H-type Vertical Axis Wind Turbine Research Articles

Optimal Design of Anti-Icing Blunt Trailing-Edge Wind Wheel for H-Type Vertical Axis Wind Turbine Under Operating Conditions

Abstract A novel optimization method is developed for the design of an anti-icing blunt trailing-edge wind wheel of H-type vertical axis wind turbine (VAWT) based on the quasi-steady-state icing. The parametric expression of the airfoil is given using the mean camber and thickness functions, the blunt trailing-edge is constructed by the rotation and zoom of coordinates, and then through the aerodynamic design theory, the geometry control equations of the blunt trailing-edge wind wheel are established. The icing process using Solution and Icing modules is repeated at equal interval azimuths to obtain the ice on the wind wheel per revolution. The optimization model is solved using particle swarm optimization (PSO) algorithm integrated with computational fluid dynamics (CFD) method to maximize the wind energy utilization in both ice-free and icing conditions. Significant improvements are realized for flow and aerodynamic characteristics, confirming that the optimization method provides important guidance for an anti-icing design of VAWT blades.

Aerodynamic performance optimization of vertical axis wind turbine with straight blades based on synergic control of pitch and flap

Low power efficiency is a critical reason that restricts the potential application of the vertical axis wind turbine (VAWT) in offshore engineering. Hence, efficiency enhancement is an essential topic for the VAWT design. This paper attempts to propose an improved active control strategy and a novel blade structure with a trailing-edge flap for H-type VAWT to improve the power outputs at different tip speed ratios (TSRs). The orthogonal experiment design (OED) method was applied to optimize the motion of pitch and flap at low and moderate TSRs. Subsequently, the output characteristics, including the coefficients of power, torque, tangential force, and thrust of the optimized pitch-flap (P-F) model and three other models, namely the base model, the pitch-only (P-O) model, and the flap-only (F-O) model, were compared. Besides, the flow structures and static pressure distribution on the blade surface were studied to reveal the mechanism of power increase. It was found that the synergic motion of pitch and flap could effectively suppress the flow separation and delay the dynamic stall around blade. The result indicated that enhancement of the P-F model in torque coefficient was over 130% and 60% at low and moderate TSRs compared to the base model. In addition, the synergic motion of pitch and flap was found able to reduce the load fluctuation of the VAWT. The improved active control strategy and the blade structure with a trailing-edge flap may be helpful for the potential application of the H-type VAWT in offshore engineering.

Power enhancement of vertical axis wind turbine using optimum trapped vortex cavity

Vertical Axis Wind Turbine (VAWT) blades experience stall conditions at lower tip speed ratios during rotation, resulting in inefficient power performance. The power performance can be augmented by improving the blade's aerodynamic efficiency using active or/and passive flow control mechanisms. In this research, the power performance of 2-D H-type VAWT is enhanced by employing an optimum cavity on the suction side of the NACA 0018 blade airfoil. The optimum cavity shape was found using the Genetic Algorithm coupled with the Gaussian Process Regression (GPR) model at an airfoil static stall angle of attack in an isolated environment to reduce the computational cost of the optimization process. Two GPR models were employed to predict lift and drag coefficients, while the lift-to-drag ratio was used as an objective function in the optimization algorithm. 80 CFD runs were utilized for initial training and testing of the models, which reduced computational effort by 97% compared to a pure CFD-based optimization approach. The aerodynamic efficiency of the optimum cavity shape predicted by GPR models was also confirmed by CFD simulation, which showed only a 0.5% difference. For an airfoil with an optimum cavity, the aerodynamic efficiency was consistent at lower angles of attack. However, a significant rise of up to 31.8% was observed in the near stall region between 12° to 16° angle of attack in comparison to clean airfoil. The optimum cavity on baseline VAWT blades enhanced power performance by 63.8% at a TSR of 1.5. Moreover, at TSRs of 2, 2.5, 3, and 3.5, the enhancement in power performance was achieved by 34.4%, 22.2%, 16.1%, and 3.2%, respectively. This demonstrates the potential of employing an optimum cavity on the suction side for performance augmentation without applying the suction and a cost-effective solution by conducting optimization in an isolated environment.

Experimental and numerical study of the wake deflections of scaled vertical axis wind turbine models

Wake steering of vertical axis wind turbines (VAWTs) is investigated experimentally and numerically via stereoscopic particle image velocimetry and Reynolds averaged Navier-Stokes simulations. Three different blade pitch angles (-10°, 0°, 10°) of straight H-type VAWTs are adopted to deflect and deform the wake. The experimental results confirm the efficacy of blade pitching on the wake steering, and validate the simulation for both moderate and significant wake deflections. The simulation is then extended to full-scale VAWTs, exploring the wake deflection effects on the power performance of VAWT arrays. The effects of inter-turbine distances and pitching configurations are considered. With the upwind VAWT deflecting the wake, the overall power coefficient is increased by 41%.

Investigation of energy dissipation of an H-type vertical axis wind turbine based on entropy production theory

In vertical axis wind turbine (VAWT) research, amount studies have been conducted about the flow field around the blades, but the effect of blade tip vortex was not revealed clearly. The present study emphasized on the effect of blade tip vortex on energy loss in wake region and employed entropy production theory to determine where and how energy loss generates quantitatively. The numerical simulation was conducted for the VAWTs versus various tip speed ratio (TSR) conditions, and the numerical results were analyzed by entropy production method. The energy loss calculated by entropy production theory in VAWTs flows increases with TSR increasing. The distribution of entropy production rate (EPR) in wake region was asymmetrical due to the influence of blade tip vortex diffusion downstream and two fluctuation peaks appeared on EPR curves. The energy loss coefficient was defined to represent the energy deficit and kinetic energy recovery in wake region quantitatively. Generally, the energy loss coefficient was reduced to 0.1 between 8D to 9D in wake region and was equal to 0.1051 at x = 8D under optimal condition TSR = 2.19. The present study can guide configuration optimization of VAWTs to improve wind energy utilization and revenue of wind farms.

Key factors influencing urban wind energy: A case study from the Dominican Republic

This article presents the urban wind potential that exists in the provinces of the Dominican Republic through free access data provided by numerical weather prediction and geographical information systems. Then, a hybrid Strengths, Weaknesses, Opportunities, and Threats (SWOT) – Analytic Hierarchy Process (AHP) analysis was conducted to qualitatively determine the factors that influence urban wind energy, and the weighting of these through expert judgments, quantifying the prioritized factors. The results show that the average consolidated urban wind speed is 3.66 m/s at 10 m height, and the predominant direction is 86°. Adopting the parameters of the Weibull distribution, an Annual Energy Production (AEP) of 1,145 kWh/y is estimated for one small wind turbine. Assuming that ten 2-blade Darrieus H-type vertical axis wind turbines are installed in each province, the global AEP is 423,936 kWh/y. Applying the hybrid analysis with the combination of the factors, the results indicate that the strengths and opportunities represent 0.693 and the weaknesses and threats are 0.307. The most important SWOT factors of each category were i) low emission of greenhouse gasses (internal), ii) low energy sale price of surplus energy to the grid (internal), iii) use of public policies (external) and iv) bureaucracy and slow processes in public companies related to permits (external).

Wind energy potential assessment of selected locations at two major cities in the Dominican Republic, toward energy matrix decarbonization, with resilience approach

Climate changes pose big challenges to scientists, engineers, and decision makers to provide sustainable energy services to cities. Innovative energy solutions are required to fulfill the growing energy demand in a sustainable and resilient way, especially in developing countries. The implementation of small-scale energy systems integrated in urban sites such as wind and solar are a promising technological approach, in this direction urban wind energy can be a suitable resource. A preliminary assessment of urban wind energy is needed by turbine developers, investors, and decision makers. The present work aims to present an assessment of wind energy potential of selected locations at two major cities in the Dominican Republic, for this purpose was developed a robust framework to provide an assessment of the wind energy potential in a tropical area for roof-mounted turbines. The framework is based on six main steps: (1) site selection, (2) resource prospecting/analysis, (3) turbine selection, (4) estimation of currently produced energy, (5) environmental evaluation and (6) resilience assessment. The resilience metrics have been adopted to novel assess three scenarios of resilience in tropical areas. The methodology was applied in San Cristóbal and Santo Domingo, two major cities in the Dominican Republic. The urban wind energy potential was assessed considering the installation of 1,075 small two-blade Darrieus H-type Vertical Axis Wind Turbines (VAWTs) on the roofs of 275 high-rise buildings, with annual energy production of 317 MWh, represented a potential CO2 emissions reduction of 197 Ton/yr.

Transient analysis of H-type Vertical Axis Wind Turbines using CFD

In this study, the effect of various parameters on the start-up and transient behavior of Darrieus straight-bladed Vertical Axis Wind Turbine (VAWT) was analyzed. Airfoil profile, angle-of-attack, and chord length were varied, yielding two optimal turbines, one for transient and another for steady performance. This optimization revealed that the chord length (solidity) has the most significant impact on the performance of the turbine undergoing both transient and steady operations. An examination of the contribution of drag and lift forces to the startup of these two optimized turbines shows that the drag has a positive contribution to the performance of the transient optimized turbine especially at high TSRs. The performance of the optimized turbines when subject to four different wind profiles: a real wind profile, and three distinct sinusoidal profiles was also assessed. At low average wind speeds, a high frequency of the incoming wind is favorable for allowing both optimized turbines to produce more power. The rotor behavior under dynamic loads was also investigated, demonstrating that the transient optimized turbine is more responsive and therefore easier to control. In addition, minimizing the inertia of the steady-optimized turbine significantly improves its startup characteristics, making it superior to its steady-optimized counterpart.

Investigation of aerodynamic forces and flow field of an H-type vertical axis wind turbine based on bionic airfoil

This paper investigates the effect of bionic airfoil on the aerodynamic characteristic and flow field of an H-type vertical axis wind turbine (VAWT). The pressure acting on the blade surface and flow field around the blade were predicted at different tip speed ratios (TSRs) and the angles of attack were predicted by numerical simulation. As a result, it was showed that the maximum value of lift force coefficient was 0.723 for baseline airfoil at the angle of attack 12° and was 0.743 for bionic airfoil at the angle of attack 14°. When the angle of attack was equal or greater than 14°, the static bionic airfoil showed better lift characteristic. Moreover, the maximum value of power coefficient occurred at TSR = 2.58 for the simulation, but the maximum value of torque coefficient was identified at TSR = 2.19. Meanwhile, the growth rates of the power coefficient were 7.02% at TSR = 1.38, 7.35% at TSR = 2.19, and 3.42% at TSR = 2.58 for simulation between baseline blades and bionic blades. The power performance of VAWT improved in dynamic stall for bionic airfoil by delaying stall on the blade's surface and promoting the laminar-to-turbulent transition to improve the power performance of wind turbine at the low TSRs for the mainstream wind velocity of 8.0 m/s. The research results were helpful to predict the performance of VAWTs under various wind environments and to improve the aerodynamic performance of VAWTs.

Aerodynamic shape optimization of H-VAWT blade airfoils considering a wide range of angles of attack

Abstract The current H-type vertical axis wind turbine (VAWT) airfoils are from horizontal axis wind turbine airfoils or symmetry airfoils that are designed at one angle of attack (such as α = 6°) rather than different angles of attack. As a consequence, it cannot, to a certain extent, increase wind power efficiency. Therefore, an optimal method of H-type VAWT blade airfoils in different ranges of angles of attack is presented. It can be expressed by airfoil integrated function. Then, an optimized mathematical model in which the objective function is the average of tangential force coefficients is established. The particle swarm optimization algorithm coupled with RFOIL program is introduced to optimize the H-type VAWT airfoil profiles with high aerodynamic performance. The optimized results show that the new HVAWT-00153 airfoil is more suitable to VAWTs than the other two new airfoils and NACA-0015 airfoil. Besides, by using computational fluid dynamics technology, the superiority of HVAWT-00153 airfoil over NCAC-0015 airfoil is reviewed. The results indicate that the H-type VAWT with new HVAWT-00153 airfoils could exhibit larger torque coefficients and higher power coefficients than that of the original H-type VAWT with NACA-0015 airfoils. The maximum power coefficient can reach 0.362, increased by 8.45% compared with that of the original one. This study has a good guidance to how to design the H-type VAWT airfoils with high wind energy power.

Health Monitoring and Diagnosis System for a Small H-Type Darrieus Vertical-Axis Wind Turbine

As the wind power market grows rapidly, the importance of technology for real-time monitoring and diagnosis of wind turbines is increasing. However, most of the developed technologies and research mainly focus on large horizontal-axis wind turbines, and research conducted on small- and medium-sized wind turbines is rare. In this study, a novel low-cost and real-time health monitoring and diagnosis system for the small H-type Darrieus vertical axis wind turbine is proposed. Turbine operating conditions were classified into parked/idle and power production. In the case of the power production condition, abnormality diagnosis was performed using key monitoring parameters, including vibration, fundamental frequency, the bending stress of the tower and generator vibration. The turbine abnormalities were diagnosed in two stages by applying the alert and alarm limits, determined by referring to international standards and material properties and the long-term measurement data together.

Wind Tunnel Experiments and Numerical Study on Performance Characteristics of an H-type Vertical Axis Wind Turbine in the Spanwise Direction

The aerodynamic forces and vortex characteristics of an H-type Vertical Axis Wind Turbine (VAWT) become complicated because of dynamic stall, particularly in the three-dimensional impact on the blade spanwise direction. This study focused on the evaluation of the aerodynamic performance and vortex characteristics of an H-type VAWT in the spanwise direction by numerical simulations and wind tunnel experiments. Pressure acting on the blade surface was obtained from multiport pressure measurement devices by wind tunnel. Meanwhile, the vortex field around different blade sections was investigated through numerical simulations. The stall behavior was analysed by comparing the results of numerical simulations and experiments. As a result, the tangential force of single blade was mainly contributed at the chordwise position of x/c≤0.4c and the power of single blade was mainly contributed at the azimuthal angle range of 60°≤θ≤150° in the blade section position region of 0≤z/(H/2)≤0.7. At the section position of z/(H/2)=0.5, the initial flow separation was found at the suction side and progressed forward to the leading edge. With the increase of the tip speed ratios, the decreasing position of the averaged local power coefficient of each section was closer to the middle section of z/(H/2)=0, and the attenuation speed became faster. The power coefficient reductions at the blade section position of z/(H/2)=0.9 were 38.29%, 46.78% and 56.42% when the tip speed ratios were 1.38, 2.19 and 2.58, respectively. The results of this study provided a better understanding of the development of the performance characteristics and vortex characteristics of H-type VAWT.

Structural optimization of H-type VAWT blade under fluid-structure interaction conditions

To reduce the errors caused by the rigid body hypothesis in the aerodynamics-structure coupling calculation and improve the structural performance, an optimum structure design with the consideration of the fluid-structure interaction are performed for the H-type vertical axis wind turbine (VAWT) blade. Based on the ANSYS Workbench platform, the geometric model, computational domain and grids of the wind wheel are constructed, the turbulence model, boundary conditions and composite material layers are set up, and the fluid and solid domains are solved in a coupled way. The single-objective structural optimization model in which the thicknesses of glass clothes, foam and gel coat, and the positions of two webs are taken as design variables is solved using the response surface optimization method to minimize the wind wheel mass. The frequencies and vibration modes of original and optimized blades with and without pre-stress and the transient characteristics of wind wheels in different wind speeds are investigated. The results indicate that after the blade optimization, the first-order frequency and critical speed become larger and other frequencies reduce for the static, single pre-stress and multiple pre-stresses states, and the maximum displacement, stress and strain of the wind wheel decrease under rated and extreme wind speeds, confirming significant performance improvements. The research provides useful guidance for the integrated design of structure and aerodynamics of wind turbine blades.

Aerodynamic performance improvements of a vertical axis wind turbine by leading-edge protuberance

A detailed numerical study has been carried out to investigate the effects of leadingedge protuberance as a novel flow-separation control-technique for vertical-axis-windturbine (VAWT). The aerodynamic performance of a stationary protuberanced blade and an associated H-type Darrieus VAWT made of three protuberanced blades were investigated using unsteady Reynolds-Averaged-Navier-Stokes (URANS) and Implicit Large Eddy Simulation (ILES) methods. The current study involves a comprehensive set of five different types of sinusoidal leading-edge protuberances with three different wavelengths and amplitudes. It is found that this passive flow-control-method can favourably change lift and drag at stall and post-stall regions, which is of high importance for VAWTs. Static stall variation can be changed from leading-edge-stall type to trailing-edge-stall type. This is attributed to a “bi-periodic” phenomenon over the blade suction side and a reduced turbulence kinetic-energy production. Protuberance amplitude was found to be more important than the wavelength in improving aerodynamic performance. Of all the tested cases, the protuberance with amplitude of 1% chord-length (c) and wavelength of 2.5%c behaves the best. The leading-edge protuberance can significantly increase VAWT power-coefficient at low tip-speed-ratios, which are dominated by post-stall conditions. The dynamic stall was delayed and the coherent spanwise wavy flow-structures on the blade suction-side were observed.

Guidelines for the computational domain size on an urban-scale VAWT

Focusing on the H-type vertical axis wind turbines (VAWTs) widely used in urban, the SST k - ω turbulence model was selected to establish a two-dimensional Computational Fluid Dynamics (CFD) model, the moment coefficient (Cm), and power coefficient (Cp) was taken as the evaluation indicators. The CFD model was used in different domain sizes. The simulation results under the sizes were used to investigate the effect of the computational domain size on the numerical simulation results of the aerodynamic performance of the VAWT. Furthermore, a distance from the turbine center to the domain inlet and outlet of 10D (D: diameter of the turbine) each, a domain width of 10D and a diameter of the rotating core of 1.5D are found to be safe choices to minimize the effects of blockage and uncertainty in the boundary conditions on the results. It provides a reference for the selection of the domain size when CFD simulation is implemented in a vertical axis turbine to get its prediction of the performance in the future accurately.

Free and Forced Vibration Analysis of H-type and Hybrid Vertical-Axis Wind Turbines

Vertical-axis wind turbines (VAWTs) are compact and efficient and have become increasingly popular for wind energy harvesting. This paper mainly focuses on free and forced vibration analysis of two different types of VAWTs, i.e., an H-type VAWT and a new hybrid VAWT. The H-type VAWT has a lower cost, while the hybrid VAWT has a better self-starting capability at a low wind velocity. Both of them can be used for wind energy harvesting. By using the assumed modes method, the two VAWTs are simplified by a single degree-of-freedom (SDOF) model. By utilizing the method of structural mechanics, a multi-degree-of-freedom (MDOF) model is developed for the two VAWTs and the turbines in them are reasonably simplified. Natural frequency analyses for the SDOF and MDOF models of the two VAWTs are conducted. A beam element model (BEM) of the two VAWTs is created to calculate their natural frequencies and mode shapes and to verify natural frequency results from the SDOF and MDOF models. By using the BEM of the two VAWTs, their amplitude-frequency responses are obtained from harmonic response analysis. To analyze forced vibrations of the two VAWTs, aerodynamic loads on the two VAWTs are obtained from computational fluid dynamics (CFD) simulation. By using solid element models of the two VAWTs, forced transient responses of the two VAWTs are calculated by using the aerodynamic loads from CFD simulation. Steady-state forced response amplitudes of the 1 m-mast hybrid VAWT are 23.8% and 20.5% smaller in X- and Y-directions than those of the 1 m-mast H-type VAWT, respectively. Frequency contents of the aerodynamic loads from CFD simulation are calculated, which confirm that they are periodic, and the power efficiency of the H-type VAWT is about 2.6% higher that of the hybrid VAWT.

Towards optimal layout design of vertical-axis wind-turbine farms: Double rotor arrangements

Designing an optimal wind farm layout requires fundamental knowledge of the interaction of wind turbines in an arrangement. In this paper, extensive high-fidelity CFD simulations are performed to investigate the influence of relative spacing, i.e., distance (R) and angle (Φ), in double rotor arrangements of co-rotating Darrieus H-type vertical axis wind turbines (VAWTs) on their aerodynamic performance. The relative spacing varies within 1.25d ≤ R ≤ 10d (d: turbine diameter) and −90° ≤ Φ ≤ +90°. The turbines operate at their optimal tip speed ratio. The analysis is focused on the individual and overall power performance of the turbines and their aerodynamics. Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations, validated with experiments, are employed. It is found that an optimal region exists in which a higher overall power coefficient (CPoverall) compared to the CP of an isolated solo rotor (CPSolo) can be achieved. This region corresponds to compact rotor arrangements, i.e. R/d ≤ 3d with Φ ≥ +45° and Φ ≤ −45°, yielding a maximum 1.8% increment in CPoverall/CPSolo at R/d = 1.25 and Φ = +75°. Detailed flow analysis reveals that in the optimal spacing, a narrow passage between the two rotors is formed within which the flow accelerates, forming a high-velocity region. The downstream turbine benefits from its blade(s) passing through this region and consequently yields higher CP values. The findings highlight the high potential for compact VAWT farms with high power density and support the optimal layout design of VAWT farms.

A numerical investigation to analyze effect of turbulence and ground clearance on the performance of a roof top vertical–axis wind turbine

Recent attempts to discover energy–efficient and cost–effective power generation systems unleash tremendous capabilities of urban rooftops vertical–axis wind turbines (VAWT). Their advantages of Omni–directionality, low noise and less maintenance cost allow direct integration to urban neighborhood having unstable wind conditions. Despite continuous effort to investigate performance under a range of operating conditions, aspects such as Turbulent Intensity (TI) and ground clearance remain relatively less explored. Such effects originate either due to sharp topographical variations or placement of the turbine blades in proximity to the ground. In the present work, we perform a parametric study to quantify the performance of VAWT under various levels of TI and ground clearance. We conduct high fidelity Computational Fluid Dynamics (CFD) simulations using ANSYS Fluent and k−ε turbulence model. The H-type VAWT is employed having rated power of 1.5kW, diameter (D)of 2.5mchord length (c) of 0.2m and operates at prescribed wind speed (U0)of 12.0m/sand Tip Speed Ratio (TSR) of 1.5–4.5. We determine the performance of turbine under four levels of TI i.e., 0%, 5%, 15%25%at five ground clearance levels of 1.0c,2.5c,4.0c,7.5cand 10.0c. The results show a performance loss of 30.10%, 20.65%, 10.65% at turbine clearance heights of 1.0c,2.5c, 4.0c respectively. The height of 7.5c yield higher and more consistent performance under given operating conditions. The results for induced turbulence identify a decrease in the performance up to 45.42% corresponding to 25%TI level.

Torsional Aeroelasticity of a Flexible VAWT Blade using a Combined Aerodynamic Method by Considering Post-stall and Local Reynolds Regime

The present research investigates the torsional aeroelasticity of the blade of an H-type vertical axis wind turbine subject to stall and post-stall conditions in various Reynolds regimes, which is experienced by the blade in a full revolution. In order to simulate the aerodynamics, a new model based on a combination of the Double Multi Streamtubes (DMST) model and the nonlinear multi-criteria Cl-a equations, which is depended on the local Reynolds number of the flow, has been proposed. The results indicate that using of multi-criteria function dependent on the Reynolds number for the Cl-a curve has improved the prediction of the torsional behavior of the blade in azimuthal rotation of the blade compared to using single-criterion functions and linear aerodynamics. The blade’s aeroelastic torsion has been studied for various TSR values.

Aerodynamic investigation of the start-up process of H-type vertical axis wind turbines using CFD

In this study, a CFD start-up model has been built after conducting the sensitivity studies to evaluate the self-starting behaviour of the H-type vertical axis wind turbines (VAWTs). The self-starting behaviour of a well-investigated VAWT is used for the model validation, and then the details of aerodynamics of the start-up process have been examined. Finally, the effect of the moment of inertia and the blade number on the aerodynamic behaviour of the self-starting and power performance of the H-type VAWT are analysed. It has been found that in the critical region, where TSR<1, the contribution of the drag to the torque generation plays a significant role in the second and third quarters of the rotor revolution, where the azimuthal position varies between 100° and 253°. The results also show that increasing the turbine inertia did not show a noticeable effect on the start-up behaviour of the turbine and final rotational speed. However, an increase in the instantaneous turbine power during the start-up process after the optimum TSR is observed with decreasing the turbine inertia. The current findings also show that an increase in the blade number makes the turbine easier to start-up; however, this may reduce the turbine power coefficient.