Low Cut-in Speed Research Articles

Techno-Economic Analysis of Combined Production of Wind Energy and Green Hydrogen on the Northern Coast of Mauritania

Green hydrogen is becoming increasingly popular, with academics, institutions, and governments concentrating on its development, efficiency improvement, and cost reduction. The objective of the Ministry of Petroleum, Mines, and Energy is to achieve a 35% proportion of renewable energy in the overall energy composition by the year 2030, followed by a 50% commitment by 2050. This goal will be achieved through the implementation of feed-in tariffs and the integration of independent power generators. The present study focused on the economic feasibility of green hydrogen and its production process utilizing renewable energy resources on the northern coast of Mauritania. The current investigation also explored the wind potential along the northern coast of Mauritania, spanning over 600 km between Nouakchott and Nouadhibou. Wind data from masts, Lidar stations, and satellites at 10 and 80 m heights from 2022 to 2023 were used to assess wind characteristics and evaluate five turbine types for local conditions. A comprehensive techno-economic analysis was carried out at five specific sites, encompassing the measures of levelized cost of electricity (LCOE) and levelized cost of green hydrogen (LCOGH), as well as sensitivity analysis and economic performance indicators. The results showed an annual average wind speed of 7.6 m/s in Nouakchott to 9.8 m/s in Nouadhibou at 80 m. The GOLDWIND 3.0 MW model showed the highest capacity factor of 50.81% due to its low cut-in speed of 2.5 m/s and its rated wind speed of 10.5 to 11 m/s. The NORDEX 4 MW model forecasted an annual production of 21.97 GWh in Nouadhibou and 19.23 GWh in Boulanoir, with the LCOE ranging from USD 5.69 to 6.51 cents/kWh, below the local electricity tariff, and an LCOGH of USD 1.85 to 2.11 US/kg H2. Multiple economic indicators confirmed the feasibility of wind energy and green hydrogen projects in assessed sites. These results boosted the confidence of the techno-economic model, highlighting the resilience of future investments in these sustainable energy infrastructures. Mauritania’s north coast has potential for wind energy, aiding green hydrogen production for energy goals.

Low-Wind-Speed Galloping Wind Energy Harvester Based on a W-Shaped Bluff Body

Galloping-based piezoelectric energy harvesting systems are being used to supply renewable electricity for low-power wireless sensor network nodes. In this paper, a W-shaped bluff body is proposed as the core component of a piezoelectric wind energy harvester. Experiments and simulations have shown that the W-shaped bluff body can improve harvesting efficiency at low wind speeds. For the W-shaped structure, the finite element simulation results indicate that the structure can help improve the aerodynamic performance to obtain high aerodynamic force. The experimental results demonstrate that compared with the traditional bluff bodies, the piezoelectric wind energy harvester with the W-shaped bluff body (WEHW) can generate higher output voltages and has a lower cut-in speed. When the length L is 30 mm and the rear groove angle β is 30°, the W-shaped structure can induce the best harvesting performance. When an external load resistance of 820 KΩ is connected and the wind speed is 5 m/s, the WEHW generates an average output power of 0.28 mW.

Assessment of the wind energy potential and economic viability of selected sites along Nigeria’s coastal and offshore locations

Wind energy is a promising sector in the power generation industry because it is renewable and globally available. In this research work, the wind energy potential and the economic viability of using wind turbines to generate electricity in some selected sites along Nigeria’s coastline and offshore locations were evaluated. Using the statistical two-parameter Weibull probability density function method, wind speed data retrieved from an indigenous oceanography company and global information system (GIS) were analyzed for wind energy harvest. The energy output, unit cost of electricity generated by three commercially available wind turbine models (3 MW, 4 MW, and 6 MW), net present value (NPV), and payback period were evaluated. Levelized cost of electricity (LCOE) sensitivity to the discount rate, foundation cost, and turbine lifespan were also examined. The findings from the study showed that the offshore sites have four times greater wind power potential than the coastal sites. The offshore sites can be categorized as “class IIIb” wind sites, making the locations suitable for wind energy harvest. The techno-economic analysis showed that the net gains from investing in a 60-MW wind farm in the region can be as high as $62,000,000.00, while the project payback time can be as low as 5.74 years. Two of the offshore sites are recommended for the development of an offshore wind farm in the country because of their relatively low LCOE (0.04 $/kWh), higher NPV, and lower investment payback time. The Vesta-117 model wind turbine is the most suitable wind turbine system and recommended for use in the region because of its low cut-in speed (3 m/s). Sensitivity analysis showed that the LCOE of offshore-01 was reduced by 31% when the lifespan of the V117 turbine was increased from 20 to 25 years. The results also showed that reductions in the discount rate and foundation cost positively affect the LCOE.

An investigation of a 3D printed micro-wind turbine for residential power production

The wind energy sector is rapidly growing and has become one of the most important sources of renewable power production. New technologies are being developed to increase energy production. This study focuses on developing and evaluating a 3-D printed micro-wind turbine system for residential electricity production. The effectiveness of using Poly Lactic Acid material for model production was assessed using the SolidWorks environment. Then, three–dimensional CFD model was developed to simulate a micro-wind turbine. The CFD model was validated in good agreement against scale physical model experiments performed in a wind tunnel. The results demonstrated that the 5-blade micro-wind turbine design was the most effective under the tested conditions, with a low cut-in speed and the ability to operate under torque up to 70 N.m. Finally, the currently available manufacturing processes for micro-wind turbines have been evaluated. Future work should evaluate the performance of the MWT system under realistic conditions in a site test to determine energy production and total efficiency

Effect of Stator Blades on the Startup Dynamics of a Vertical Axis Wind Turbine

Vertical Axis Wind Turbines (VAWTs) are omni-directional, low-cost, low-efficiency wind power extractors. A conventional drag-based VAWT consists of multiple thin rotor blades with a typical peak Tip Speed Ratio (λ) of < 1. Their lower cut-in speed and maintenance cost make them ideal for power generation in urban environments. Numerous studies have been carried out analysing steady operation of VAWTs and quantifying their performance characteristics, however, minimal attention has been paid to their start-up dynamics. There are a few recent studies in which start-up dynamics of lift-based VAWTs have been analysed but such studies for drag-based VAWTs are severely limited. In this study, start-up dynamics of a conventional multi-blade drag-based VAWT have been numerically investigated using a time-dependant Computational Fluid Dynamics (CFD) solver. In order to enhance the start-up characteristics of the drag-based VAWT, a stator has been integrated in the design assembly. The numerical results obtained in this study indicate that an appropriately designed stator can significantly enhance the start-up of a VAWT by directing the flow towards the rotor blades, leading to higher rotational velocity (ω) and λ. With the addition of a stator, the flow fields downstream the VAWT becomes more uniform.

Wind speed Weibull distribution and wind energy potential of Chandpur, Bangladesh

Weibull distribution goes particularly well with wind speed data and is necessary to assess wind energy harnessing potential at a site. For the best estimation of the statistical distribution parameters at Chandpur (23.21116° N; 90.64237° E), located at the southern part of Bangladesh, six models: graphical method, method of moments, power density method, Justus method, Lysen method and maximum likelihood method have been analyzed for 18.8 m, 40.2 m and 59.9 m above ground level (AGL) using measured wind speed data for 2014-2017. Out of the six models, Justus method has showed the best result for estimation of Weibull parameters at all heights AGL with average RMSE of 0.0082 and R2 of 0.9650. Further more to evaluate the wind energy potential at modern wind turbine hub height of 100 m, firstly the wind shear exponent at the site (the average value is 0.37 considering the 10 m elevation of the site above sea level) is estimated from the wind data of 3 heights; secondly average wind speed (4.88 m/s), wind power density (108.8 Wm-2), Weibull distribution parameters (shape factor 2.29 and scale factor 5.33 m/s) and wind turbine power curve related wind speeds (cut in 2.28 m/s, rated 9.33 m/s and cut out 21.03 m/s)have been extrapolated at the hub height. The average wind speed and wind power density values show that the class of the site is 1 in the worldwide accepted wind power classification, based on long term practical wind farm installation experiences; the low cut in speed (<3 m/s) shows that suitable wind turbines for the site are commercially unavailable for the site and turbines with 3 m/s cut in speed have average annual capacity factor of 16.62 %, less than the commercially viable capacity factor >25 %. The wind power class (< class 3) and capacity factor (<25 %) strictly reveals that Chandpur is not suitable for wind energy exploration in near future until a high technical improvement of wind turbines and reduction of relevant costs. DUJASE Vol. 6 (2) 99-108, 2021 (July)

Toward a high performance and strong resilience wind energy harvester assembly utilizing flow-induced vibration: Role of hysteresis

Wind energy harvester utilizing flow-induced vibration (FIV-WEH) has attracted much attention because of its ability to capture low-speed wind energy. This study is motivated to design a reliable FIV-WEH assembly in a wind farm, and to understand the altered environmental flow and disturbed output performance through large-eddy simulations and wind tunnel experiments, for the sake of harnessing fluctuating near-ground wind energy efficiently. The results demonstrates that the proposed eco-friendly FIV-WEH assembly has less impact on the surroundings due to the fast recovery of turbulent wake. Moreover, it is equipped with remarkable hysteresis caused by the delay of wake transition from 2P to C mode, which can enhance the output power, effective wind band, and more importantly, resilience. The resilience guarantees that the FIV-WEH assembly can harvest the fluctuating wind resources optimally even under strong turbulence intensity. Specifically, compact FIV-WEH assembly (l ≤ 1.5, where l is dimensionless streamwise span) based on extended-body regime has a low cut-in speed (3 m/s), showing great potential to harvest breeze energy in a near-ground residential environment. Loose FIV-WEH assembly (1.5 < l < 5) based on reattachment regime has a large cut-in speed (9 m/s) and low span-sensitivity, which can be flexibly adjusted to extract the wind energy in spacious wind-abundant areas. Finally, two strategies developed by modifying surfaces of FIV-WEH assembly can further enhance the resilience and conversion efficiency by approximately 200%.

Low-speed flutter of artificial stalk-leaf and its application in wind energy harvesting

Developing wind energy harvester (WEH) by mimicking the leaf flutter may provide an innovative way for increasing the power efficiency and decreasing the cut-in speed. The low-speed flutter mechanism of the stalk-leaf system is investigated through introducing a frictionless hinge into the stalk-leaf finite element model. The aeroelastic system is established by the usage of doublet-lattice aerodynamics and the spline interpolation between structural motion and flow downwash. The critical flutter speed and frequency are analyzed via V-g method. The evolution of damping and frequency with wind speed which various from static air to Beaufort level 5 are simulated. The influence of inclined angle of the stalk on the flutter characteristics is studied. The stainless-steel artificial stalk-leaf systems with inclined angles of 0°, 15°, 30°, 45°, 60°, 75°, and 90° are fabricated and tested in wind tunnel. The wind energy harvesting performance is also measured by attaching macro-fiber composite patches on root of the stalk. It is found that the 30° stalk-leaf WEH has the lowest critical flutter speed, while the energy harvesting output (voltage and power) increases slowly with the increase of the wind speed. On the contrary, although the 90° stalk-leaf (vertical stalk) WEH has the steepest velocity-voltage and velocity-power curve, it also has the highest cut-in speed. In the preliminary tests, the 30° stalk-leaf WEH outputs steady power density of 47.46 μW cm−3 with stable oscillating frequency of 6.6 Hz at 11 m s−1 wind, while the 90° stalk-leaf WEH outputs power density of 92.88 μW cm−3 with oscillating frequency of 7.2 Hz at the same wind speed. The stalk-leaf design presents a possible way to balance the performance between the high efficiency and the low cut-in speed for the WEHs.

Wind energy resource assessment for Mukdahan, Thailand

ABSTRACT The generation of electricity from wind energy can reduce the fossil sources imported and carbon dioxide emissions. The wind is free, clean, and green energy. This study aims to present a wind energy assessment for Mukdahan site of Thailand. The wind speed at heights of 60, 90, and 120 m above ground level was measured from January 1st, 2012 to December 31st, 2017. The annual mean wind speeds were 3.59, 4.02, and 4.51 m/s at 60, 90, and 120 m AGL, respectively. The majority of wind directions were contributed by the monsoon for this region. The Wind Atlas Analysis and Application Program (WAsP) was used to predict the Annual Energy Production and Capacity Factor for five selected wind turbines in a capacity range of 0.85 − 3.30 MW. Moreover, the high-resolution wind resource map also indicated the high potential for wind around the site. The low cut-in speed and high hub-height wind turbines such as VestasV110-2.0 MW and V126-3.3 MW can produce higher energy output, capacity factor and better cost of energy, especially when the wind turbine site is located on the ridges and peaks of hills around the site. The best cost of energy was 0.030 USD/kWh, which was observed for the V110 wind turbine and the second best was 0.041 USD/kWh for the V126 wind turbine, especially when considering placement on the peak of a hill. The important data from this study can be developed for wind farm project installation and suitable wind turbine design for the whole local region.

Wind Energy Potential in Gaza Strip-Palestine state

In this study, wind speed and direction data provided by Meteoblue AG-Switzerland as hourly time-series for 16 years from 2000 to 2015 for selected three cities in Gaza Strip, are used directly to evaluate the wind energy in the three selected sites which are geographically presenting the entire Strip. Jabalia is located in the North of Gaza Strip, Deir-albalah in the Middle and Rafah in the South. The wind rose diagrams have been depicted by using WRPLOT view 7.0.0 (wind rose plots for meteorological data from Lake Environmental, 2011). The statistical analysis of the data shows that; Rafah city is the first candidate to establish a wind farm in the entire Palestinian territory. The reason that, Rafah has the highest wind energy potential than the other sites. The second reason is that Rafah is located on the border crossing to Egypt, which facilitates the transfer of machinery, experts, and reduces transport and communication expanses. In addition to low population density, which increases the economic feasibility of utilizing wind energy at this location for remote area applications. The analysis has been done for a large types of wind turbines types. Gamesa G128-4.5 WT, which is manufactured for classes I and II wind speeds with low cut-in speed, was selected for our project. The estimated annual energy is 15,962 MWh/turbine, with an average utility factor of 40.4%; to cover the shortage of 200 MW we need to 110 WTs. The required area for the wind farm is estimated to be 43 km2.

Design and development of sail type wind turbine with solar panel

The main drivers of economic development of any society very often correlate with the access and use of energy. In fact, proper utilization of the resource requires technology. The industry needs green energy technology for sustainable development. Energy demands can be met by renewable energy sources, as fossil fuels getting depleted day by day. Solar, biomass, geothermal, wind and water energy can be used as the best alternate sources. Wind turbines are capable of extracting power form wind regardless of the direction of flow in both day and night. Solar photo voltaic cells can tap radiation from sun and can be converted in to electrical energy. Hybriding the systems has proved to be beneficial in terms of supplying load demand under varying weather conditions, which in turn make us to use these systems for power generation and overall costs for self-powered system may be reduced drastically, High reliability without backup power source combination is the advantage of this process. In this work also we would like to combine solar PVs and vertical axis wind turbines (VAWT) that can extract electrical energy. The advantages of vertical axis turbines has much better self- starting characters and better conversion efficiency at lower flaw speed. In this we used savonious type vertical axis turbine that produce higher torque and have lower cut in speed. This paper presents the urban Eco- Greenery hybrid wind- solar power generation by using VAWT turbine and solar tracking.

Design and construction of Savonius rotor

Renewable energy sources have been researched for more than a century now. Wind energy; which is often characterized as an unreliable source of energy, is not unreliable if placed at places with smooth wind currents. Savonius rotor as Vertical Axis Wind Turbine (VAWT) can be used as a standalone power generation device because of its low cost, low cut-in speed and the fact that it can accept wind from any direction. S-Rotors when compared to other types of rotors have a lower Power Coefficient but factors like Overlap ratio, Aspect Ratio, Number of Blades and Blade shapes can affect its efficiency. This paper discusses the Design and construction of a Savonius wind turbine by studying how the factors above influence the rotor’s performance. Finally, a Single-stage, Two blade conventional Savonius rotor with an Overlap Ratio of 0.1 and Aspect Ratio of 3.3 has been constructed and discussed below. Studies for choosing the best material have also been conducted and PolyVinyl Chloride (PVC) has been selected to prepare the blades from. According to the study conducted, the voltage output recorded at 5.4 m/s wind speed was 19.1 Volts.

Exploring the suitability of MERRA-2 reanalysis data for wind energy estimation, analysis of wind characteristics and energy potential assessment for selected sites in Pakistan

In the first part of this study, correlation between MERRA-2 reanalysis wind data and ground data is assessed for 12 selected locations. The correlation coefficient ranges from 0.17 to 0.75 among the sites. Sites with higher average wind speeds show comparatively stronger correlation. Besides, site specific factors are also investigated. In the second part, wind energy potential at same 12 locations is evaluated using high frequency (10-min interval) ground observed data. The diurnal, monthly and annual means for the sites are calculated and wind speed variance is observed utilizing wind data at six altitude levels (10m, 20m, 40m, 50m, 60m and 80m). The data is fitted to the Weibull distribution. Most probable wind speeds, wind speeds carrying maximum energy and wind power densities for all the locations are calculated for 50m and 80m height wind data. Significant variation of wind power density is observed along the height. A low cut-in speed wind turbine is selected, and annual energy production and capacity factors are estimated. Four locations with high wind power densities, namely Sujawal (355.6 W/m2), Sanghar (312.9 W/m2), Tando Ghulam Ali (288.2 W/m2) and Umerkot (252.8 W/m2) showed good potential to add wind share to global energy mix.

Effect of blade number and angle on the characteristics of the savonius type wind turbine

The savonius type vertical axis wind turbine can be operated in all wind directions, is low cut in speed and high in torque. Therefore, it is a potential source of energy in low wind areas. This research aimed to compare the performance of H-Savonius vertical axis wind turbine using blades numbers and blades angle. The turbine containing the blades numbers 4, 6, 8, 12, 16 and 18 with the blades angle being at -15°, -5°, 0°, 5° and 15°, respectively. Tests were undertaken at open type circuit wind tunnel. The results showed that the maximum power coefficient of the wind turbine at 16 blades and angle of 5° with an average of 0.26 which had 4.5 % increase in power compared to that of turbines the baseline. Finally, the cut in wind speed and the rev up time was 2.32 m/s and 25 s, respectively.

Design, simulation and performance evaluation of vertical axis helical wind turbine

This report is all about the design, simulation, fabrication, and performance evaluation of the VAHWT. The experimental data obtained via testing and data from CFD approach are used for performance evaluation. From the data obtained experimentally, the VAHWT so fabricated has been found to operate at the low cut-in speed of 3.18 m/s and maximum power output has been found to be 2.656 watts at the wind speed of 8 m/s. The maximum rpm of the rotor blade is recorded to be 722.2 rpm at the velocity of 11.53 m/s signifying its potentiality of wind power production. Besides, the data so obtained from both the process when analyzed through graph plots, has shown the similar nature slope wise. This simply signifies the generation of satisfactory data via experiment. In addition, the mechanical losses has shown difference between the experimental and data obtained via CFD approach. At the end, when applying CFD approach for evaluation of maximum efficient turbine varying the aspect ratio, has shown the turbine with aspect ratio of 0.6531 to be the most efficient with performance coefficient of 36.396%. However due to limitation in RPM and Test rig, the rotor blade with aspect ratio of 0.6956 was fabricated and used for evaluation experimentally. The data so obtained from both the process were concluded to be relevant to each other. Thus, the detail study on this project has led to the need and opportunity of VAHWT to be further researched and can be developed as a good source of energy producing system. It can also be economical method of power extraction from wind in the countries like Nepal with growing urbanization.

Analysis and implementation of a drag-type vertical-axis wind turbine for small distributed wind energy systems

This article investigates a drag-type vertical-axis wind turbine that is targeted for small-scale wind energy system applications. Based on aerodynamics models, the three-dimensional simulation studies have been carried out to obtain the force distributions along blades and eventually the torque and power coefficients for different vertical-axis wind turbine configurations. An optimal vertical-axis wind turbine configuration is chosen based on the comparative analysis, and a 2 kW prototype system has been implemented based on the design. The effectiveness of the three-dimensional models and simulation results has been verified by the measured data from the actual vertical-axis wind turbine system. The wake impacts to the vertical-axis wind turbine caused by nearby objects are also analyzed. The simulation results and the actual operation experiences show that the proposed system has the characteristics of low cut-in speed, high power density, and robustness to adjacent objects (such as buildings and other wind turbines), which make it suitable for small-scale wind energy systems in populated areas including urban environment.

Wind Energy Potential in Gaza Strip-Palestine state

In this study, wind speed and direction data provided by Meteoblue AG-Switzerland as hourly time-series for 16 years from 2000 to 2015 for selected three cities in Gaza Strip, are used directly to evaluate the wind energy in the three selected sites which are geographically presenting the entire Strip. Jabalia is located in the North of Gaza Strip, Deir-albalah in the Middle and Rafah in the South. Th wind rose diagrams have been depicted by using WRPLOT view 7.0.0 (wind rose plots for meteorological data fromLake Environmental, 2011). Th statistical analysis of the data shows that; Rafah city is the fist candidate to establish a wind farm in the entire Palestinian territory. Th reason that, Rafah has the highest wind energy potential than the other sites. Th second reason is that Rafah is located on the border crossing to Egypt, which facilitates the transfer of machinery, experts, and reduces transport and communication expanses. In addition to low population density, which increases the economic feasibility of utilizing wind energy at this location for remote area applications. Th analysis has been done for a large types of wind turbines types.Gamesa G128-4.5 WT, which is manufactured for classes I and II wind speeds with low cut-in speed, was selected for our project. Th estimated annual energy is 15,962 MWh/turbine, with an average utility factor of 40.4%; to cover the shortage of 200 MW we need to 110 WTs. Th required area for the wind farm is estimated to be 43 km2

Cogging Torque Reduction Based on a New Pre-Slot Technique for a Small Wind Generator

Cogging torque is a pulsating, parasitic, and undesired torque ripple intrinsic of the design of a permanent magnet synchronous generator (PMSG), which should be minimized due to its adverse effects: vibration and noise. In addition, as aerodynamic power is low during start-up at low wind speeds in small wind energy systems, the cogging torque must be as low as possible to achieve a low cut-in speed. A novel mitigation technique using compound pre-slotting, based on a combination of magnetic and non-magnetic materials, is investigated. The finite element technique is used to calculate the cogging torque of a real PMSG design for a small wind turbine, with and without using compound pre-slotting. The results show that cogging torque can be reduced by a factor of 48% with this technique, while avoiding the main drawback of the conventional closed slot technique: the reduction of induced voltage due to leakage flux between stator teeth. Furthermore, through a combination of pre-slotting and other cogging torque optimization techniques, cogging torque can be reduced by 84% for a given design.

Optimization of small wind turbine blades using improved blade element momentum theory

Typically, it is desired to operate the wind turbine at the maximum power point. However, in small wind turbines which have a storage system integrated with them, harvesting as much energy as possible is more crucial. This may be achieved by reducing the cut-in speed while maximizing the mechanical power. These two goals may be achieved by optimizing the turbine blades. In this article, the turbine blades are optimized using improved blade element momentum theory including Viterna-Corrigan stall model with the objective to yield low cut-in speed and high power level. Using the blade element momentum analysis, the power coefficient curves as functions of tip-speed ratio at various range of wind speeds are obtained for the optimized turbine. Using MATLAB/Simulink tool, a wind energy system, which consists of a wind turbine, permanent magnet synchronous generator and a resistive load, is simulated. The curves obtained from the blade element momentum analysis are used to emulate the wind turbine. The results obtained from the simulation are compared to experimental results. It is noticed that the wind turbine may be optimized to harvest more energy.

CFD performance enhancement of a low cut-in speed current Vertical Tidal Turbine through the nested hybridization of Savonius and Darrieus

This paper aims to enhance through two-dimensional numerical CFD simulations the hydrodynamic performance of a low cut-in speed current Vertical Axis Tidal Turbine (VATT) by means of the nested hybridization of Savonius and Darrieus. In fact, the hybrid turbine offers several coupling scenarios. In this work, the nested coupling has been used for Darrieus and Savonius to design the hybrid turbine model. Moreover, the effect of the rotational velocities of Savonius and Darrieus turbines, weather synchronized/desynchronized, identical/inverse rotational direction of the assessed rotors has been investigated.OpenFoam code was used to evaluate the hydrodynamic performance of the nested hybrid turbines, and to investigate their torque and power coefficients. This code is based on an Unsteady Reynolds Averaged Navier Stocks (URANS) approach coupled with k-ω Shear Stress Transport (SST) turbulence model. URANS models were validated against the literature results by performing 2D simulations on Savonius and Darrieus wind turbines. Therefore, the turbine’s behavior was studied and the overall performance efficiency of the nested hybrid design was enhanced over a defined Tip Speed Ratio (TSR) range. The main founding of this study was that the hybrid asynchronous coupling of Savonius and Darrieus (Identical rotational direction for the two rotors) is providing the effective performances compared to the other hybrid studied configurations.