Blades on a Vertical Axis Wind Turbine (VAWT) experience curved streamlines, caused by the rotati... more Blades on a Vertical Axis Wind Turbine (VAWT) experience curved streamlines, caused by the rotation of the turbine. This phenomenon is known as flow curvature and has effects on the aerodynamic loading of the blades. Several authors have proposed methods to account for flow curvature, resulting in methods to transform the original airfoil in curved flow to a virtual airfoil, which can be analysed in straight flow. This paper reviews multiple of such virtual airfoil transformations and compares the outcomes. All methods show good correspondence to the curved flow pressure distribution , but small errors remain that are intrinsic to the conformal methods used. It is shown that VAWT rotation is equivalent to an eternal pitching motion. Using this similarity, flow curvature modeling has been added to the airfoil analysis tool XFOIL. The various changes have been made in the inviscid solver, in a way that the viscous solver need not to be changed. Nomenclature C p = pressure coefficient c = airfoil chord q = airfoil surface velocity q 0 = airfoil body velocity q ∞ = freestream velocity R = turbine radius r = rotational velocity arm u p = local panel horizontal velocity u x = airfoil horizontal surface velocity u ∞ = freestream horizontal velocity v p = local panel vertical velocity v y = airfoil vertical surface velocity v ∞ = freestream vertical velocity x = airfoil horizontal coordinate x p = pitch location horizontal coordinate y = airfoil vertical coordinate y p = pitch location vertical coordinate α = angle of attack γ = vorticity Φ = velocity potential Ψ = velocity streamfunction Ω = VAWT rotational velocity ω = airfoil pitch rate
The primary objective of this paper is to investigate a cyclonic domestic scale vertical axis win... more The primary objective of this paper is to investigate a cyclonic domestic scale vertical axis wind turbine with semicircular shaped blades under a range of wind speeds. A 16-bladed rotor was initially designed and its torques and angular speeds were measured over a range of wind speeds using a wind tunnel. Additionally, a cowling device was developed to enhance the turbine efficiency by directing the air flow from the rear blades into the atmosphere. Another 8-bladed rotor was also manufactured to investigate the effect of blade number on the maximum power generation. The aerodynamic performance of the cowling device was also investigated. Maximum power curves as a function of wind speeds were established for each configuration. The results indicated that the 16-bladed wind turbine can be used for domestic scale wind power generation. The results show that the cowling device has positive effect to increase the rotor speed to a significant amount. With the use of the cowling device, the average rotor speed increased by about 26% for the 16-bladed rotor compared to the baseline configuration. A significant increase (about 40%) of rotor speed was also found for the 8-bladed rotor with the cowling device. The results also indicated that the cowling device can be used to increase the power output of this cyclonic type vertical axis wind turbine especially with a reduce number of blades.
The following work represents the most recent advances in design and testing of vertical axis win... more The following work represents the most recent advances in design and testing of vertical axis wind turbines (VAWT) rotors. VAWTs have received much attention as of late due to proposed advantages in small scale and off grid wind power generation. Thus, many recent works have surfaced involving analysis, design and optimization of VAWT rotors in order to more efficiently convert wind energy to electricity or other readily usable means. This paper is a collection of most of the recent literature works involving VAWT rotor design and testing, the majority of which published after 2005. We discuss research in the designing of various lift based rotors as well as some drag based rotors, hybrids, and various others. The recent work in this area suggests VAWT capacity could dramatically increase in the near future, and play a vital role in obtaining cleaner, more sustainable energy when global energy demand is increasing at an unprecedented rate.
—The objective of this paper is to compare five different generator systems for wind turbines, na... more —The objective of this paper is to compare five different generator systems for wind turbines, namely the doubly-fed induction generator with three-stage gearbox (DFIG3G), the direct-drive synchronous generator with electrical excitation (DDSG), the direct-drive permanent-megnet generator (DDPMG), the permanent-magnet generator with single stage gearbox (PMG1G), and the doubly-fed induction generator with single-stage gearbox (DFIG1G). The comparison is based on cost and annual energy yield for a given wind climate. The DFIG3G is a cheap solution using standard components. The DFIG1G seems the most attractive in terms of energy yield divided by cost. The DDPMG has the highest energy yield, but although it is cheaper than the DDSG, it is more expensive than the generator systems with gearbox. Index Terms—Direct-drive, doubly fed induction generator (DFIG), permanent-magnet generator, single-stage gearbox, synchronous generator, wind turbine.
Wind energy technology has seen steady growth in the energy market as a clean, renewable source o... more Wind energy technology has seen steady growth in the energy market as a clean, renewable source of energy. This has brought attention to areas with moderate wind energy potentials. Darrieus type Vertical Axis Wind Turbines (VAWTs) allows capturing of this potential for energy production at a costeffective scale. To improve the performance of these turbines their design needs to be modified. With better manufacturing methods currently available cambered blades are being investigated to improve the performance of these turbines. In particular, turbine solidity is investigated in this paper due to different chord lengths of the blades. The analysis is conducted following high fidelity CFD modeling in unsteady, turbulent regimes with a sliding/rotating mesh configuration to emphasize the role of rotor blades interaction. The study showed that low solidity turbines with cambered blades operate at low coefficients of performance (C P ) over a large range of tip speed ratios (TSRs). High solidity turbines have much higher C P, but at smaller TSRs and short range of TSRs. Medium solidity turbines are faced with considerable interaction which compromises their operation at TSRs as low as 1.
Straight Darrieus wind turbine has attractive characteristics such as the ability to accept wind ... more Straight Darrieus wind turbine has attractive characteristics such as the ability to accept wind from random direction and easy installation and maintenance. But its aerodynamic performance is very complicated, especially for the existence of dynamic stall. How to get better aerodynamic performance arouses lots of interests in the design procedure of a straight Darrieus wind turbine. In this paper, mainly the effects of number of blades and tip speed ratio are discussed. Based on the numerical investigation, an assumed asymmetric straight Darrieus wind turbine is proposed to improve the averaged power coefficient. As to the numerical method, the flow around the turbine is simulated by solving the 2D unsteady Navier-Stokes equation combined with continuous equation. The time marching method on a body-fitted coordinate system based on MAC (Marker-and-Cell) method is used. O-type grid is generated for the whole calculation domain. The characteristics of tangential and normal force are discussed related with dynamic stall of the blade. Averaged power coefficient per period of rotating is calculated to evaluate the eligibility of the turbine.
Increasing demand in energy facilitated the need of clean energy such as wind energy. Residences,... more Increasing demand in energy facilitated the need of clean energy such as wind energy. Residences, buildings and commercial sites needs more power, but also continuous power. Important facilities such as wireless or radio sets requires small amount of energy, but with a continuous supply. This project was done to design and construct a vertical axis wind turbine for small scale use. After an introduction about the historical background of wind turbine, the report deals with a more accurate analysis of the main type of vertical axis wind turbine, showing their characteristics, advantages and disadvantages, differences between vertical axis wind turbine and horizontal axis wind turbine and their operations. The parameter of the wind turbines was discussed and the generators (stator) that can be used to connect the wind mill to the electricity grid are reported as well. Several statistics are also presented, in order to explain how the development of the wind energy in Nigeria. Results from trials shows that as the speed increases, there is increase in voltage and this in turn implies a watt change at different speeds. This also implies that when there is high wind, there is a higher rpm. The turbine fulfilled all specifications such as efficiency above 80%, 33Watt output power and likewise the capacity is adequate for its purpose and was proven to be efficient in generation of current.
The effect of an upstream flat deflector on the power output of two counter-rotating straight-bla... more The effect of an upstream flat deflector on the power output of two counter-rotating straight-bladed vertical-axis wind turbines (VAWTs) was investigated experimentally. Although many studies on the deflector effect have been done for a drag-based Savonius VAWT, there is little information on the performance of a lift-based VAWT with a deflector. If a flat vertical plate is normal to the free-stream wind direction, the local wind speed outside the near-wake region of the plate is larger than the freestream velocity. Thus, when each of the counter-rotating turbines is positioned outside the near-wake region, its power output increases significantly. The power output increase with the deflector installed is dependent on the width and height of the deflector and the turbine position relative to the deflector.
Recently, the straight-bladed vertical axis wind turbine (SB-VAWT) receives more and more attenti... more Recently, the straight-bladed vertical axis wind turbine (SB-VAWT) receives more and more attentions for its simple design, low cost, and good maintenance. The torque performance of the SB-VAWT is greatly affected by the blade airfoil. In order to research the static torque characteristics of SB-VAWT with symmetrical and non-symmetrical blade airfoil, numerical simulations by 2D CFD method were carried out on three kinds of blade airfoils including NACA0018, NACA2418 and NACA4418 at different azimuth angles. Furthermore, the static torque coefficient of the SB-VAWT with four blades with the three kinds of blade airfoils was calculated. The pressure and velocity fields were also obtained to analyze the static torque performance. Based on these results, the effects of blade airfoils on the starting torque performance of the SB-VAWT were compared and discussed.
A new computational model for the aerodynamics of vertical-axis wind turbines is introduced. It i... more A new computational model for the aerodynamics of vertical-axis wind turbines is introduced. It is based on the double-multiple streamtube concept and it incorporates the capacity of dealing with rotors whose blades follow oval-trajectories at variable setting-angles. We applied this model to the study of the aerodynamics of an innovative concept in extra-large wind-power plants: the VGOT (variable-geometry oval-trajectory) Darrieus wind turbine. Due to the especial geometric characteristics of the VGOT Darrieus, it was necessary to propose three new non-dimensional parameters to quantify its performance under different wind-conditions: the equivalent power coefficient, the equivalent solidity coefficient and the trajectory efficiency. We show some numerical results testing several rotor configurations working under different wind scenarios. r
This paper describes an attempt to optimize the performance of the Vertical Axis Wind Turbines (V... more This paper describes an attempt to optimize the performance of the Vertical Axis Wind Turbines (VAWT) using active blade pitch control. The design of wind turbine chosen here is an H-type Darrieus VAWT which works on the lift force of the wind. Active Pitch controlled VAWT with individual pitch control of each blade along with vertical roller bearings in the system is done to obtain maximum coefficient of power harnessed from the wind turbine setup and increase the efficiency by 12.5%. The aerodynamic model is chosen based on the surface profile and NACA 4 digit series was found to be the most suitable category under which NACA 0018 aerofoil design parameters have been chosen for the VAWT blade design, based on the previous research.
A two-dimensional numerical simulation of the contribution of both inertial and aerodynamic force... more A two-dimensional numerical simulation of the contribution of both inertial and aerodynamic forces on the blade loads of a Vertical-Axis Wind Turbine (VAWT) is presented. After describing the computational model and the relative validation procedure, a complete campaign of simulations -based on full RANS unsteady calculations -is proposed for a three-bladed rotor architecture characterized by a NACA 0021 airfoil. For each analyzed angular velocity, the combined effect of pressure and viscous forces acting on every rotor blade are compared to the corresponding centrifugal forces, due to the revolution of the turbine, thus achieving a preliminary estimation of the correlation between overall rotor efficiency and structural blade loads.
Reynolds averaged Navier-Stokes equations and Realizable k model were used in this paper, and the... more Reynolds averaged Navier-Stokes equations and Realizable k model were used in this paper, and the two dimensional unsteady flow field of the vertical axis wind turbine was simulated numerically at different wind velocity. The calculation results showed that the velocity in the region of wind turbine s rotation was much larger than the air flow of the upstream. The length of the wind turbine s downstream wake dispersion region was increased with the increase of the wind velocity. There is a much larger value of the eddy in the rear region of the wind turbine s rotational blades. And eddy existed in the downstream region of the wind turbine, and the larger velocity of cross flow, the larger value of the downstream flow s eddy. When the rotational speed was constant, with the increase in wind velocity, the variation of the s total torque coefficient tended to smooth. The calculation results pointed out the direction for the follow-up study.
As the energy crisis is getting severe in the world it will be important to investigate alternati... more As the energy crisis is getting severe in the world it will be important to investigate alternative methods of generating power in ways different than, fossil fuels. In fact, one of the biggest sources of energy is all around us all of the time, the wind. Currently, horizontal axis wind turbines (HAWT) dominate the wind energy market due to their large size and high power generation characteristics. However, vertical axis wind turbines (VAWT) are capable of producing a lot of power, and offer many advantages for small-scale and domestic applications. One drawback of DARRIEUS type VAWT is their inability to reliably selfstart at low tip speed ratio. The details of different configurations and performance evaluation techniques along with the major findings of researchers on vertical axis wind turbines are reviewed in this paper. The main purpose of the study described here is to investigate effect of different design parameter on performance evaluation of VAWT.
The control of a wind turbine to the mean wind speed in a gusty wind results in very poor perform... more The control of a wind turbine to the mean wind speed in a gusty wind results in very poor performance. Fluctuations in wind speed with time constants shorter than the response time of a wind turbine results in operation away from optimum design conditions.
Increasing demand for energy in recent years has seen a rise in development of alternative energy... more Increasing demand for energy in recent years has seen a rise in development of alternative energy sources. Wind being one of the most abundant and easily available sources is an excellent alternative to conventional energy sources.
The paper aims to investigate the performance of the high aspect ratio vertical axis wind turbine... more The paper aims to investigate the performance of the high aspect ratio vertical axis wind turbine with numerical method and to present some experimental results. Aerodynamics with numerical method is a major prospect of the investigation. Computational fluid dynamic software, ANSYS CFX, is employed to analyze drag force generated from the influence of blade shape. Two types of turbine blades have been investigated with aerodynamics prospects, namely shape-design model and mechanism model. Power coefficient of each models are calculated and compared. Turning force to reverse force ratio has been used to compare different shapes of the turbine blade. It has been found that the mechanism model, with power coefficient of 16.2 per cent, offers better capability of harnessing wind energy than shape-design model.
This case study investigates the generator of a large offshore Vertical Axis Wind Turbine (VAWT).... more This case study investigates the generator of a large offshore Vertical Axis Wind Turbine (VAWT). In particular this case study focuses on the effect of the inherent cyclic torque loading of the VAWT on the generator in terms of the costs and losses experienced. A spectrum of torque control strategies were created based on the ratio q of the allowed electrical torque variation to the mechanical torque variation. Equations relating the copper and iron losses of the generator to this q factor were established and investigated for a test turbine. In addition the relationship between the allowed variation in electrical torque and the cost of the active materials of the generator was explored.
Blades on a Vertical Axis Wind Turbine (VAWT) experience curved streamlines, caused by the rotati... more Blades on a Vertical Axis Wind Turbine (VAWT) experience curved streamlines, caused by the rotation of the turbine. This phenomenon is known as flow curvature and has effects on the aerodynamic loading of the blades. Several authors have proposed methods to account for flow curvature, resulting in methods to transform the original airfoil in curved flow to a virtual airfoil, which can be analysed in straight flow. This paper reviews multiple of such virtual airfoil transformations and compares the outcomes. All methods show good correspondence to the curved flow pressure distribution , but small errors remain that are intrinsic to the conformal methods used. It is shown that VAWT rotation is equivalent to an eternal pitching motion. Using this similarity, flow curvature modeling has been added to the airfoil analysis tool XFOIL. The various changes have been made in the inviscid solver, in a way that the viscous solver need not to be changed. Nomenclature C p = pressure coefficient c = airfoil chord q = airfoil surface velocity q 0 = airfoil body velocity q ∞ = freestream velocity R = turbine radius r = rotational velocity arm u p = local panel horizontal velocity u x = airfoil horizontal surface velocity u ∞ = freestream horizontal velocity v p = local panel vertical velocity v y = airfoil vertical surface velocity v ∞ = freestream vertical velocity x = airfoil horizontal coordinate x p = pitch location horizontal coordinate y = airfoil vertical coordinate y p = pitch location vertical coordinate α = angle of attack γ = vorticity Φ = velocity potential Ψ = velocity streamfunction Ω = VAWT rotational velocity ω = airfoil pitch rate
The primary objective of this paper is to investigate a cyclonic domestic scale vertical axis win... more The primary objective of this paper is to investigate a cyclonic domestic scale vertical axis wind turbine with semicircular shaped blades under a range of wind speeds. A 16-bladed rotor was initially designed and its torques and angular speeds were measured over a range of wind speeds using a wind tunnel. Additionally, a cowling device was developed to enhance the turbine efficiency by directing the air flow from the rear blades into the atmosphere. Another 8-bladed rotor was also manufactured to investigate the effect of blade number on the maximum power generation. The aerodynamic performance of the cowling device was also investigated. Maximum power curves as a function of wind speeds were established for each configuration. The results indicated that the 16-bladed wind turbine can be used for domestic scale wind power generation. The results show that the cowling device has positive effect to increase the rotor speed to a significant amount. With the use of the cowling device, the average rotor speed increased by about 26% for the 16-bladed rotor compared to the baseline configuration. A significant increase (about 40%) of rotor speed was also found for the 8-bladed rotor with the cowling device. The results also indicated that the cowling device can be used to increase the power output of this cyclonic type vertical axis wind turbine especially with a reduce number of blades.
The following work represents the most recent advances in design and testing of vertical axis win... more The following work represents the most recent advances in design and testing of vertical axis wind turbines (VAWT) rotors. VAWTs have received much attention as of late due to proposed advantages in small scale and off grid wind power generation. Thus, many recent works have surfaced involving analysis, design and optimization of VAWT rotors in order to more efficiently convert wind energy to electricity or other readily usable means. This paper is a collection of most of the recent literature works involving VAWT rotor design and testing, the majority of which published after 2005. We discuss research in the designing of various lift based rotors as well as some drag based rotors, hybrids, and various others. The recent work in this area suggests VAWT capacity could dramatically increase in the near future, and play a vital role in obtaining cleaner, more sustainable energy when global energy demand is increasing at an unprecedented rate.
—The objective of this paper is to compare five different generator systems for wind turbines, na... more —The objective of this paper is to compare five different generator systems for wind turbines, namely the doubly-fed induction generator with three-stage gearbox (DFIG3G), the direct-drive synchronous generator with electrical excitation (DDSG), the direct-drive permanent-megnet generator (DDPMG), the permanent-magnet generator with single stage gearbox (PMG1G), and the doubly-fed induction generator with single-stage gearbox (DFIG1G). The comparison is based on cost and annual energy yield for a given wind climate. The DFIG3G is a cheap solution using standard components. The DFIG1G seems the most attractive in terms of energy yield divided by cost. The DDPMG has the highest energy yield, but although it is cheaper than the DDSG, it is more expensive than the generator systems with gearbox. Index Terms—Direct-drive, doubly fed induction generator (DFIG), permanent-magnet generator, single-stage gearbox, synchronous generator, wind turbine.
Wind energy technology has seen steady growth in the energy market as a clean, renewable source o... more Wind energy technology has seen steady growth in the energy market as a clean, renewable source of energy. This has brought attention to areas with moderate wind energy potentials. Darrieus type Vertical Axis Wind Turbines (VAWTs) allows capturing of this potential for energy production at a costeffective scale. To improve the performance of these turbines their design needs to be modified. With better manufacturing methods currently available cambered blades are being investigated to improve the performance of these turbines. In particular, turbine solidity is investigated in this paper due to different chord lengths of the blades. The analysis is conducted following high fidelity CFD modeling in unsteady, turbulent regimes with a sliding/rotating mesh configuration to emphasize the role of rotor blades interaction. The study showed that low solidity turbines with cambered blades operate at low coefficients of performance (C P ) over a large range of tip speed ratios (TSRs). High solidity turbines have much higher C P, but at smaller TSRs and short range of TSRs. Medium solidity turbines are faced with considerable interaction which compromises their operation at TSRs as low as 1.
Straight Darrieus wind turbine has attractive characteristics such as the ability to accept wind ... more Straight Darrieus wind turbine has attractive characteristics such as the ability to accept wind from random direction and easy installation and maintenance. But its aerodynamic performance is very complicated, especially for the existence of dynamic stall. How to get better aerodynamic performance arouses lots of interests in the design procedure of a straight Darrieus wind turbine. In this paper, mainly the effects of number of blades and tip speed ratio are discussed. Based on the numerical investigation, an assumed asymmetric straight Darrieus wind turbine is proposed to improve the averaged power coefficient. As to the numerical method, the flow around the turbine is simulated by solving the 2D unsteady Navier-Stokes equation combined with continuous equation. The time marching method on a body-fitted coordinate system based on MAC (Marker-and-Cell) method is used. O-type grid is generated for the whole calculation domain. The characteristics of tangential and normal force are discussed related with dynamic stall of the blade. Averaged power coefficient per period of rotating is calculated to evaluate the eligibility of the turbine.
Increasing demand in energy facilitated the need of clean energy such as wind energy. Residences,... more Increasing demand in energy facilitated the need of clean energy such as wind energy. Residences, buildings and commercial sites needs more power, but also continuous power. Important facilities such as wireless or radio sets requires small amount of energy, but with a continuous supply. This project was done to design and construct a vertical axis wind turbine for small scale use. After an introduction about the historical background of wind turbine, the report deals with a more accurate analysis of the main type of vertical axis wind turbine, showing their characteristics, advantages and disadvantages, differences between vertical axis wind turbine and horizontal axis wind turbine and their operations. The parameter of the wind turbines was discussed and the generators (stator) that can be used to connect the wind mill to the electricity grid are reported as well. Several statistics are also presented, in order to explain how the development of the wind energy in Nigeria. Results from trials shows that as the speed increases, there is increase in voltage and this in turn implies a watt change at different speeds. This also implies that when there is high wind, there is a higher rpm. The turbine fulfilled all specifications such as efficiency above 80%, 33Watt output power and likewise the capacity is adequate for its purpose and was proven to be efficient in generation of current.
The effect of an upstream flat deflector on the power output of two counter-rotating straight-bla... more The effect of an upstream flat deflector on the power output of two counter-rotating straight-bladed vertical-axis wind turbines (VAWTs) was investigated experimentally. Although many studies on the deflector effect have been done for a drag-based Savonius VAWT, there is little information on the performance of a lift-based VAWT with a deflector. If a flat vertical plate is normal to the free-stream wind direction, the local wind speed outside the near-wake region of the plate is larger than the freestream velocity. Thus, when each of the counter-rotating turbines is positioned outside the near-wake region, its power output increases significantly. The power output increase with the deflector installed is dependent on the width and height of the deflector and the turbine position relative to the deflector.
Recently, the straight-bladed vertical axis wind turbine (SB-VAWT) receives more and more attenti... more Recently, the straight-bladed vertical axis wind turbine (SB-VAWT) receives more and more attentions for its simple design, low cost, and good maintenance. The torque performance of the SB-VAWT is greatly affected by the blade airfoil. In order to research the static torque characteristics of SB-VAWT with symmetrical and non-symmetrical blade airfoil, numerical simulations by 2D CFD method were carried out on three kinds of blade airfoils including NACA0018, NACA2418 and NACA4418 at different azimuth angles. Furthermore, the static torque coefficient of the SB-VAWT with four blades with the three kinds of blade airfoils was calculated. The pressure and velocity fields were also obtained to analyze the static torque performance. Based on these results, the effects of blade airfoils on the starting torque performance of the SB-VAWT were compared and discussed.
A new computational model for the aerodynamics of vertical-axis wind turbines is introduced. It i... more A new computational model for the aerodynamics of vertical-axis wind turbines is introduced. It is based on the double-multiple streamtube concept and it incorporates the capacity of dealing with rotors whose blades follow oval-trajectories at variable setting-angles. We applied this model to the study of the aerodynamics of an innovative concept in extra-large wind-power plants: the VGOT (variable-geometry oval-trajectory) Darrieus wind turbine. Due to the especial geometric characteristics of the VGOT Darrieus, it was necessary to propose three new non-dimensional parameters to quantify its performance under different wind-conditions: the equivalent power coefficient, the equivalent solidity coefficient and the trajectory efficiency. We show some numerical results testing several rotor configurations working under different wind scenarios. r
This paper describes an attempt to optimize the performance of the Vertical Axis Wind Turbines (V... more This paper describes an attempt to optimize the performance of the Vertical Axis Wind Turbines (VAWT) using active blade pitch control. The design of wind turbine chosen here is an H-type Darrieus VAWT which works on the lift force of the wind. Active Pitch controlled VAWT with individual pitch control of each blade along with vertical roller bearings in the system is done to obtain maximum coefficient of power harnessed from the wind turbine setup and increase the efficiency by 12.5%. The aerodynamic model is chosen based on the surface profile and NACA 4 digit series was found to be the most suitable category under which NACA 0018 aerofoil design parameters have been chosen for the VAWT blade design, based on the previous research.
A two-dimensional numerical simulation of the contribution of both inertial and aerodynamic force... more A two-dimensional numerical simulation of the contribution of both inertial and aerodynamic forces on the blade loads of a Vertical-Axis Wind Turbine (VAWT) is presented. After describing the computational model and the relative validation procedure, a complete campaign of simulations -based on full RANS unsteady calculations -is proposed for a three-bladed rotor architecture characterized by a NACA 0021 airfoil. For each analyzed angular velocity, the combined effect of pressure and viscous forces acting on every rotor blade are compared to the corresponding centrifugal forces, due to the revolution of the turbine, thus achieving a preliminary estimation of the correlation between overall rotor efficiency and structural blade loads.
Reynolds averaged Navier-Stokes equations and Realizable k model were used in this paper, and the... more Reynolds averaged Navier-Stokes equations and Realizable k model were used in this paper, and the two dimensional unsteady flow field of the vertical axis wind turbine was simulated numerically at different wind velocity. The calculation results showed that the velocity in the region of wind turbine s rotation was much larger than the air flow of the upstream. The length of the wind turbine s downstream wake dispersion region was increased with the increase of the wind velocity. There is a much larger value of the eddy in the rear region of the wind turbine s rotational blades. And eddy existed in the downstream region of the wind turbine, and the larger velocity of cross flow, the larger value of the downstream flow s eddy. When the rotational speed was constant, with the increase in wind velocity, the variation of the s total torque coefficient tended to smooth. The calculation results pointed out the direction for the follow-up study.
As the energy crisis is getting severe in the world it will be important to investigate alternati... more As the energy crisis is getting severe in the world it will be important to investigate alternative methods of generating power in ways different than, fossil fuels. In fact, one of the biggest sources of energy is all around us all of the time, the wind. Currently, horizontal axis wind turbines (HAWT) dominate the wind energy market due to their large size and high power generation characteristics. However, vertical axis wind turbines (VAWT) are capable of producing a lot of power, and offer many advantages for small-scale and domestic applications. One drawback of DARRIEUS type VAWT is their inability to reliably selfstart at low tip speed ratio. The details of different configurations and performance evaluation techniques along with the major findings of researchers on vertical axis wind turbines are reviewed in this paper. The main purpose of the study described here is to investigate effect of different design parameter on performance evaluation of VAWT.
The control of a wind turbine to the mean wind speed in a gusty wind results in very poor perform... more The control of a wind turbine to the mean wind speed in a gusty wind results in very poor performance. Fluctuations in wind speed with time constants shorter than the response time of a wind turbine results in operation away from optimum design conditions.
Increasing demand for energy in recent years has seen a rise in development of alternative energy... more Increasing demand for energy in recent years has seen a rise in development of alternative energy sources. Wind being one of the most abundant and easily available sources is an excellent alternative to conventional energy sources.
The paper aims to investigate the performance of the high aspect ratio vertical axis wind turbine... more The paper aims to investigate the performance of the high aspect ratio vertical axis wind turbine with numerical method and to present some experimental results. Aerodynamics with numerical method is a major prospect of the investigation. Computational fluid dynamic software, ANSYS CFX, is employed to analyze drag force generated from the influence of blade shape. Two types of turbine blades have been investigated with aerodynamics prospects, namely shape-design model and mechanism model. Power coefficient of each models are calculated and compared. Turning force to reverse force ratio has been used to compare different shapes of the turbine blade. It has been found that the mechanism model, with power coefficient of 16.2 per cent, offers better capability of harnessing wind energy than shape-design model.
This case study investigates the generator of a large offshore Vertical Axis Wind Turbine (VAWT).... more This case study investigates the generator of a large offshore Vertical Axis Wind Turbine (VAWT). In particular this case study focuses on the effect of the inherent cyclic torque loading of the VAWT on the generator in terms of the costs and losses experienced. A spectrum of torque control strategies were created based on the ratio q of the allowed electrical torque variation to the mechanical torque variation. Equations relating the copper and iron losses of the generator to this q factor were established and investigated for a test turbine. In addition the relationship between the allowed variation in electrical torque and the cost of the active materials of the generator was explored.
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Papers by Mostafa Rashed