approach through a turbulence model as κ – ε type. The numerical study results agree satisfactorily with the turbine performance observed in the laboratory.

This paper presents a parametric study of H-Darrieus turbines in cavitating conditions. The objective of this work is to assess the impact of cavitation on turbine performances for a wide variety of configurations and under various operating conditions. A better insight on the most “cavitation-friendly” turbine is provided by determining the optimal design parameters in terms of solidity, deployment depth, number of blades and blade pitch angle. Such design parameters are studied here and help to identify and analyse the inception and effects of cavitation. Two-dimensional URANS numerical simulations are carried out within Star-CCM+ at a Reynolds number of 107 based on the turbine diameter. The cavitating conditions simulated in this paper correspond to near-surface deployments at free-stream velocities ranging from 2 to 3 m/s. In a first phase, the solidity is varied from 0.1 to 0.7 while the tip-speed ratio is varied accordingly for optimal power coefficient. It is shown that a higher solidity turbine operating at a lower tip-speed ratio is beneficial in cavitating conditions due to the low effective velocity on the blades. The chord-to-radius ratio is varied in the second phase of this study. Turbines with 1, 3, 6 and 9 blades for a constant solidity of 0.6 are simulated and the results show that a larger chord-to-radius ratio is detrimental in cavitating conditions. Thus, the high curvature effects are to be avoided by using a larger number of blades for a given turbine solidity. The third and final phase of this study simulates turbines where the blade pitch angle was varied from −6° to +2° for a medium turbine solidity of 0.3. The small negative blade pitch angles of −2° and −4° show promising results where cavitation is greatly reduced, showing an improvement on power coefficient of 45 % for a blade pitch angle of −4° compared to the no blade pitch angle case at a cavitation number of 35. Overall, this paper concludes on the fact that the blade’s effective velocity and angle of attack are the key parameters controlling cavitation and that a combination of the studied design parameters should be considered to completely avoid cavitation inception or limit its detrimental effect on performance.

This experimental study is focused on quantifying the effect of trailing edge flexibility on the performance of a three straight bladed vertical axis wind turbine, with a chord-to-diameter ratio c/D=0.16at a moderately high Reynolds number (based on diameter) ReD=4⋅105. The blades consist of NACA-0015 profiles that are fixed with a pitch angle β=6∘toe-out, and allow interchangeable trailing edges in the last 17% of their chord length. The research presented here provides a proof of concept for the improved performance of vertical axis wind turbines, due to the effect of flexibility at the trailing edge of their blades. We show that blades with semi-flexible trailing edge, can extend the range of rotor operating regimes, leading to an increase of approximately 10% in the performance of the turbine. An excess of flexibility results in diminished efficiencies.

The cost effective design of tidal turbines requires a good estimation of the loading cycles and their extrema that are related to the unsteady fluctuation of the current velocity. Apart from the ambient turbulence, the main source of velocity fluctuation is the presence of surface waves. In the present study, we analyse the effect of waves propagating against the current on the performance and the loads of a twin vertical axis tidal turbine by an experimental approach at a 1/20 scale. Overall, the results show little or no effect of the waves on the average power and loads compared to the conditions with current only, but a significant impact on their standard deviation that rises linearly with the amplitude of the waves. The drag, lift, and pitching moment show extended ranges up to 7.5 times higher and extreme values exceedance by 60 to 100% with irregular waves compared to the conditions without waves. That load and power fluctuation increase is totally due to the presence of waves as the coherence function between the rotor torque or the loads and the velocity spectra exceed 0.5 on the whole wave frequency bandwidth. The results also reveal a rotational sampling of the waves by the rotors that had also been observed on horizontal axis turbines. From a structural design point of view, the authors recommend conducting tests in irregular wave conditions as both the load ranges and extreme values are 1.5 to 2 times higher than those encountered with regular waves of the same significant height and period.

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.

Both scientific and industrial communities have a growing interest in marine renewable energies. There is a wide variety of technologies in this domain, with different degrees of maturity. This study focuses on two models of a mast-free vertical axis Darrieus tidal turbine with the objective of characterizing the effect of vertical confinement, rotor configuration, and fluid–structure interactions on their performances in free-surface flows. The first model comprised four straight rigid blades maintained by circular flanges on both ends of the rotor and the second model is equipped with free-ended interchangeable blades attached to a single upper flange. Two configurations of the second model mounted with either rigid or flexible blades were used, first for comparison with the dual-flange turbine, then in order to address the effect of fluid–structure interactions on the turbine performances. While the single-flange models exhibit a significantly lower efficiency at all operating points, it is observed that the use of flexible blades tends to enhance turbine performances at low Reynolds numbers. The flow topology obtained from PIV measurement at selected operating points is discussed with respect to the performance of each turbine model in order to highlight the role of the dynamic stall and blade–vortex interactions.

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.

Kedung Kayang waterfall is located on the border of Magelang and Boyolali regency of Central Java. The waterfall is 38 meters high, so it has the potential to be used as a micro hydro power plant (MHP). In designing the MHP, it requires some studies including hydrology, civil, mechanical, and electrical. The purpose of this research is to predict the water discharge, determine the potential of hydro power, selection of MHP sites, design of hydro turbine and electric generator. This research uses Penman Modification method to calculate evapotranspiration, Mock method to calculate water discharge, geographical mapping for MHP sites selection and cross-flow turbine design calculation. This paper presents the results of MHP design consist of MHP capacity, selection of MHP sites, penstock design, cross-flow turbine design and electric generator selection. The result showed that dependable water discharge is 0.143 m3 / sec, effective head is 19.5 meters, hydro potential is 27.33 kW, and electric power that can be produced is 18 kW, length and diameter penstock are 81,74 m and 26,77 m, hydro turbine used cross flow type with outer diameter of the runner is 17,17 cm, inner diameter is 11,45 cm and width is 59,16 cm. MHP site is located in Klakah village, Selo Sub-district, Boyolali District.

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.

Cross-flow hydrokinetic turbines have sparked interest among fluid dynamicists for their potential for power enhancement in paired configuration. Following the first part of a laboratory-scaled turbine wake measurement project, this second part presents a monoscopic particle image velocimetry measurement of the near-wake of two cross-flow hydrokinetic turbines in six different counter-rotating configurations. The turbines operated in a small water flume at an average diameter-based Reynolds number of 2×104 with the incoming streamwise velocity of 0.316 m/s. The six configurations included two turbine separation distances, two turbine phase angles differences, and two different relative incoming flow angles. Similar to the observation of the single turbine configurations in part I, a correlation between flow field structures and the corresponding power output was observed. Effects of each parameter of the counter-rotating configurations are further discussed, which suggest guidelines for setting up multiple devices in a power farm. This article is accompanied by all full numeric data sets and videos of the results.

An open-source 2D Reynolds-averaged Navier–Stokes (RANS) simulation model was presented and applied for a laboratory-scaled cross-flow hydrokinetic turbine and a twin turbine system in counter-rotating configurations. The computational fluid dynamics (CFD) model was compared with previously published experimental results and then used to study the turbine power output and relevant flow fields at four blockage ratios. The dynamic stall effect and related leading edge vortex (LEV) structures were observed, discussed, and correlated with the power output. The results provided insights into the blockage effect from a different perspective: The physics behind the production and maintenance of lift on the turbine blade at different blockage ratios. The model was then applied to counter-rotating configurations of the turbines and similar analyses of the torque production and maintenance were conducted. Depending on the direction of movement of the other turbine, the blade of interest could either produce higher torque or create more energy loss. For both of the scenarios where a blade interacted with the channel wall or another blade, the key behind torque enhancement was forcing the flow through its suction side and manipulating the LEV.

Recent developments in marine hydrokinetic (MHK) technology have put the cross-flow (often vertical-axis) turbines at the forefront. MHK devices offer alternative solutions for clean marine energy generation as a replacement for traditional hydraulic turbines such as the Francis, Kaplan, and Pelton. Following previous power measurements of laboratory-scaled cross-flow hydrokinetic turbines in different configurations, this article presents studies of the water flow field immediately behind the turbines. Two independent turbines, which operated at an average diameter-based Reynolds number of approximately 0.2×105, were driven by a stepper motor at various speeds in a closed circuit water tunnel with a constant freestream velocity of 0.316 m/s. The wakes produced by the three NACA0012 blades of each turbine were recorded with a monoscopic particle image velocimetry technique and analyzed. The flow structures with velocity, vorticity, and kinetic energy fields were correlated with the turbine power production and are discussed herein. Each flow field was decomposed into the time averaged, periodic, and random components for all the cases. The results indicate the key to refining the existed turbine design for enhancement of its power production and serve as a baseline for future comparison with twin turbines in counter-rotating configurations.

Oscillating hydrofoils were installed in a water tunnel as a surrogate model for a hydrokinetic cross-flow tidal turbine, enabling the study of the effect of flexible blades on the performance of those devices with high ecological potential. The study focuses on a single tip-speed ratio (equal to 2), the key non-dimensional parameter describing the operating point, and solidity (equal to 1.5), quantifying the robustness of the turbine shape. Both parameters are standard values for cross-flow tidal turbines. Those lead to highly dynamic characteristics in the flow field dominated by dynamic stall. The flow field is investigated at the blade level using high-speed particle image velocimetry measurements. Strong fluid–structure interactions lead to significant structural deformations and highly modified flow fields. The flexibility of the blades is shown to significantly reduce the duration of the periodic stall regime; this observation is achieved through systematic comparison of the flow field, with a quantitative evaluation of the degree of chaotic changes in the wake. In this manner, the study provides insights into the mechanisms of the passive flow control achieved through blade flexibility in cross-flow turbines.

With the aim of finding efficient solutions for cross flow turbine (CFT) bi-directional diffusers able to harvest non perfectly rectilinear tidal currents, a 2D CFD analysis of ducted CFTs was carried out with focus on the effects of diffuser shape and yaw angle. The HARVEST hydrofoil shaped diffuser, equipped with a pair of counter-rotating turbines, and a bi-directional symmetrical diffuser were compared in terms of coefficient of power (CP), torque ripple, overall thrust on diffuser and wake characteristics. Slightly better CP were predicted for the symmetrical diffuser, due to the convergent walls that address the flow towards the blade with a greater attack angle during early and late upwind and to the viscous interactions between the turbine wakes and strong vortices shed by the diffuser. A CP’s extraordinary improving resulted when yaw increased up to 22.5° for the hydrofoil shaped and up to 30° for the symmetrical diffuser. Similar behaviour in yawed flows also occurred in case of a ducted single rotor, demonstrating that it is a characteristic of CFTs. The insertion of a straight throat in the diffuser design proved to be an effective way to mitigate torque ripple, but a CP loss is expected.

This article proposes an experimental apparatus design to measure the power of a cross-flow marine hydrokinetic turbine system operating in a laboratory water tunnel. Data, from one Hall sensor output signal, was processed to capture the three types of torque exerted on the turbines: mechanical loss, brake, and hydrodynamic torque. The method was then applied to compare the power of a twin turbine system in different counter-rotating configurations. Controlled by a hysteresis brake, the tip-speed-ratio was varied in a constant freestream velocity of 0.316 m/s. While the braking torque was independent of the speed, the mechanical loss was found to depend on the system rotational speed and the amount of mass mounted on the mechanical support. In a counter-rotating configuration, the turbines were synchronized through a pair of spur gears and timing pulleys. Operating at the average chord based Reynolds number of 8000, each turbine had three NACA0012 blades mounted at 15∘ pitch angle. The power coefficient results of 8 turbine configurations showed the tendency of power enhancement of counter-rotating configurations due to blade interaction and increase in blockage ratio. Comparison of the results suggested direct application in a river flow scenario and manipulation of the blade interaction for optimal power production.

Recently, small hydropower attracts attention because of its clean, renewable and abundant energy resources to develop. Therefore, a cross-flow hydraulic turbine is proposed for small hydropower in this study because the turbine has relatively simple structure and high possibility of applying to small hydropower. The purpose of this study is to investigate the effect of the turbine's structural configuration on the performance and internal flow characteristics of the cross-flow turbine model using CFD analysis. The results show that nozzle shape, runner blade angle and runner blade number are closely related to the performance and internal flow of the turbine. Moreover, air layer in the turbine runner plays very important roles of improving the turbine performance.

In hydropower, the exploitation of small power sources requires the use of small turbines that combine efficiency and economy. Banki-Michell turbines represent a possible choice for their simplicity and for their good efficiency under variable load conditions. Several experimental and numerical tests have already been designed for examining the best geometry and optimal design of cross-flow type machines, but a theoretical framework for a sequential design of the turbine parameters, taking full advantage of recently expanded computational capabilities, is still missing. To this aim, after a review of the available criteria for Banki-Michell parameter design, a novel two-step procedure is described. In the first step, the initial and final blade angles, the outer impeller diameter and the shape of the nozzle are selected using a simple hydrodynamic analysis, based on a very strong simplification of reality. In the second step, the inner diameter, as well as the number of blades and their shape, are selected by testing single options using computational fluid dynamics (CFD) simulations, starting from the suggested literature values. Good efficiency is attained not only for the design discharge, but also for a large range of variability around the design value.

The presented article brings general overview of CFD analysis of two cross-flow turbine types (a classical impulse turbine and a reaction turbine). The author focuses his attention mainly on the discussion of differences in flow patterns in the outflow section of these turbines, because this element exerts significant impact on performance properties of the turbine. The article presents a comparison of computations and experimental results of the cross-flow turbine manufactured by IMP PAN. The analysis was performed by means of a computer program Fluent 5.0TM for a twodimensional example.

Transients in hydropower plants can result in serious disturbances in a plant operation and damage of mechanical and civil components. The best way to prevent such adverse outcomes is to conduct a transient-state analysis using a mathematical model of the hydropower plant system. Based on the collected data on 270 hydropower plants with cross-flow turbines, regression equations were derived that relate a cross-flow turbine specific speed, rated speed, runner diameter and runner width to the rated turbine head and discharge. The obtained equations were used to estimate the turbine performance characteristics using available unit hill charts of three different cross-flow turbines. Finally, the estimated performance characteristics were used to form the boundary condition ‘cross-flow turbine’ within the unsteady 1D mathematical model. The model was validated through case studies by comparing calculated and measured changes in the turbine speed and inlet pressure, induced by sudden load rejection. The difference between the calculated and measured peak pressures was up to 5% during the most critical period, that is, from the moment of load rejection up to the guide vanes closure. In the case of turbine speed, the difference between the peak values was less than 10% in the same period.

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.

Tidal turbines are one source of marine renewable energy but development of tidal power is hampered by uncertainties in fish-turbine interaction impacts. Current knowledge gaps exist in efforts to quantify risks, as empirical data and modeling studies have characterized components of fish approach and interaction with turbines, but a comprehensive model that quantifies conditional occurrence probabilities of fish approaching and then interacting with a turbine in sequential steps is lacking. We combined empirical acoustic density measurements of Pacific herring (Clupea pallasii) and when data limited, published probabilities in an impact probability model that includes approach, entrainment, interactions, and avoidance of fish with axial or cross-flow tidal turbines. Interaction impacts include fish collisions with stationary turbine components, blade strikes by rotating blades, and/or a collision followed by a blade strike. Impact probabilities for collision followed by a blade strike were lowest with estimates ranging from 0.0000242 to 0.0678, and highest for blade strike ranging from 0.000261 to 0.40. Maximum probabilities occurred for a cross-flow turbine at night with no active or passive avoidance. Estimates were lowest when probabilities were conditional on sequential events, and when active and passive avoidance was included for an axial-flow turbine during the day. As expected, conditional probabilities were typically lower than analogous independent events and literature values. Estimating impact probabilities for Pacific herring in Admiralty Inlet, Washington, United States for two device types illustrates utilization of existing data and simultaneously identifies data gaps needed to fully calculate empirical-based probabilities for any site-species combination.

A good understanding of aerodynamic loading is essential in the design of vertical-axis wind turbines (VAWTs) to properly capture design loads and to estimate the power production. This paper presents a comprehensive aerodynamic design study for a 5 MW Darrieus offshore VAWT in the context of multi-megawatt floating VAWTs. This study systematically analyzes the effect of different, important design variables including the number of blades, aspect ratio and blade tapering in a comprehensive load analysis of both the parked and operating aerodynamic loads including turbine power performance analysis. The number of blades is studied for two- and three-bladed turbines, aspect ratio is defined as ratio of rotor height and rotor diameter and studied for values from 0.5 to 1.5, and blade tapering is applied by means of adding solidity to the blades towards blade root ends, which affects aerodynamic and structural performance. Analyses were carried out using a three-dimensional vortex model named CACTUS (Code for Axial and Cross-flow TUrbine Simulation) to evaluate both instantaneous azimuthal parameters as well as integral parameters, such as loads (thrust force, lateral force and torque loading) and power. Parked loading is a major concern for VAWTs; thus, this work presents a broad evaluation of parked loads for the design variables noted above. This study also illustrates that during the operation of a turbine, lateral loads are on par with thrust loads, which will significantly affect the structural sizing of rotor and platform and mooring components.

The maximum exploitable potential for low head hydroelectric sites (gross head≤10 m) in Northern Ireland (NI) was determined as 12.07 MW using a simple payback analysis for 304 potential sites investigated to derive a classification scheme in terms of economic viability. A techno-economic analysis with validated numerical models from previous research estimated the capital investment required for the development of a hydroelectric plant, using the low head Michell-Banki cross flow turbine, for the 304 sites investigated. The number of potentially viable sites in NI for low head hydro ranged from 198 to 286 with an estimated installed capacity ranging from 11.95 to 12.05 MW. Sites with a limited installed capacity were not economically viable unless increased government support in the form of longer term (25–50 years) low interest loans as well as the current (Renewables Obligations Certificates) Renewables Obligation Certificates scheme is provided and sustained.

The Model of Fluid Dynamics Computation (CFD) aims to obtain cross-tubine flow in microhydro tubes. The parameters used to determine the cross flow turbine power are the blade angle, the number of cross runner blades and the head tube as the production house. Computational Fluid Dynamics (CFD) is software that can load integral and partial equations into discrete algebraic equations (addition, multiplication, multiplication and division) that can be used with the help of computers to find solutions for sources and times. In the era of technology, the development of the Computational Fluid Dynamics (CFD) program is very fast making this method a trend in various fields of industry that utilizes a comparison of pure experimental data and pure theory. The study of turbine cross flow power on microhydro tubes shows 1213 Watt power on the parameters of blade number 16, blade angle of 150 and 200 at head 4 meters.

Cross-flow turbines have a number of potential advantages for hydrokinetic energy applications. Two novel control schemes for improving cross-flow turbine energy conversion are introduced and demonstrated through scale experiments. The first aims to alter the local flow conditions on the blades through varying blade kinematics as a function of rotational position, thus increasing beneficial fluid forcing. An established method accomplishes this by oscillating the mounting angle of the blade. Instead we proposed to vary the angular velocity of the blade as a function of azimuthal position. Optimizing this controller resulted in a 59% increase in turbine performance over standard controllers. The second control scheme operates an array of two turbines in a coordinated manner to take advantage of periodic wake structures. For a range of relative turbine positions, a parent controller maintains a constant blade position difference between turbines with the same angular velocity. For select positions, the array efficiency is shown to be greater than that of a single turbine. At the optimal position, coordinated control results in a 4% increase in array performance over uncoordinated operation. Finally, intracycle angular velocity and coordinated control schema are combined.

The purpose of this experiment is to know the influence of a single guide vane position and angle to the performance of a cross-flow wind turbine. The cross-flow wind turbine was positioned at the discharge outlet of a cooling tower model to harness the discharged wind for electricity generation. A guide vane was used to enhance the rotational speed of the turbines for power augmentation. Various position and angle of attack of the guide vane were tested in this experiment. To avoid negative impact on the performance of the cooling tower fan and to optimize the wind turbine performance, the turbine position on the discharge wind stream was also studied. The result showed that cross-flow wind turbine with a guide vane attached at the right position had a higher coefficient of power than cross flow turbine without guide vane. A crossflow wind turbine with the guide vane at the position of 150 mm from the center and 30° angles had the highest coefficient of power of 0.49. Comparing to the wind turbine without guide vane, the coefficient of power of the cross-flow wind turbine was increased about 84.3%.

This paper describes the present status of the art on air turbines, which could be used for wave energy conversion. The air turbines included in the paper are as follows: Wells type turbines, impulse turbines, radial turbines, cross-flow turbine, and Savonius turbine. The overall performances of the turbines under irregular wave conditions, which typically occur in the sea, have been compared by numerical simulation and sea trial. As a result, under irregular wave conditions it is found that the running and starting characteristics of the impulse type turbines could be superior to those of the Wells turbine. Moreover, as the current challenge on turbine technology, the authors explain a twin-impulse turbine topology for wave energy conversion.

The paper refers to the numerical analysis of the internal flow in a hydraulic cross-flow turbine type Banki. A 3D-CFD steady state flow simulation has been performed using ANSYS CFX codes. The simulation includes nozzle, runner, shaft, and casing. The turbine has a specific speed of 63 (metric units), an outside runner diameter of 294 mm. Simulations were carried out using a water-air free surface model and k-ε turbulence model. The objectives of this study were to analyze the velocity and pressure fields of the cross-flow within the runner and to characterize its performance for different runner speeds. Absolute flow velocity angles are obtained at runner entrance for simulations with and without the runner. Flow recirculation in the runner interblade passages and shocks of the internal cross-flow cause considerable hydraulic losses by which the efficiency of the turbine decreases significantly. The CFD simulations results were compared with experimental data and were consistent with global performance parameters.