Introduction
⌅Accelerated global warming is caused by human action and the excessive emission of greenhouse gases into the Earth's atmosphere (Meneses-Ruiz et al., 2018MENESES-RUIZ, E.; ROIG-RASSI, A.; PAZ, E.; ALONSO, D.; ALVARADO, J.: “Factores de emisión de CO, CO2, NOx y SO2 para instalaciones generadoras de electricidad en Cuba”, Revista Cubana de Meteorología, 24(1): 1-9, 2018, ISSN: 2664-0880.). Greenhouse gas emissions are produced in part by the burning of fossil fuels derived from petroleum (Meneses-Ruiz et al., 2018MENESES-RUIZ, E.; ROIG-RASSI, A.; PAZ, E.; ALONSO, D.; ALVARADO, J.: “Factores de emisión de CO, CO2, NOx y SO2 para instalaciones generadoras de electricidad en Cuba”, Revista Cubana de Meteorología, 24(1): 1-9, 2018, ISSN: 2664-0880.). About 86% of the world's carbon dioxide emissions come from the burning of fossil fuels for energy and material production (SE: Banco Mundial, 2023SE: BANCO MUNDIAL: “BIRF AIF IFC MIGA CIADI, Grupo Banco Mundial energy overview”, BIRF AIF IFC MIGA CIADI, 2023, Disponible en: https://www.bancomundial.org/es/topic/energy/overview ). Fossil fuels comprise 80% of the current global primary energy demand Elzinga (2023)ELZINGA, S. F.: United Nations. Papel de los combustibles fosiles en un sistema energético sostenible, Crónica ONU, 2023. https://www.un.org/es/chronicle/article/el-papel-de-los-combustibles-fosiles-en-un-sistema-energetico-sostenible Nearly 675 million people remain without electricity worldwide. Around 2.3 billion people rely on polluting traditional fuels and technologies to cook their food (SE: Banco Mundial, 2023SE: BANCO MUNDIAL: “BIRF AIF IFC MIGA CIADI, Grupo Banco Mundial energy overview”, BIRF AIF IFC MIGA CIADI, 2023, Disponible en: https://www.bancomundial.org/es/topic/energy/overview ).
Wind energy technology can be transformative for many developing countries, particularly vertical-axis wind turbines, which have characteristics that make them ideal for rural and urban applications, at low altitudes and with low wind speeds Damota (2022)DAMOTA, B.J.: Perfil de pala de turbina eólica de eje vertical de diseño bioinspirado: estudio comparativo y optimización mdediante modelo CFD parametrizado, Universidad Politécnica de Madrid, España, Tesis de grado, Madrid, España, 2022.. The idea then arises that the development of vertical wind turbines using indigenous technology in Cuba can contribute to energy autonomy in different sectors of society. Following Decree Law 345 on the application of renewable energy (GOC-Cuba, 2019GOC-CUBA: "Decreto No. 345/2019. Consejo de Estado de la República de Cuba", Gaceta Oficial de la República de Cuba (GOG-2019-1064-095), 2019. ISSN: 0864-0793, e-ISSN: 1682-7511, https://www.gacetaoficial.gob.cu/es/decreto-ley-345-de-2019-de-consejo-estado ).
The Varona Metal-Mechanical Company is working on the development of small wind turbines, a project recently launched in 2024 (Annex 1). To achieve this goal, the company has the ongoing guidance of specialists from the Faculty of Mechanics at the José Antonio Echeverría Technological University of Havana (CUJAE).
The main objective of this work is to evaluate the design of the Darrieus vertical wind turbines through computer-assisted simulation in order to analyze their performance during operation.
Materials and methods
⌅Nomenclature
⌅-
A: Swept area.
-
c: Chord.
-
d: Solidity.
-
e: Drag coefficient.
-
f: Lift coefficient.
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g: Moment coefficient.
-
h: Power coefficient.
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d: Rotor diameter.
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h: Drag force.
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i: Lift force.
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h: Rotor height.
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p: Turbine power.
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pd: Available power.
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v: Wind speed.
-
α: Angle of attack.
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h: Air density.
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Ω: Angular velocity.
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RAR: Rotor aspect ratio.
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RAA: Blade aspect ratio.
-
TSR: Tip speed ratio.
Materials
⌅Methodology
⌅The methodology established for obtaining the rotor design is shown in Figure 1 and described below.
Design requirements
⌅To begin the design, a field investigation must be conducted to define the area and operating conditions of the wind turbine. First, the province of Havana, at the José Antonio Echeverría Technological University of Havana (CUJAE), was taken as a reference location. Its location is approximately 57 meters above sea level Bader et al. (2025)BADER, N.; ZURFLUH, N.; SHIN, J.; SCHLÖGL, S.: “Meteoblue City Climate Model (mCCM): High-resolution Modeling for Urban Heatwave Management”, En: 105th Annual AMS Meeting 2025, vol. 105, p. 452735, 2025. https://www.meteoblue.com/es/tiempo/semana/la-habana_cuba_3553478 , which provides a working fluid density of 1.173 (Méndez, 2023MÉNDEZ, A.M.: Contribución desde el diseño, a la tecnología cubana para producción de Aerogeneradores de Eje Vertical, Inst. Universidad Tecnológica de la Habana «José Antonio Echaverría», Mecánica Aplicada, La Habana, Cuba, 2023.). In addition to this, other characteristics that demonstrate the climatic parameters in the city of Havana to which the prototypes will be subjected during operation must be taken into account. These are presented in Table 1. These measurements are from January to December of the last 30 years, based on data from the Meteoblue meteorological station in Basel (Bader et al., 2025BADER, N.; ZURFLUH, N.; SHIN, J.; SCHLÖGL, S.: “Meteoblue City Climate Model (mCCM): High-resolution Modeling for Urban Heatwave Management”, En: 105th Annual AMS Meeting 2025, vol. 105, p. 452735, 2025. https://www.meteoblue.com/es/tiempo/semana/la-habana_cuba_3553478 ).
| Annual Data | Average |
|---|---|
| Average Daily Maximum Temperature °C | 29,67 |
| Average Daily Minimum Temperature °C | 20,33 |
| Average Hot Day Temperature °C | 32,50 |
| Average Cold Night Temperature °C | 16,58 |
| Total Precipitation (mm) | 38,33 |
NACA Airfoil Evaluation and Selection
⌅NACA airfoils are a series of profiles created by the National Advisory Committee for Aeronautics (NACA), a United States federal agency founded on March 3, 1915 (Jankovsky et al., 2025JANKOVSKY, A.; NAWASH, N.; MÉNDEZ, J.: NASA Electric Aircraft Testbed (NEAT) Summary of Capabilities Version 3.0, July 2024, Inst. National Aeronautics and Space Administration, USA, 2025.). Figure 2 summarizes the main components of an airfoil.
When selecting a suitable profile, it was decided to use pre-built and highly tested airfoils to easily obtain information and avoid the testing required when creating a proprietary profile.
There are hundreds of profiles in the NACA line, but only three were considered. These are NACA 0018, NACA 4412, and NACA 61300. See Figure 3 below.
Qblade, by Qblade Team (2019), is an open-source software that uses XFoil/Xfrl5 to help users quickly design and calculate an airfoil performance. It can then be directly integrated into a wind turbine rotor design and simulated.
The first step is to perform a simulation to obtain the coefficients, and, of the airfoils over a sweep of angles of attack between 𝛼=−10° and 𝛼=+20°. The results are shown in Figure 4.
According to the results obtained, shown in Figure 4, the NACA 4412 airfoils offer the best aerodynamic efficiencies ( / ) compared to the other airfoils studied.
Now it is necessary to transform the coordinates from polar coordinates to 360° coordinates.
The dynamic pitch control system with its actuators was not implemented in this project (the pitch will be fixed at 0°), so it is advisable to have a NACA that offers high aerodynamic efficiency over a wider angle of attack range.
Rotor proposal
⌅Rotor solidity can be interpreted as the ratio of the blade's geometric area to the area swept by the rotor:
The specific rotor speed and power coefficient directly depend on the value of the rotor's solidity. High-solidity turbines produce high torque at low speeds (solidity up to 0.8), while low-solidity turbines produce lower torque but higher speed, which is desirable for power generation rotors (Quintero, 2016QUINTERO, S. Z.: Pruebas de rendimiento de una turbina eólica de eje vertical con perfiles aerodinámicos curvados. Bogotá D.C., 2016.). This parameter should be selected between value between 0.1 and 0.25 (Bernardo, 2018BERNARDO, R.S.: Estudio aerodinámico de un aerogenerador de eje vertical mediante técnicas de cálculo CFD, Universidad Politécnica de Madrid, España, TFG. Tesis de Grado en Ingeniería Mecánica, Madrid, España, 2018.).
The turbine: a greater number of blades results in more constant torque on the shaft, reducing fatigue. Furthermore, it allows the turbine to start without being limited to specific high-torque positions. However, it is important to keep in mind that the number of blades significantly affects rotor solidity (Quintero, 2016QUINTERO, S. Z.: Pruebas de rendimiento de una turbina eólica de eje vertical con perfiles aerodinámicos curvados. Bogotá D.C., 2016.).
The rotor aspect ratio relates the height of the blades to the rotor diameter. Increasing this value increases the shaft's angular velocity, thus making power generation more efficient (Quintero, 2016QUINTERO, S. Z.: Pruebas de rendimiento de una turbina eólica de eje vertical con perfiles aerodinámicos curvados. Bogotá D.C., 2016.).
The blade aspect ratio relates the height of the blades to their chord. The longer the rotor blades, the more the losses generated by the vortices at the wing tips are attenuated; consequently, increasing the blade aspect ratio increases the turbine's efficiency (Quintero, 2016QUINTERO, S. Z.: Pruebas de rendimiento de una turbina eólica de eje vertical con perfiles aerodinámicos curvados. Bogotá D.C., 2016.). Reducing the aspect ratio worsens the performance of the wind turbine blade. In the case of VAWTs with straight blades, the use of long, thin blades with a high blade aspect ratio is recommended (Bernardo, 2018BERNARDO, R.S.: Estudio aerodinámico de un aerogenerador de eje vertical mediante técnicas de cálculo CFD, Universidad Politécnica de Madrid, España, TFG. Tesis de Grado en Ingeniería Mecánica, Madrid, España, 2018.).
Below are the proposed design specifications for the rotor to be used during testing for this project:
| Rotor Parameter | |
|---|---|
| D (m) | 2 |
| H (m) | 2 |
| A (m2) | 4 |
| n (-) | 4 |
| c (m) | 0.2 |
| σ (-) | 0.51 |
| RAR (-) | 1 |
| RAA (-) | 10 |
The preliminary design of the rotor is presented in the following image, figure 6.
DMS simulation analysis
⌅The simulations are based on the Double Multiple Streamtube (DMS) model. This model was developed by Ion Paraschivoiu for the analysis of Darrieus rotors. It is an advanced derivation of the actuator disk theory combined with Blade Element Momentum (BEM) theory (Jankovsky et al., 2025JANKOVSKY, A.; NAWASH, N.; MÉNDEZ, J.: NASA Electric Aircraft Testbed (NEAT) Summary of Capabilities Version 3.0, July 2024, Inst. National Aeronautics and Space Administration, USA, 2025.).
DMS Rotor Simulation
⌅For each rotor type, there is a Cp range; this can also be defined as the power obtained relative to the available wind power (Fraire, 2020FRAIRE, D. J.: Diseño de un aerogenerador de eje vertcal para uso urbano de 3 kW, Villa María, 2020.).
A more useful way to determine wind turbine efficiency is to use the tangential velocity ratio (TSR) (Fraire, 2020FRAIRE, D. J.: Diseño de un aerogenerador de eje vertcal para uso urbano de 3 kW, Villa María, 2020.).
When calculating an estimate of our project's Cp, we see that it is directly related to TSR (λ).
To determine Cp, the simulation parameters are:
Results and discussion
⌅The results of the rotor simulations using the DMS method are shown in Figure 7 below.
Analyzing the results obtained in the Rotor DMS Simulation, for a constant wind speed of 5.69 m/s, the wide operating range can be appreciated, which is of great benefit because, for a given wind speed, it has a wide variety of rotational speeds; or vice versa, for a given rotational speed, it will have a wider range of wind speeds, where the turbine is able to fully harness the wind's energy.
The turbine with the NACA 4412 profile shows the highest power coefficient due to its high lift coefficient compared to the other profiles, but it also has the lowest TSR amplitude. The NACA 0018 turbine presents balanced Cp results and a wide TSR range, its line is clean due to its symmetrical profile. The turbine with the NACA 61300 profile has the lowest Cp in the TSR range 1-2, but at the same time it has the widest TSR amplitude profile and compared to the others it is the one that maintains a Cp above 0.4 for most of its line.
If the torque coefficient is plotted against the TSR, the characteristic curve in Figure 8 is obtained.
Figure 8 shows the variation in the torque produced by the wind turbine as a function of its rotational speed.
One of the disadvantages of H-Darrieus wind turbines is that they sometimes require a high starting torque due to their negative torque coefficient values for TSR close to zero. However, based on the results obtained in the simulation of these profiles configured for the rotor dimensions in the aforementioned section, this characteristic is not met, which is why they offer good results when breaking inertia and initiating rotational motion.
Multi-Parameter DMS Simulation
⌅In this simulation, the rotor simulation range can be selected, i.e., maximum, minimum, and increment values for wind speed, rotation speed, and pitch angle. Power values can be obtained versus wind speed or versus rotation speed, which are very useful for characterizing turbines for energy production (Barrragán, 2015BARRRAGÁN, J.M.: Diseño y optimización de una mini-turbina eólica mediante técnicas numéricas, Universidad Tecnológica de La Habana (CUJAE), Tesis de grado, 2015.). Figure 9 shows the configured wind speeds of 1-10 m/s.
Below, the DMS Multi Parameter simulation of power in relation to the min-1 of the NACA 0018, 4412 and 61300 respectively is shown in Figures 10, 11 and 12.
Analyzing the results obtained in the Multi Parameter DMS Simulation, for a variety of wind speeds ranging from 1-10 m/s and a range of 100-400 min-1.
Tables 3, 4, and 5 show the simulation results for the NACA 0018, NACA 4412, and NACA 61300, in that order, respectively.
| Blade NACA 0018 Simulation | |||||
|---|---|---|---|---|---|
| v(m/s) | min-1 | P [W] | v(m/s) | min-1 | P [W] |
| 1 | 100 | -0,63646 | 2 | 100 | 4,64799 |
| 200 | -5,09827 | 200 | -5,09166 | ||
| 300 | -17,2447 | 300 | -17,0402 | ||
| 400 | -40,8948 | 400 | -40,7862 | ||
| 3 | 100 | 28,7128 | 4 | 100 | 79,5447 |
| 200 | -2,70256 | 200 | 37,1839 | ||
| 300 | -17,1844 | 300 | -42,1842 | ||
| 400 | -39,9081 | 400 | -40,7333 | ||
| 5 | 100 | 111,217 | 6 | 100 | 94,0231 |
| 200 | 105,044 | 200 | 229,702 | ||
| 300 | 29,372 | 300 | 125,496 | ||
| 400 | -135,319 | 400 | -21,6205 | ||
| 7 | 100 | 79,7104 | 8 | 100 | 69,8496 |
| 200 | 401,254 | 200 | 636,358 | ||
| 300 | 263,349 | 300 | 473,65 | ||
| 400 | 120,955 | 400 | 297,472 | ||
| 9 | 100 | 63,0677 | 10 | 100 | 61,2419 |
| 200 | 887,046 | 200 | 889,737 | ||
| 300 | 775,246 | 300 | 1142,59 | ||
| 400 | 525,78 | 400 | 840,353 | ||
| Blade NACA 4412 Simulation | |||||
|---|---|---|---|---|---|
| v (m/s) | min-1 | P [W] | v (m/s) | min-1 | P [W] |
| 1 | 100 | -3,18588 | 2 | 100 | -1,8432 |
| 200 | -21,6937 | 200 | -25,487 | ||
| 300 | -70,2326 | 300 | -76,044 | ||
| 400 | -189,615 | 400 | -173,55 | ||
| 3 | 100 | 29,1418 | 4 | 100 | 61,1209 |
| 200 | -29,2681 | 200 | -14,746 | ||
| 300 | -86,0186 | 300 | -98,933 | ||
| 400 | -185,46 | 400 | -203,9 | ||
| 5 | 100 | 126,776 | 6 | 100 | 126,19 |
| 200 | 170,616 | 200 | 233,134 | ||
| 300 | -91,5401 | 300 | -49,767 | ||
| 400 | -227,688 | 400 | -234,15 | ||
| 7 | 100 | 110,646 | 8 | 100 | 100,369 |
| 200 | 318,869 | 200 | 488,967 | ||
| 300 | 516,228 | 300 | 640,671 | ||
| 400 | -199,036 | 400 | -117,97 | ||
| 9 | 100 | 95,3748 | 10 | 100 | 93,364 |
| 200 | 776,099 | 200 | 1014,21 | ||
| 300 | 786,828 | 300 | 966,108 | ||
| 400 | 49,1511 | 400 | 1364,92 | ||
| Blade NACA 6Blade NACA 61300 Simulation | |||||
|---|---|---|---|---|---|
| v (m/s) | min-1 | P [W] | v (m/s) | min-1 | P [W] |
| 1 | 100 | 1,04084 | 2 | 100 | 8,10093 |
| 200 | 7,91343 | 200 | 8,32672 | ||
| 300 | 26,6527 | 300 | 26,8777 | ||
| 400 | 63,1607 | 400 | 63,3074 | ||
| 3 | 100 | 29,0583 | 4 | 100 | 39,9098 |
| 200 | 23,7601 | 200 | 64,8074 | ||
| 300 | 28,1027 | 300 | 42,6056 | ||
| 400 | 63,9384 | 400 | 66,6138 | ||
| 5 | 100 | 29,5547 | 6 | 100 | 8,24862 |
| 200 | 123,491 | 200 | 232,467 | ||
| 300 | 122,485 | 300 | 218,725 | ||
| 400 | 87,1254 | 400 | 190,081 | ||
| 7 | 100 | -7,07141 | 8 | 100 | -19,022 |
| 200 | 359,973 | 200 | 319,278 | ||
| 300 | 339,362 | 300 | 509,953 | ||
| 400 | 344,77 | 400 | 518,459 | ||
| 9 | 100 | -27,888 | 10 | 100 | -34,049 |
| 200 | 362,926 | 200 | 236,437 | ||
| 300 | 784,575 | 300 | 1104,13 | ||
| 400 | 724,76 | 400 | 987,928 | ||
The graphs show how the turbine with the NACA 4412 profile produces greater maximum power compared to the NACA 0018 and NACA 61300 turbines, with the latter producing the lowest output. The NACA 61300 could be ruled out if only the aforementioned point were considered, but if a turbine that operates at a specific wind speed is desired, the turbine that produces the maximum power at that speed should be cho.
The amount of energy a wind turbine can generate depends greatly on the characteristics of the wind. Therefore, before installing a wind turbine, it is important to know the wind potential at the site. This parameter is essential when deciding which wind turbine to select.
In Havana, for example, the average minimum wind speed is around 3.33 m/s with a standard deviation of 0.53 m/s (16%), the average wind speed is 4.84 m/s, and the maximum wind speed is approximately 6.37 m/s with a standard deviation of 0.59 m/s (9%) (Méndez, 2023MÉNDEZ, A.M.: Contribución desde el diseño, a la tecnología cubana para producción de Aerogeneradores de Eje Vertical, Inst. Universidad Tecnológica de la Habana «José Antonio Echaverría», Mecánica Aplicada, La Habana, Cuba, 2023.).
With this in mind, it can be observed in Tables 3, 4, and 5 that turbines with NACA 0018 and NACA 4412 profiles, at wind speeds between 1 and 3 m/s, produce almost no power. It is from 4 m/s and above at low speeds of 100 and 200 RPM that they produce significant power. Above 4 m/s, the turbines begin to produce significant power, reaching 1.1 and 1.36 kW. However, the NACA 61300 rotor is capable of generating power at low wind speeds, as shown in Table 5.
Finally, in view of the results shown above, it can be stated that the best option of the turbines shown in this work corresponds to the NACA 61300 rotor, considering its power with respect to the others, for speeds below the design point, which can be useful in a region where wind conditions are variable.
Economic valuation and social contribution.
⌅Economic valuation
⌅For calculation purposes, this technical and economic evaluation model for small-scale wind energy projects is used. The turbine's electrical generation capacity is shown in Tables 6, 7, and 8 below, based on wind speeds of 1-10 m/s.
| Wind speed (m/s) | 1 | 2 | 3 |
|---|---|---|---|
| Useful power (W) | 63,16 | 63,31 | 63,94 |
| Power (W/day) | 1515,86 | 1519,38 | 1534,52 |
| Power in (kW/day) | 1,52 | 1,52 | 1,53 |
| Power (kW/month) | 45,48 | 45,58 | 46,04 |
| Power (kW/year) | 545,71 | 546,98 | 552,43 |
| Unit price kWh = $ | 15,02 | 15,05 | 15,18 |
| Annual unit price kWh = $ | 180,18 | 180,58 | 182,16 |
| Wind speed (m/s) | 4 | 5 | 6 |
|---|---|---|---|
| Useful power (W) | 66,61 | 123,49 | 232,47 |
| Power (W/day) | 1598,73 | 2963,78 | 5579,21 |
| Power (kW/day) | 1,60 | 2,96 | 5,58 |
| Power (kW/month) | 47,96 | 88,91 | 167,38 |
| Power (kWh/year) | 575,54 | 1066,96 | 2008,51 |
| Unit price kWh = $ | 15,84 | 29,34 | 111,38 |
| Annual unit price kWh = $ | 190,08 | 352,04 | 1336,58 |
| Wind speed (m/s) | 7 | 8 | 9 | 10 |
|---|---|---|---|---|
| Useful power (W) | 359,97 | 518,46 | 784,58 | 1104,13 |
| Power (W/day) | 8639,35 | 12443,02 | 18829,80 | 26499,12 |
| Power in (kW/day) | 8,64 | 12,44 | 18,83 | 26,50 |
| Power (kW/month) | 259,18 | 373,29 | 564,89 | 794,97 |
| Power (kW/year) | 3110,17 | 4479,49 | 6778,73 | 9539,68 |
| Unit price kWh = $ | 308,60 | 747,50 | 2128,08 | 4331,75 |
| Annual unit price kWh = $ | 3703,20 | 8970,00 | 25536,96 | 51981,00 |
Environmental Analysis
⌅It has been proven that wind technology is highly necessary today; however, according to studies, social empowerment has not been taken into account in many countries, as actions aimed at educating people have been lacking. In the case of Cuba, we are not exempt from this problem, and it is necessary to demonstrate the importance of harnessing wind energy based on vertical turbines.
Nominal power data were entered into the EPA (Meneses-Ruiz et al., 2018MENESES-RUIZ, E.; ROIG-RASSI, A.; PAZ, E.; ALONSO, D.; ALVARADO, J.: “Factores de emisión de CO, CO2, NOx y SO2 para instalaciones generadoras de electricidad en Cuba”, Revista Cubana de Meteorología, 24(1): 1-9, 2018, ISSN: 2664-0880.).
Greenhouse gas equivalency calculator (kWh avoided)
⌅This perspective focuses on the amount of energy that does not need to be generated from polluting sources, such as fossil fuels, thanks to the energy produced by the wind turbine.
| Kilowatt-hours avoided (kWh) | 1,1 |
| CO2 equivalent (t) | 0,0008 |
| Gallons of gasoline consumed | 0.086 |
| Gallons of diesel consumed | 0.075 |
| Pounds of coal burned | 0.861 |
| Home energy use for one year | 0.0001 |
| Household electricity use for one year | 0.0001 |
| Barrels of oil consumed | 0.002 |
| Propane cylinders used for home barbecues | 0.035 |
| Number of smartphones charged | 93.5 |
| Tons of waste recycled instead of being disposed of in landfills (t) | 0.0003 |
| Trash bags of waste recycled instead of being disposed of in landfills | 0.033 |
| Urban tree seedlings grown for 10 years | 0.013 |
Conclusions
⌅This paper presents the analysis of three turbines with NACA 0018, NACA 4412, and NACA 61300 profiles, for wind speeds of (1-10) m/s and a rotor diameter of 2 m. These parameters were chosen to study the utilization of wind energy in areas with low wind speeds.
Only 4-blade turbines were analyzed, and simulations were performed using the QBlade program. It was found that the turbines studied have similar maximum power; however, observing their characteristic curves, it was determined that the turbine with the NACA 61300 profile represented the best option.
Analyzing the results in Tables 6, 7, and 8, it can be assumed that the product meets the energy needs of a residential home.
The NACA 61300 profile turbine offers a viable option for optimal wind energy utilization in urban and rural areas with low wind parameters.