Performance analysis of vertical axis wind turbines by varying tip-speed ratio using open source CFD solver

The need for energy and electricity has been increasing globally, and this means more power is required from the power plants. Power plants, however, will then continue harming the earth because of the greenhouse gasses produced while generating energies that contribute to global warming. Using renewable sources to produce clean energies is one of the sustainable methods to deal with such challenges. Wind energy is one of the renewable sources, which is accessible anywhere on earth, creating green energy. Wind turbines are mainly categorized into Horizontal Axis Wind Turbines (HAWT) and Vertical Axis Wind Turbines (VAWT). This paper firstly presents a general comparison between the HAWTs and VAWTs. Then, it presents mathematical modelling for the aerodynamic factors of HAWT and Darrieus VAWT to assist the researchers to understand some key design aspects of wind turbines, such as lift/drag ratio, tip speed ratio, power coefficient, and torque coefficient. Also, this paper presents a review of the aerodynamic performance of the recent VAWT designs to help researchers to identify and choose the best model among the Savonius and Darrieus rotors for further development or designing a new model at different wind conditions. This comparison review shows that for a large scale HAWT upwind 3 bladed wind turbines are the most optimum. The helical Savonius rotors perform better by having positive torque coefficient at all azimuth angles. Moreover, helical Darrieus was found to produce lesser noise and suitable for conventional areas. hybrid Savonius-Darrieus rotors can solve the self-starting challenge of the VAWTs, and they are suitable at low wind speeds. At last, this review shows some of the recent hybrid Savonius-Darrieus rotors which would help to solve the low efficiency of Savonius rotor and self-starting challenge of Darrieus rotors.

This study characterises the performance of the Savonius type vertical axis wind turbine (VAWT). The performance of the Savonius type VAWT can be characterised by power and coefficient of power. The main parameter considered for analysing the Savonius-type VAWT is the tip speed ratio (TSR). The mesh independency test and time independency test are carried out, in which the medium mesh and three degree of time step for rotation are selected. The Savonius wind turbine is analysed at various TSR ranging from 0.2 to5.0, in which TSR is 4.4, the performance of the turbine is high. Considering 4.4 TSR as the optimum one, the analysis of the Savonius type VAWT is carried out under various wind speed ranging from 1 to 10 m/s. From the analysis, the validation between numerical analysis and theoretical analysis is carried out and the efficiency of the Savonius type VAWT is increased to 50%.

The demand for wind turbines has increased ever since fossil fuels showed signs of quick depletion. Among wind turbines, Vertical Axis Wind Turbine (VAWT) is compact, produces less noise, is omnidirectional, resilient to turbulent flow, and is easy to maintain. The power generated by a VAWT is a function of a non-dimensional geometric parameter known as solidity (s), which is a function of turbine diameter (D), blade chord (c) and the number of blades (n). The present work analyses the impact of solidity (0.12 and 0.18) as a complete non-dimensional parameter on wind turbine performance. Each parameter of solidity is varied, keeping any one of the parameters constant and numerically studied for its performance across a range of tip speed ratios (TSR). For each solidity, six different combinations of VAWT geometric parameters were analyzed. In all the cases, the chord Reynolds number is kept constant. CFD simulation was performed on the Darrieus H-type (NACA0018 airfoil) VAWT. Two dimensional (2D) computational domains are used to study the effect on the turbine’s performance as the solidity studied is less than 0.4. Unsteady Reynolds-Averaged Navier-strokes (URANS) equation is used to solve the CFD model using ANSYS Fluent 19.1 with 4-equation transition SST k-ω for turbulence modelling. The comprehensive study of the turbine performance keeping the turbine operation within a constant Re number range shows the Coefficient of Performance (Cp) overlaps for a given solidity.

Research of asymmetric airfoil on aerodynamic characteristics of vertical axis wind turbines

The application of the Darrieus rotors in regions with lower wind potentials is one of the challenging issues in the operation of this type of vertical axis wind turbine (VAWT). To overcome this problem, various combinations of Darrieus and Savonius rotors, called the hybrid rotor, are proposed, which is one of the attractive subjects among wind turbine researchers. Using the computational fluid dynamics technique (CFD), this study investigates a new combination between the Savonius and Darrieus rotors at which a two-bladed Bach-type rotor is attached inside a two-bladed Darrieus rotor made by NACA 0018. In this way, various attachment angles (α) between the internal and external rotors such as 0°, 45°, and 90° are studied to find the optimal case. Computations are performed for various tip speed ratios (TSR) such as 1.5, 2.5, and 3.5, and free-wind speeds (U∞) of 5 and 10 m/s. The obtained results revealed that the application of a hybrid wind turbine is more beneficial under lower TSR and U∞ values. Additionally, it is demonstrated that the case with α = 90° is the optimal case in TSR = 1.5 and 2.5 providing a maximum 21.43% improvement in comparison to the Darrieus rotor for TSR = 1.5 and U∞ = 5 m/s.

Increasing environmental concerns have led to a demand for more environmentally friendly energy options. Worldwide, wind energy is one of a clean, renewable source of green electricity. Fossil fuel is one of our most important sources of energy and its quantities are decreasing. However, wind is a renewable resource that can as stand by source with fuel. Wind turbines are used to harness the wind to generate energy. Vertical axis wind turbines (VAWTs) are suitable for use in built sites because to their outstanding features, attractiveness, low noise, and safety. To achieve these objectives, vertical axis wind turbines with multiple blades (blades are made from polyvinyl chloride (PVC) material) have been designed, manufactured and studied experimentally to investigate its performance. Turbine’s blade is a half cylinder in its shape. The blades rotational speed of the blades, the resulted torque (T), and generated power (P) of each configuration of the suggested turbine were determined for different wind speeds (1.5m/s, 2.5m/s, and 3m/s) and rotor radius of (30cm, 40cm, and50cm), respectively. The graphical relation between coefficient of power (Cp) and the tip speed ratio (TSR) and between coefficient of power (Cp) and angles of the blades were constructed. It was noted that performance of wind turbine is largely depends on wind speed, blade locations, and blade angle. The maximum value of the power coefficients (Cp = 13.056%) is noticed at 40cm and 1.5 m/s for blade radius and wind speed, respectively, specifically at TSR=1.3 and 450 blade angle. The maximum values of the Cp for all values of the effective parameters are noticed at 450 blade angle. In addition, higher values of Cp are achieved at the lower wind speeds and high blade radius, and that corresponds to higher TSR. Finally, VAWT is able to generate electricity for local use even at low wind speeds.

Airfoil optimization to improve power performance of a high-solidity vertical axis wind turbine at a moderate tip speed ratio

Modern designs for straight-bladed vertical axis wind turbines (VAWTs) feature smaller individual footprints than conventional horizontal axis wind turbines (HAWTs), allowing closer spacing of turbines and potentially greater power extraction for the same wind farm footprint. However, the wakes of up-stream turbines could persist far enough to affect the performance of closely-spaced downstream turbines. In order to optimize the inter-turbine spacing and to investigate the potential for constructive aerodynamic interactions, the complex dynamics of VAWT wakes should be understood. The full three-component mean velocity field around and downstream of a scaled model of a rotating VAWT has been measured by Magnetic Resonance Velocimetry (MRV). The model turbine has an aspect ratio (height/diameter) of 1, and was operated in a water facility at subscale but still turbulent Reynolds number of 11,600 based on the turbine diameter. The main flow features including recirculation bubble sizes and strong vortex structures are believed to be representative of flow at full scale Reynolds number. To have kinematic similarity with a power-producing turbine, the model turbine was externally driven. Measurements were taken with the turbine stationary and while driven at tip speed ratios (TSRs) of 1.25 and 2.5, realistic values for VAWTs in operation. The MRV measurement produced three-dimensional velocity data with a resolution of 1/50 of the turbine diameter in all three directions. The flow is shown to be highly three dimensional and asymmetric for the entirety of the investigated region (up to 7 diameters downstream of the turbine). The higher TSR produced greater velocity defect and asymmetry in the near wake behind the turbine, but also showed faster wake recovery than the slower TSR and stationary cases. Wake recovery is affected by a counter-rotating vortex pair generated at the upwind-turning side of the turbine, which mixes faster fluid from the freestream in with the wake. The strength of vortices is shown to increase with TSR.

In recent decades, wind turbines have emerged as substantial renewable energy technologies, particularly for offshore applications. However, the utilisation of conventional wind turbine in regions characterised by a low wind speed profile, such as Malaysia, remains limited. To address this gap, this study develops an unconventional small-scale Vertical Axis Wind Turbine (VAWT) provision for offshore application in Malaysia’s low wind speed regions. The study commenced with a wind feasibility analysis which aimed to determine the viable range of offshore wind speeds prior conducting wind tunnel tests. The VAWT model was designed using SolidWorks software, fabricated using a 3D printer and tested in the National Defence University of Malaysia (UPNM) wind tunnel lab facilities. Through a systematic analysis and optimisation of blade diameters, stages and angles using Taguchi method, this study aimed to enhance the wind turbine performance in terms of power coefficient (Cp) and tip speed ratio. The result highlighted the pivotal role of blade diameter and the number of stages as a key design factor for VAWT, with the optimal configuration of blade diameter of 16 cm, a single stage and Angle of Attack (AoA) of 7°, resulted in a Cp value of 0.622. It is important to note that this Cp value exceeds the typical wind turbine power coefficient benchmarks, which range from 0.3 to 0.45, indicating that the optimised design offers a higher-than-average efficiency for small-scale VAWTs. Additionally, variations in AoA were found to be the least significant design factor, as all models demonstrated peak Cp values corresponding to wind speeds. Although tested in a controlled wind tunnel environment, these results suggest that the optimum design could perform efficiently under Malaysia's real-world offshore conditions, where wind speeds are typically low. This study provides key design considerations for small-scale VAWTs in low wind profile regions, contributing to the sustainable development of wind energy in Malaysia.

The Design and Flow Simulation of a Power-augmented Shroud for Urban Wind Turbine System

Wind energy has emerged as one of the fastest-growing renewable energy sources, with horizontal axis wind turbines (HAWTs) predominantly deployed in large-scale applications.However, their effectiveness in urban environments is limited due to fluctuating wind patterns and space constraints.In contrast, vertical axis wind turbines (VAWTs) offer advantages such as compact design, low noise levels, and stable performance under low-speed and turbulent wind conditions, making them more suitable for urban settings.This review examines the performance characteristics of key VAWT configurations, including lift-based Darrieus turbines, drag-based Savonius turbines, and hybrid designs.Typical power coefficients (Cp) for these designs are approximately 0.4 for Darrieus, 0.15-0.2for Savonius, and 0.3-0.35 for hybrid models.Optimal operation is generally achieved at a tip speed ratio (TSR) of 0.45, corresponding to a maximum Cp of around 0.306 and a torque coefficient of 0.68.The review also identifies critical design and operational parameters influencing turbine performance.Finally, it highlights the need for continued research to enhance efficiency, reliability, and integration of VAWTs into future urban energy systems.

Considerable improvements in the aerodynamic performance of a vertical axis wind turbine (VAWT) can be achieved by integrating computational fluid dynamics (CFD) simulation and wind tunnel investigation in their design improvement. With the growing demand for energy worldwide, conventional sources are becoming more scarce and expensive. Wind is among the most popular and fastest growing sources of alternative energy in the world. It is an inexhaustible, indigenous resource, pollution-free, and available almost any time of the day, especially in coastal regions. Industry experts predict that, with proper development, wind energy could provide 20% of the nation’s energy needs. Vertical axis wind turbines (VAWTs) may be as efficient and practical as, and simpler, and significantly cheaper to build and maintain than, horizontal axis wind turbines (HAWTs). They have other inherent advantages; for example, they always face the wind. VAWTs include both a drag-type configuration, such as the Savonius rotor, and a lift-type configuration, such as the Darrieus rotor. The Savonius wind turbine is the simplest. Its operation depends on the difference in drag force when the wind strikes either the convex or concave part of its semi-cylindrical blades. It is good at self-starting and works independently of wind direction. However, its efficiency is relatively lower than that of the lift-type VAWTs. Due to its simple design and low construction cost, Savonius rotors are primarily used for water pumping and to generate wind power on a small scale and its large starting torque makes it suitable for starting other types of wind turbines that have inferior starting characteristics. Recently, some generators with high torque at low rotational speed, suitable for small-scale wind turbines, have been developed, suggesting that Savonius rotors may yet be used to generate electric power. The main goal of this research work is to improve the aerodynamic performance of the three bladed vertical axis Savonius wind turbine. Based on this goal, the objective of this project is to study the performance characteristics of the Savonius wind turbine scale models both experimentally and numerically. The turbine scale models will have different designs with different overlap ratios (ratio of gap between two adjacent blades and the rotor diameter) and without overlap within three blades. The experimental measurements and testing will be conducted in front of a low speed subsonic wind tunnel at different Reynolds number and the computational fluid dynamic (CFD) flow simulation around those design models will be performed by commercial CFD software FLUENT and GAMBIT.

H-type Darrieus vertical axis wind turbines (VAWT) have omnidirectional movement capability and can get more power compared to other VAWTs at high tip speed ratios (𝜆). However, its disadvantages are self-starting inability and low generated power at 𝜆 less than 1. The performance of H-type Darrieus wind turbine at 𝜆<1 was studied using double multiple stream tube (DMST) model and two-dimensional computational fluid dynamic (CFD) simulation. In CFD simulation, the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations were used and the turbulence model was solved with SST k-ω model. The performance of fifteen various wind turbines was determined at fourteen wind velocities by two solution methods. The effect of chord length, solidity, Reynolds number and Height to Diameter (H/D) ratio were investigated on generated torque, power and the time required to reach 𝜆=0.1. Increasing in the moment of inertia due to the increasing in required time to reach 𝜆=0.1. In the low TSRs, the wind turbines can generate higher torque and power in high Re numbers and solidities. The required time was reduced by an increase in Re number and solidity. Finally, the best ratio of H/D of H-type Darrieus wind turbines was defined to improve the turbine performance.

The vertical axis wind turbine (VAWT) with helical-blade has been developed, manufactured and applied in almost all developed countries. In Indonesia, vertical axis wind turbines are still not widely applied compared to horizontal axis wind turbines. Vertical axis wind turbines with helical-blade are still very rare in Indonesia. Research and development of the vertical axis wind turbine are needed because of its advantages compared to horizontal axis wind turbine. The advantages are: can operate in various wind directions, lower noise due to smaller tip speed ratio (TSR) and for large-scale, mechanical and electrical systems of turbine can be placed on ground. The aim of this research is to design a vertical axis wind turbine rotor with helical-blade that can be applied at low speeds and changing direction wind condition, such as urban wind characteristics. Performance analysis of wind turbine rotor is done by using double-multiple stream-tube (DMS) model approach. This research yields a rotor of vertical axis wind turbine with helical-blade with rotor length and diameter are 2m and 1m respectively, the rotor blade airfoil is DU-06-W-200 with chord length is 0.2m. From analysis, the optimum tip speed ratio of the rotor is 2.6 with a maximum power coefficient is 0.57.

A lift-driven vertical axis wind turbine (VAWT) generates peak power when it is rotating at high tip-speed ratios (TSR), at which time the blades encounter angles of attack (AOA) over a small range from zero to 30 degrees. However, its ability to self-start is dependent upon its performance at low TSRs, at which time the blades encounter a range of AOAs from zero to 180 degrees. A novel vented aerofoil is presented with the intention of improving the performance of a lift-driven VAWT at low TSRs without hampering the performance of the wind turbine at high TSRs. Computational fluid dynamics (CFD) simulation is used to predict the aerodynamic characteristics of a new vented aerofoil based on the well documented NACA0012 profile. Simulations are performed using the SST turbulence model. The results obtained show a reduction in the coefficient of tangential force (the force that generates torque on the wind turbine) at low AOAs (less than 90 degrees) of no more than 30%, while at high AOAs (more than 90 degrees) an improvement in the tangential force of over 100% is observed. Using a simple momentum based performance prediction model, these results suggest that this would lead to an increase in torque generation by a theoretical three-bladed VAWT of up to 20% at low TSRs and a minor reduction in coefficient of performance of up to 9% at TSR of 2 and closer to 1% at higher TSRs.