A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> Modern wind farms comprised of horizontal-axis wind turbines (HAWTs) require significant land resources to separate each wind turbine from the adjacent turbine wakes. This aerodynamic constraint limits the amount of power that can be extracted from a given wind farm footprint. The resulting inefficiency of HAWT farms is currently compensated by using taller wind turbines to access greater wind resources at high altitudes, but this solution comes at the expense of higher engineering costs and greater visual, acoustic, radar and environmental impacts. We investigated the use of counter-rotating vertical-axis wind turbines (VAWTs) in order to achieve higher power output per unit land area than existing wind farms consisting of HAWTs. Full-scale field tests of 10-m tall VAWTs in various counter-rotating configurations were conducted under natural wind conditions during summer 2010. Whereas modern wind farms consisting of HAWTs produce 2 to 3 watts of power per square meter of land area, these field tests indicate that power densities an order of magnitude greater can potentially be achieved by arranging VAWTs in layouts that enable them to extract energy from adjacent wakes and from above the wind farm. Moreover, this improved performance does not require higher individual wind turbine efficiency, only closer wind turbine spacing and a sufficient vertical flux of turbulence kinetic energy from the atmospheric surface layer. The results suggest an alternative approach to wind farming that has the potential to concurrently reduce the cost, size, and environmental impacts of wind farms. <s> BIB001 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> Abstract Small scale wind turbines installed within the built environment is classified as micro generation technology. This paper reports the investigation results of wind power application in buildings. First, general information is given for common type of wind turbines are used on buildings. Second, the wind aerodynamics and wind flows over the buildings are investigated based on local meteorological data and local building characteristics. However, to receive the highest potential wind energy resource and avoid turbulent areas, the tool of Computational Fluid Dynamics (CFD) has to be used to model the annual wind flows over buildings to help analyze, locate, and design wind turbines on and around buildings. Three different sample models for buildings and rural residential areas are explained with CFD models. <s> BIB002 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> Since millenaries humans have attempted to harness the wind energy through diverse means. Vertical axis wind turbines (VAWTs) were originally considered as very promising, before being superseded by the present, horizontal axis turbines. For various reasons, there is now a resurgence of interests for VAWTs, in particular Darrieus turbines. Using modern design tools and computational approaches, it should be possible to increase considerably the performance of traditional VAWTs, reaching a level almost comparable to that of horizontal axis turbines. Since VAWTs show many specific advantages (compact design, easier connection to gears/generator, easier blade control if needed, lower fatigue…), it is important to check quantitatively the efficiency of such turbines. This is the purpose of the present work, starting from the standard, straight Darrieus turbine (H-rotor). The aerodynamic investigation will be carried out for 20 different airfoils (Symmetric and Non-symmetric) by two-dimensional Computational Fluid Dynamics in order to maximize output torque coefficient and output power coefficient (efficiency). A considerable improvement of the H-rotor Darrieus turbine performance can be obtained in this manner. <s> BIB003 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> Abstract To minimize the visual impact, a micro-wind turbine was first designed to imitate lotus based on the Savonius type vertical axis wind rotor. It mainly consists of static blades (hereinafter referred to as “guide blades”) and rotor blades (hereinafter referred to as “semi-circular blades”). In the present paper, researches neglected the impact of the guide blades on the performance of the micro-wind turbine. The performance of the micro-wind rotor with semi-circular blades was compared to that of Savonius rotors with either semi-cylindrical or helically twisted blades by computational fluid dynamics. The performance for the each section of the semi-circular blades was discussed and analyzed. The results show that the performance of the wind rotor with semi-circular blades is comparable to that of the semi-cylindrical wind rotor, and is slightly lower than that of the helically twisted wind rotor. However, the semi-circular wind rotor runs more smoothly. <s> BIB004 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> Abstract This paper presents a preliminary energy and environmental analysis of a vertical-axis micro wind turbine with a nominal electric power of 3.7 kW. This prototype is called AM300. The main aim of the paper is to assess the amount of electric energy production of the AM300 and its feasible use in low wind speed areas. Furthermore, analyzing its low environmental impact, a potential installation in a natural protected area was considered. The turbine power curve was estimated by anemometric measurements. Furthermore, foreseeable prototype hybridization with PV array was analyzed. The environmental performance was assessed evaluating the soil, hydro geological, biodiversity and noise impacts. Finally, an analysis of the CO 2 emissions avoided is reported. The obtained results show good sustainability perspectives. <s> BIB005 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> Abstract Vertical axis wind turbines like the Darrieus turbine appear to be promising for the conditions of low wind speed, but suffer from a low efficiency compared to horizontal axis turbines. A fully detailed numerical analysis is introduced in this work to improve the global performance of this wind turbine. A comparison between ANSYS Workbench and Gambit meshing tools for the numerical modeling is performed to summarize a final numerical sequence for the Darrieus rotor performance. Then, this model sequence is applied for different blade airfoils to obtain the best performance. Unsteady simulations performed for different speed ratios and based on URANS turbulent calculations using sliding mesh approach. Results show that the accuracy of ANSYS Workbench meshing is improved by using SST K-omega model but it is not recommended for other turbulence models. Moreover, this CFD procedure is used in this paper to assess the turbine performance with different airfoil shapes (25 airfoils). The results introduced new shapes for this turbine with higher efficiency than the regular airfoils by 10%. In addition, blade pitch angle has been studied and the results indicated that the zero pitch angle gives best performance. <s> BIB006 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> Abstract A combined experimental and numerical investigation is carried out to study the performance of a micro vertical-axis wind turbine (VAWT) with variable-pitch. Three-dimensional numerical simulations are essentially employed, for the VAWT involves a low aspect ratio (AR) three straight blades with struts. The performance of the VAWT is experimentally measured using a wind tunnel, while large eddy simulation (LES) with dynamic smagorinsky subgrid scale (SGS) model is employed to help understand the associated flow structure. The effects of wind speed, turbulence intensity, airfoil shape, and strut mechanism with and without variable-pitch on the performance of the turbine are carefully assessed, both experimentally and numerically. The accuracy of the SGS model in predicting the laminar–turbulent transition is also examined. <s> BIB007 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> VAWT (Vertical axis wind turbines) pose several advantages over the horizontal axis machines that make them more suitable for applications where wind conditions are inherently turbulent. However, due to the complexity of VAWT aerodynamics, technical literature on the subject is very limited with research on VAWT performance mostly focused on steady wind analysis. This paper aims to numerically predict the performance of a 5 kW VAWT under fluctuating wind conditions through computational fluid dynamics modeling. Two dimensional VAWT models using symmetric and cambered blades were created with open field boundary extents. Fluctuating wind speed was imposed on the inlet with average magnitude of 5 m/s, amplitude of fluctuation of 10%, and frequency of fluctuation of 1 Hz. Results revealed that fluctuating wind imposes a detrimental effect on VAWT performance. A VAWT blade with 1.5% camber shows the best performance with the cycle-averaged unsteady power coefficient at 0.31 versus the optimum steady power coefficient of 0.34. In spite of increased available wind power due to the fluctuating wind at 233.13 Watts in one wind cycle compared to 229.69 Watts for the steady 5 m/s wind case, power generated by the camber bladed VAWT drops to 74.96 Watts from the steady wind rotor power of 78.32 Watts. <s> BIB008 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> Operating wind turbines generate tonal and broadband noises affecting the living environment adversely; especially small wind turbines located in the vicinity of human living places. Therefore, it is important to determine the level of noise pollution of such type of wind turbine installation. The current study carries out numerical prediction for aerodynamic noise radiated from an H-Darrieus Vertical Axis Wind Turbine. Incompressible LES (Large Eddy Simulation) is conducted to obtain the instantaneous turbulent flow field. The noise predictions are performed by the Ffowcs Williams and Hawkings (FW–H) acoustic analogy formulation. Simulations are performed for five different tip-speed ratios. First, the mean torque coefficient is compared with the experimental data, and good agreement is observed. Then, the research focuses on the broadband noises of the turbulent boundary layers and the tonal noises due to blade passing frequency. The contribution of the thickness, loading and quadrupole noises are investigated, separately. The results indicate a direct relation between the strength of the radiated noise and the rotational speed. Furthermore, the effect of receiver distance on the OASPL (Overall Sound Pressure Level) is investigated. It is concluded that the OASPL varies with a logarithmic trend with the receiver distance as it was expected. <s> BIB009 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> Abstract Noise disturbance is one of the major factors considered in the development of wind farms near urban areas, and therefore an accurate estimate of the noise levels generated by wind turbines is required before production and installation. Horizontal-axis wind turbines are the most popular type of turbines and the aeroacoustic noise generated by their rotating blades is known to be the most significant noise source. The region of the turbine blade that produces the strongest acoustic sources has been identified in published acoustic camera measurements. In the present work, a Large Eddy Simulation (LES) of this region is carried out using an annular computational domain, which leads to a significant reduction of computational expense compared to full blade simulations. The Ffowcs-Williams and Hawkings (FW–H) acoustic analogy is then used to predict the far field sound. Numerical results for a simulation of the CART-2 wind turbine show good agreement with the available experimental data. <s> BIB010 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> The effect of the spacing between adjacent building floors on the wind distribution and turbulence intensity was analysed using computational fluid dynamics in this study. Five computational models were created with floor spacing ranging from 0.8 m (benchmark) to 1.6 m. The three-dimensional Reynolds-Averaged Navier–Stokes equations along with the momentum and continuity equations were solved using the FLUENT code for obtaining the velocity and pressure field. Simulating a reference wind speed of 5.5 m/s, the findings from the study quantified that at a floor spacing of 1.6 m, the overall wind speed augmentation was 39 % which was much higher than the benchmark model (floor spacing = 0.8 m) indicating an amplification in wind speed of approximately 27 %. In addition, the results indicated a gradual reduction in turbulence kinetic energy by up to 53 % when the floor spacing was increased from 0.8 to 1.6 m. Although the concept was to integrate wind turbines into the building fabric, this study is limited to the assessment of the airflow inside the spaces of building floors which can be potentially harnessed by a vertical axis wind turbine. The findings of this work have indicated that there is a potential for integration which will lead on to future research in this area. <s> BIB011 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> Vertical axis wind turbines can be successfully installed in low wind speed conditions but its detailed starting characteristics in terms of starting torque, starting time and dynamic performances have not been investigated thoroughly which is important for increasing the energy yield of such turbines. Amongst their designs, H-Darrieus rotor, in spite of having good power coefficient, possesses poor self-starting features as symmetrical blade profiles are used most of the times. Instead of using symmetrical blades if unsymmetrical or cambered blades are used with high solidity, then starting performance of H-Darrieus rotor along with its power coefficients can be improved. Though this performance improvement measures are correlated with improvement in the starting characteristics, a detailed work in this direction would be useful and for this reason the present work has been carried out. Three types of blade designs have been considered; two unsymmetrical blades namely S815 and EN0005 and one conventional symmetrical NACA 0018 blade, and experiments are conducted using a centrifugal blower test rig for three-bladed H-Darrieus rotors using these three considered blades at low wind streams (4 m/s, 6 m/s and 8 m/s). Considering reality, the effects of flow non-uniformity and turbulence intensity on the rotor performance at optimum condition as well as flow physics have also been studied. It has been found that unsymmetrical S815 blade rotor has higher dynamic torque and higher power coefficient than unsymmetrical EN0005 and symmetrical NACA 0018 blade H-Darrieus rotors. <s> BIB012 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> This paper presents a straight-bladed VAWT (vertical axis wind turbine) model for the evaluation of aerodynamic forces and inertial contributions to rotor blade deformation. In this paper, a two-bladed VAWT is proposed and analyzed with CFD (computational fluid dynamics) and wind tunnel experiments in three-dimensional (3D) investigation. In wind tunnel experiments, pressure measurement system is presented to measure the pressure acting on a single blade of straight-bladed VAWT in the spanwise direction. In numerical analysis, 3D CFD models have been performed to simulate the aerodynamic forces characteristics of VAWT with k–e SST (Shear Stress Transport) (k–e) turbulence model. From comparing the results of the wind tunnel experiments and numerical analysis, it is found that the fluid force decreased with the increase of spanwise positions excluding the position of support structure. Furthermore, according to the result from six-component balance, the waveforms of the power coefficient Cpw have similar characteristics and show smaller values than CFD calculations. <s> BIB013 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> There is a demand of analyzing tilted Vertical Axis Wind Turbine (VAWT) for the emerging applications like VAWTs operating on high rise buildings, Floating Axis Wind Turbine (FAWT) functioning in deep sea, and so on. For this purpose numerical validation of an existing experimental work of Vertical Axis Wind Turbine (VAWT) in upright and tilted conditions has been carried out. The numerical validation is accomplished by means of Computational Fluid Dynamics (CFD) analysis by solving Unsteady Reynolds Averaged Navier–Stokes (URANS) equation. A rigorous parametric study of choosing a right turbulence model for solving URANS equation, mesh dependency analysis and optimum time step is comprehended. After choosing the right parameters, validation is performed. Following that the flow fields of upright and tilted conditions are visualized. The possible reasons of getting higher power coefficient in tilted condition have been discussed. While carrying out the study, it is observed that in case of tilted configuration the wake stream shifts downward. This feature of VAWT in tilted condition could lead into effective sea surface utilization in floating offshore wind farms. <s> BIB014 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> We present a comprehensive set of two-dimensional (2D) unsteady Reynolds-averaged Navier-Stokes (URANS) simulations of flow around a pair of counter-rotating vertical-axis wind turbines (VAWTs). The simulations are performed for two possible configurations of the counter-rotating VAWT pair, with various gaps between the two turbines, tip-speed-ratios and wind directions, in order to identify key flow mechanisms contributing to the enhanced performance of a pair of turbines compared to an isolated turbine. One of the key mechanisms identified, for the case of two turbines arrayed side-by-side with respect to the incoming wind, is the change of lateral velocity in the upwind path of each turbine due to the presence of the neighbouring turbine, making the direction of local flow approaching the turbine blade more favourable to generate lift and torque. The results also show that the total power of a staggered pair of turbines cannot surpass that of a side-by-side pair of turbines. Some implications of the present results for the prediction of the performance of single and multiple rows (or a farm) of VAWTs are also discussed. The local flow mechanisms identified in the present study are expected to be of great importance when the size of the farm is relatively small. <s> BIB015 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> Abstract Unlike horizontal axis wind turbines (HAWTs), the Darrieus vertical axis wind turbine (H-type VAWT) has been the subject of only a few recent studies directed at improving its self-starting capability and/or aerodynamic performance. The technique currently used for improving the performance of this type of turbine is pitch angle control. This paper presents intelligent blade pitch control for enhancing the performance of H-type VAWTs with respect to power output. To determine the optimum pitch angles, ANSYS Fluent Computational Fluid Dynamics (CFD) software was used for a study of the aerodynamic performance of a 2D variable pitch angle H-type VAWT at a variety of tip speed ratios (TSRs). For each case examined, the power coefficient ( C p ) was calculated and compared to published experimental and CFD findings. The results obtained from the CFD model were then applied for the construction of an aerodynamic model of an H-type VAWT rotor, which constituted a prerequisite for designing an intelligent pitch angle controller using a multilayer perceptron artificial neural network (MLP-ANN) method. The performance of the MLP-ANN blade pitch controller was compared to that of a conventional controller (PID). The findings demonstrate that for an H-type VAWT, compared to a conventional PID controller, an MLP-ANN results in superior power output. <s> BIB016 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> Abstract: The suitability of using an upstream deflector to improve the efficiency of a vertical axis wind turbine is presented in this study. A two-dimensional vertical axis wind turbine (VAWT) was modelled and simulated using ANSYS Fluent 14.0 computational fluid dynamics (CFD) software to solve the k-epsilon (RNG) turbulence model. Firstly, the open rotor design was optimised by varying orientation and pitch angle, prior to analysing the effect increasing wind speed had on the turbine performance. A maximum efficiency of 19.101% was achieved and was used as the open rotor design. A series of curved upstream deflectors were then evaluated in terms of efficiency improvements against the original open rotor design. Installation of the deflector resulted in a redirection of the fluid flow from the returning turbine blade, therefore reducing the negative torque induced on the system. Additionally, deflector width angles of 45 o and 36 o were found to improve the turbine performance by 1.266%. Finally, a scale model of the wind turbine was constructed and experimentally tested using a wind tunnel. No correlation between the CFD and experimental results was found due to variations in the wind speed tested by both methods. However, the VAWT design operated at a reasonably efficient level during the experimental testing, even under suboptimal conditions. <s> BIB017 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> The increasing price of fossil derivatives, global warming and energy market instabilities, have led to an increasing interest in renewable energy sources such as wind energy. Amongst the different typologies of wind generators, small scale Vertical Axis Wind Turbines (VAWT) present the greatest potential for off grid power generation at low wind speeds. In the present work, Computational Fluid Dynamic (CFD) simulations were performed in order to investigate the performance of an innovative configuration of straight-blades Darrieus-style vertical axis micro wind turbine, specifically developed for small scale energy conversion at low wind speeds. The micro turbine under investigation is composed of three pairs of airfoils, consisting of a main and auxiliary blades with different chord lengths. The simulations were made using the open source finite volume based CFD toolbox OpenFOAM, considering different turbulence models and adopting a moving mesh approach for the turbine rotor. The simulated data were reported in terms of dimensionless power coefficients for dynamic performance analysis. The results from the simulations were compared to the data obtained from experiments on a scaled model of the same VAWT configuration, conducted in a closed circuit open chamber wind tunnel facility available at the Laboratory of Industrial Measurements (LaMI) of the University of Cassino and Lazio Meridionale (UNICLAM). From the proposed analysis, it was observed that the most suitable model for the simulation of the performances of the micro turbine under investigation is the one-equation Spalart-Allmaras, even if under the conditions analysed in the present work and for TSR values higher than 1.1, some discrepancies between numerical and experimental data can be observed. <s> BIB018 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> A Double Multiple Streamtube model, a free-wake vortex model (both widely used for vertical axis wind turbine design) and RANS CFD simulations are used in this work to predict the performance of the 17 m Vertical Axis Wind Turbine, field tested by Sandia National Laboratories. The three-dimensional, full scale calculations are compared with the experiments in terms of power coefficient, power and instantaneous turbine torque to assess the validity of each model. Additionally, the two aerodynamic models and RANS CFD are compared to each other in terms of thrust and lateral force. The two models and CFD agree well with the experiments at the turbine optimal tip speed ratio. However, away from the optimal tip speed ratio, the streamtube model significantly deviates from the experimental data and from the other numerical models. RANS CFD gives a good agreement with the experiments, slightly underestimating the power coefficient at every tip speed ratio tested. The vortex model proves to be a useful tool with a better accuracy than the streamtube model and a much lower computational cost compared to RANS CFD. <s> BIB019 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> Accurate prediction of the performance of a vertical-axis wind turbine (VAWT) using Computational Fluid Dynamics (CFD) simulation requires a domain size that is large enough to minimize the effects of blockage and uncertainties in the boundary conditions on the results. It also requires the employment of a sufficiently fine azimuthal increment (dθ) combined with a grid size at which essential flow characteristics can be accurately resolved. The current study systematically investigates the effect of the domain size and azimuthal increment on the performance of a 2-bladed VAWT operating at a moderate tip speed ratio of 4.5 using 2-dimensional and 2.5-dimensional simulations with the unsteady Reynolds-averaged Navier-Stokes (URANS). The grid dependence of the results is studied using three systematically refined grids. The turbine has a low solidity of 0.12 and a swept area of 1 m2. Refining dθ from 10.0° to 0.5° results in a significant (≈43%) increase in the predicted power coefficient (CP) while the effect is negligible (≈0.25%) with further refinement from 0.5° to 0.05° at the given λ. Furthermore, a distance from the turbine center to the domain inlet and outlet of 10D (D: diameter of turbine) each, a domain width of 20D 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. <s> BIB020 </s> A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment <s> Micro-Small Scale <s> Wind velocity distribution and the vortex around the wind turbine present a significant challenge in the development of straight-bladed vertical axis wind turbines (VAWTs). This paper is intended to investigate influence of tip vortex on wind turbine wake by Computational Fluid Dynamics (CFD) simulations. In this study, the number of blades is two and the airfoil is a NACA0021 with chord length of c = 0.265 m. To capture the tip vortex characteristics, the velocity fields are investigated by the Q-criterion iso-surface (Q = 100) with shear-stress transport (SST) k-ω turbulence model at different tip speed ratios (TSRs). Then, mean velocity, velocity deficit and torque coefficient acting on the blade in the different spanwise positions are compared. The wind velocities obtained by CFD simulations are also compared with the experimental data from wind tunnel experiments. As a result, we can state that the wind velocity curves calculated by CFD simulations are consistent with Laser Doppler Velocity (LDV) measurements. The distribution of the vortex structure along the spanwise direction is more complex at a lower TSR and the tip vortex has a longer dissipation distance at a high TSR. In addition, the mean wind velocity shows a large value near the blade tip and a small value near the blade due to the vortex effect. <s> BIB021
Decentralised or on-site energy generation by exploiting various types of energy resources has the prospective to deliver extensively applicable low carbon electricity generation at the urban or built environment level  BIB011 . Generation of power at the point of use can minimise the energy loss associated with the transmission of electricity. Due to these, micro to small-scale renewables such as solar panels and wind turbines have gained increasing attention. Small micro-wind turbines are generally classified based on swept area (<25 m 2 ) and have rated power of up to 6 kW BIB002 25] . Different types of small micro wind turbine are shown in Figure 2 . This section will review the recent studies that assess the wind energy systems in the micro-small scale using CFD and addresses the challenges associated with its applications, including design, optimisation, low velocity and high turbulence of urban wind, vibration and noise problems. De-Santoli et al. BIB005 conducted CFD and experimental analysis of an AM300 vertical axis microwind turbine with an electrical power of 3.7 kW. The study assessed the viability and energy generation in low wind speed locations. The initial energy results demonstrated that the electricity production of the prototype was higher than that generated by a typical generator with the same technical features. Hence, a lower cut in wind speed for the power curve was achieved. The CFD analysis highlighted that adding the convergent duct to the H-rotor Darrieus turbine (see Figure 3 ) improved its energy generation. The percentage of power rises at roughly 125% for wind speed equal to 8 m/s. Although the CFD model was able to evaluate the speed amplification effect due to the convergent duct, experiments were conducted to assess the power increase. De-Santoli et al. BIB005 conducted CFD and experimental analysis of an AM300 vertical axis micro-wind turbine with an electrical power of 3.7 kW. The study assessed the viability and energy generation in low wind speed locations. The initial energy results demonstrated that the electricity production of the prototype was higher than that generated by a typical generator with the same technical features. Hence, a lower cut in wind speed for the power curve was achieved. The CFD analysis highlighted that adding the convergent duct to the H-rotor Darrieus turbine (see Figure 3 ) improved its energy generation. The percentage of power rises at roughly 125% for wind speed equal to 8 m/s. Although the CFD model was able to evaluate the speed amplification effect due to the convergent duct, experiments were conducted to assess the power increase. A similar study by El-Zahaby et al.  used a 2-D axisymmetric CFD model based on standard k-ε turbulence model to investigate a micro wind turbine contained in a diffuser with flanges to enhance power generation. The work focused on the influence of flange's angles on velocity at diffuser entrance. The verification of the present model showed good agreement among earlier published experimental data. The numerical results demonstrated the vortices which were generated at the leeward side of the flange which caused a drop in pressure and increased the diffuser's flow rate. The work concluded that the right flange with 15° angle was the most effective in terms of accelerating the flow at the inlet of diffuser. The work only focused on the diffuser geometry and did not consider the rotor of the turbine. Several recent studies have focused on optimizing the blades of micro scale wind turbines using CFD modelling. A 3D CFD analysis of the performance of a lotus shape wind turbine based on the Savonius type VAWT was studied by Wang and Zhan BIB004 . Using CFD based on unsteady continuity RANS with realisable k-ε turbulence model, three types of configurations were compared as shown in Figure 4 ; wind turbine with semi-circular blades, Savonius type with helically-twisted blades or semi-cylindrical. Its rotation was simulated using the sliding mesh method in CFD. The results showed that the performance of the semi-circular blade configuration was equivalent to that of the semi-cylindrical configuration and was lower as compared to the helically-twisted type. The study, however, ignored the influence of the guide blades on the systems performance. Mohamed et al. BIB006 used CFD based on the SST k-ω and Realisable k-ε models in order to investigate 25 different types of blade aerofoil sections and blade pitch angles (−10-10°) of a small Hrotor Darrieus turbine. The results showed that LS (1)-0413 aerofoil had a power coefficient 10% higher than the NACA 0018. In another study BIB003 , the same author compared the performance of 20 different symmetrical and unsymmetrical aerofoil shapes ( Figure 5 ) to maximise the power and A similar study by El-Zahaby et al.  used a 2-D axisymmetric CFD model based on standard k-ε turbulence model to investigate a micro wind turbine contained in a diffuser with flanges to enhance power generation. The work focused on the influence of flange's angles on velocity at diffuser entrance. The verification of the present model showed good agreement among earlier published experimental data. The numerical results demonstrated the vortices which were generated at the leeward side of the flange which caused a drop in pressure and increased the diffuser's flow rate. The work concluded that the right flange with 15 • angle was the most effective in terms of accelerating the flow at the inlet of diffuser. The work only focused on the diffuser geometry and did not consider the rotor of the turbine. Several recent studies have focused on optimizing the blades of micro scale wind turbines using CFD modelling. A 3D CFD analysis of the performance of a lotus shape wind turbine based on the Savonius type VAWT was studied by Wang and Zhan BIB004 . Using CFD based on unsteady continuity RANS with realisable k-ε turbulence model, three types of configurations were compared as shown in Figure 4 ; wind turbine with semi-circular blades, Savonius type with helically-twisted blades or semi-cylindrical. Its rotation was simulated using the sliding mesh method in CFD. The results showed that the performance of the semi-circular blade configuration was equivalent to that of the semi-cylindrical configuration and was lower as compared to the helically-twisted type. The study, however, ignored the influence of the guide blades on the systems performance. A similar study by El-Zahaby et al.  used a 2-D axisymmetric CFD model based on standard k-ε turbulence model to investigate a micro wind turbine contained in a diffuser with flanges to enhance power generation. The work focused on the influence of flange's angles on velocity at diffuser entrance. The verification of the present model showed good agreement among earlier published experimental data. The numerical results demonstrated the vortices which were generated at the leeward side of the flange which caused a drop in pressure and increased the diffuser's flow rate. The work concluded that the right flange with 15° angle was the most effective in terms of accelerating the flow at the inlet of diffuser. The work only focused on the diffuser geometry and did not consider the rotor of the turbine. Several recent studies have focused on optimizing the blades of micro scale wind turbines using CFD modelling. A 3D CFD analysis of the performance of a lotus shape wind turbine based on the Savonius type VAWT was studied by Wang and Zhan BIB004 . Using CFD based on unsteady continuity RANS with realisable k-ε turbulence model, three types of configurations were compared as shown in Figure 4 ; wind turbine with semi-circular blades, Savonius type with helically-twisted blades or semi-cylindrical. Its rotation was simulated using the sliding mesh method in CFD. The results showed that the performance of the semi-circular blade configuration was equivalent to that of the semi-cylindrical configuration and was lower as compared to the helically-twisted type. The study, however, ignored the influence of the guide blades on the systems performance. Mohamed et al. BIB006 used CFD based on the SST k-ω and Realisable k-ε models in order to investigate 25 different types of blade aerofoil sections and blade pitch angles (−10-10°) of a small Hrotor Darrieus turbine. The results showed that LS (1)-0413 aerofoil had a power coefficient 10% higher than the NACA 0018. In another study BIB003 , the same author compared the performance of 20 different symmetrical and unsymmetrical aerofoil shapes ( Figure 5 ) to maximise the power and Mohamed et al. BIB006 used CFD based on the SST k-ω and Realisable k-ε models in order to investigate 25 different types of blade aerofoil sections and blade pitch angles (−10-10 • ) of a small Computation 2018, 6, 24 6 of 37 H-rotor Darrieus turbine. The results showed that LS (1)-0413 aerofoil had a power coefficient 10% higher than the NACA 0018. In another study BIB003 , the same author compared the performance of 20 different symmetrical and unsymmetrical aerofoil shapes ( Figure 5 ) to maximise the power and torque coefficient. The results indicated that the S-1046 aerofoil section led to a 27% increase in maximum power output coefficient compared to the standard symmetrical NACA aerofoils. Elkhoury et al. BIB007 used CFD based on LES or large eddy simulation with the dynamic SGS or Smagorinsky-Subgrid scale model to investigate the micro VAWT's performance with variable-pitch. The variable-pitch mechanism was simulated using the sliding mesh method. The results showed that thicker aerofoils had improved performance for the studied high-solidity ratio fixed pitch wind turbine. Furthermore, good consistency was seen among the LES numerical model and experimental results, both for the variable and fixed pitch mechanisms as detailed in Figure 6 . torque coefficient. The results indicated that the S-1046 aerofoil section led to a 27% increase in maximum power output coefficient compared to the standard symmetrical NACA aerofoils. Elkhoury et al. BIB007 used CFD based on LES or large eddy simulation with the dynamic SGS or Smagorinsky-Subgrid scale model to investigate the micro VAWT's performance with variable-pitch. The variable-pitch mechanism was simulated using the sliding mesh method. The results showed that thicker aerofoils had improved performance for the studied high-solidity ratio fixed pitch wind turbine. Furthermore, good consistency was seen among the LES numerical model and experimental results, both for the variable and fixed pitch mechanisms as detailed in Figure 6 . VAWTs such as H-Darrieus rotor can be effective in low wind speed conditions but since blades with symmetrical profiles are generally used, it had poor self-starting capabilities. Its starting performance can be improved by using high solidity cambered or unsymmetrical blades. Bausas and Danao BIB008 used CFD modelling to study the overall performance of a camber-bladed VAWT under VAWTs such as H-Darrieus rotor can be effective in low wind speed conditions but since blades with symmetrical profiles are generally used, it had poor self-starting capabilities. Its starting performance can be improved by using high solidity cambered or unsymmetrical blades. Bausas and Danao BIB008 used CFD modelling to study the overall performance of a camber-bladed VAWT under varying wind conditions. The CFD analysis highlighted that variable wind causes a negative effect on the VAWT's performance with up to 9% drop in pressure coefficient. In addition, the camber slightly improved VAWT's performance. Similarly, Sengupta et al. BIB012 also conducted a CFD investigation to evaluate the self-starting features and efficiency of a H-Darrieus turbine with unsymmetrical blades under low wind conditions. The study concluded that the unsymmetrical blades had a higher power and static and dynamic torque coefficient than the evaluated symmetrical blades. Li et al. BIB013 conducted 3D transient CFD analysis of a straight-bladed turbine to assess the influence of near-wake and thrust coefficient. The results showed that the momentum amount is minimum at the tip of blade and maximum at the centre of the blade. Furthermore, the CFD model based on the k-epsilon SST transport model provided reasonable predictions as compared to the experimental results. In another study, Li et al.  predicted the aerodynamic performance of the same VAWT model in the span-wise direction. Based on the evaluation of the experimental and CFD data, it was seen that the fluid force reduced as the spanwise position increased. The study of Abdalrahman et al. BIB016 focused on investigating an intelligent controller for blade pitch of a small H-type VAWT for optimising its power production. CFD was used to examine the performance at various tip speed ratios. The flow was investigated using two methods: sliding mesh and MRF or multiple reference frame method. The power coefficient was solved for each configuration and validated with available experimental data. Due to the complexity related to the dynamic response modelling of the turbine rotor, the numerical data was used for mapping the rotor's variable-and fixed-pitch angle system models using an artificial neural network. Results showed that the proposed technique improved the output by up to 25%, as compared to a fixed blade configuration. One of the benefits of the VAWT is its capability to extract wind power from any wind angle or direction and hence it does not require costly pitch and yaw system  . Although this also results in deceleration because of the torque (negative) on the returning blades, which then decreases performance. To address this, Stout et al. BIB017 examined the efficiency improvement of a small VAWT as a result of the addition of an upstream deflector or guide vanes. A 2D VAWT was simulated using ANSYS Fluent CFD to calculate the unsteady Navier-Stokes equation and the k-epsilon RNG model. At the initial process, the performance was enhanced by modifying the pitch angle and orientation, before assessing the impact on increasing wind velocity had on the turbine efficiency. Results showed that it reached 19% maximum efficiency and employed as the design for open rotor. Installed deflectors redirected the fluid flow from the returning turbine blade, thus minimising the negative torque on the device. Moreover, deflectors with width angles between 36 and 45 • were observed to enhance the performance of the turbine by up to 1.27%. CFD simulations were conducted by Arpino et al. BIB018 to examine the optimal formation of straight-blade Darrieus type VAWT, particularly designed for energy conversion at low wind velocities. The system consisted of three aerofoilpairs, composed of primary and secondary blades with various chord lengths. Analyses were conducted using CFD OpenFOAM, taking into account various turbulence models and using the moving mesh method. The simulation data were compared to the results gathered from the experimental wind tunnel tests of a scaled model and it was concluded that the most accurate model for the analysis of the investigated turbine was the Spalart-Allmaras one equation model. Various numerical models were developed over the years to accurately simulate the aerodynamic performance of VAWTs. The numerical models can be categorised into the main types, stream-tube, vortex method and CFD modelling. The study of Delafin et al. BIB019 compared the RANS CFD modelling method with other two low order aerodynamic models (double multiple streamtube model and free-wake vortex mode) based on the prediction of VAWT's performance, examined by Sandia National Laboratories. The models were assessed based on the prediction of the power coefficient, power, thrust, lateral force and instantaneous turbine torque. All the models agreed well with the test at the optimum tip speed ratio (see Figure 7 ), but away from the optimal value, the stream tube model greatly differs from other numerical models and experimental data. The RANS CFD model results compared well with the conducted tests, but to some extent underestimating the power coefficient values. CFD model results compared well with the conducted tests, but to some extent underestimating the power coefficient values. Figure 7 . Error of the predicted power by CFD, stream-tube, vortex methods from the experiments at several tip speed ratios (TSR) BIB019 . Accurate prediction of the performance of turbines by means of CFD necessitates an adequately fine grid or mesh resolution and azimuthal increment in order to capture important flow details. The size of the computational domains also requires to be adequately large to minimise the impact of blockage caused by the device in the domain. The work of Rezaeiha et al. BIB020 examined the effect of the aforementioned computational parameters on a small two-bladed VAWT operating at 4.5 tip speed ratio using CFD with the uRANS or unsteady Reynolds averaged Navier-Strokes. Figure 8 shows the sizing of the computational domain. The study highlighted that a distance from the turbine center to the domain inlet di and outlet do of 10 D (10 × diameter of turbine) each, a 20D domain width W and a diameter of the rotating core dc of 1.5D were seen to be safe choices to reduce the effects of blockage and uncertainty in the boundary conditions on the results. Klein et al.  used CFD modelling to investigate the impact of blockage on the blade performance. The study compared the results of the CFD code with a LLFVW or Lifting Line Free Vortex Wake code and wind tunnel experiment. Good comparison was observed between the numerical and wind tunnel data. In the study of Chowdhury et al. BIB014 , a parametric investigation of turbulence models, time step, and mesh independence were conducted for accurate simulation of an upright and tilted small VAWT. Based on the results, the Spalart-Allmaras turbulence model had the worst performance in regards to vortices capturing. While the SST k-omega modelled the vortices in wake better compared to Spalart-Allmaras and RNG k-epsilon turbulence models. The analysis proved that CFD was better as compared to BEM in terms of aerodynamic feature predictions. Furthermore, the tilted VAWT configuration produced better downwind torque than the upright VAWT configuration. Yang et al. BIB021 examined the effect of tip vortex on small VAWT wake using CFD simulations based on the k omega SST or shear-stress transport model at various TSRs. To accurately study the tip vortex formation, the grid which had a substantial effect on the vortex evolution was concentrated in the rotor blade area, as shown in Figure 9 . The vortex structure distribution was more complex with the span wise direction at a lower TSR and the tip vortex had an extended dissipation distance at a high TSR. Moreover, the average wind velocity results demonstrated a small value beside the blade and large value behind the blade tip, due to the vortex effect. Accurate prediction of the performance of turbines by means of CFD necessitates an adequately fine grid or mesh resolution and azimuthal increment in order to capture important flow details. The size of the computational domains also requires to be adequately large to minimise the impact of blockage caused by the device in the domain. The work of Rezaeiha et al. BIB020 examined the effect of the aforementioned computational parameters on a small two-bladed VAWT operating at 4.5 tip speed ratio using CFD with the uRANS or unsteady Reynolds averaged Navier-Strokes. Figure 8 shows the sizing of the computational domain. The study highlighted that a distance from the turbine center to the domain inlet di and outlet do of 10 D (10 × diameter of turbine) each, a 20D domain width W and a diameter of the rotating core dc of 1.5D were seen to be safe choices to reduce the effects of blockage and uncertainty in the boundary conditions on the results. Klein et al.  used CFD modelling to investigate the impact of blockage on the blade performance. The study compared the results of the CFD code with a LLFVW or Lifting Line Free Vortex Wake code and wind tunnel experiment. Good comparison was observed between the numerical and wind tunnel data. In the study of Chowdhury et al. BIB014 , a parametric investigation of turbulence models, time step, and mesh independence were conducted for accurate simulation of an upright and tilted small VAWT. Based on the results, the Spalart-Allmaras turbulence model had the worst performance in regards to vortices capturing. While the SST k-omega modelled the vortices in wake better compared to Spalart-Allmaras and RNG k-epsilon turbulence models. The analysis proved that CFD was better as compared to BEM in terms of aerodynamic feature predictions. Furthermore, the tilted VAWT configuration produced better downwind torque than the upright VAWT configuration. Yang et al. BIB021 examined the effect of tip vortex on small VAWT wake using CFD simulations based on the k omega SST or shear-stress transport model at various TSRs. To accurately study the tip vortex formation, the grid which had a substantial effect on the vortex evolution was concentrated in the rotor blade area, as shown in Figure 9 . The vortex structure distribution was more complex with the span wise direction at a lower TSR and the tip vortex had an extended dissipation distance at a high TSR. Moreover, the average wind velocity results demonstrated a small value beside the blade and large value behind the blade tip, due to the vortex effect. Small VAWTs can be easily integrated into urban areas for decentralised power generation. Due to its size, it is generally considered to be sufficiently quiet assuming that its utilisation in urban environments means that the noise output will hardly exceed that of the surroundings, hence only a small number of work has studied its noise output. However, it is still important to conduct noise prediction during the early stage turbine design so that its integration into urban environments can be approved. Botha et al.  developed on optimised technique for calculating aerodynamically produced noise by a small VAWT. This technique enhances the current prediction of noise and integrates currently established aerofoil prediction models. The self-noise methods and inflow turbulence were considered. Time-dependent CFD simulations were conducted to calculate or the aerodynamic solution and noise predictions were reliant on the input data. The analytical flow approaches were also compared against the CFD results to quantity errors in the previous method. The results showed that the dominant source of noise was the inflow turbulence. The work concluded that the integration with CFD enhanced the prediction accuracy when compared with analytic methods. While Ghasemian and Nejat BIB009 and Wasala et al. BIB010 also employed CFD but using LES to predict the flow field in combination with FW-H or Ffowcs Williams and Hawkings method to predict the generated noise by a wind turbine at different tip speed ratios. Several recent studies (Bremseth and Duraisamy  , Dabiri BIB001 , Giorgetti et al.  ) suggested that unlike HAWTs, VAWTs demand less stringent spacing requirements and optimising the positioning and rotation (co-/counter-rotating) of the closely spaced multi VAWT arrangement, could lead to improved performance. Giorgetti et al.  used CFD to investigate the enhancement in power that can be achieved by setting medium to high solidity and thus low TSR Darrieus micro turbines in close proximity. CFD simulations were conducted to assess the aerodynamic interferences in twoand four-rotor formations as shown in Figure 10 . In addition, the performance of counter-rotating and co-rotating arrangements was compared. The results of the simulations demonstrated a rise in production of around 10% as compared to an isolated turbine. The study concluded that acceleration Small VAWTs can be easily integrated into urban areas for decentralised power generation. Due to its size, it is generally considered to be sufficiently quiet assuming that its utilisation in urban environments means that the noise output will hardly exceed that of the surroundings, hence only a small number of work has studied its noise output. However, it is still important to conduct noise prediction during the early stage turbine design so that its integration into urban environments can be approved. Botha et al.  developed on optimised technique for calculating aerodynamically produced noise by a small VAWT. This technique enhances the current prediction of noise and integrates currently established aerofoil prediction models. The self-noise methods and inflow turbulence were considered. Time-dependent CFD simulations were conducted to calculate or the aerodynamic solution and noise predictions were reliant on the input data. The analytical flow approaches were also compared against the CFD results to quantity errors in the previous method. The results showed that the dominant source of noise was the inflow turbulence. The work concluded that the integration with CFD enhanced the prediction accuracy when compared with analytic methods. While Ghasemian and Nejat BIB009 and Wasala et al. BIB010 also employed CFD but using LES to predict the flow field in combination with FW-H or Ffowcs Williams and Hawkings method to predict the generated noise by a wind turbine at different tip speed ratios. Several recent studies (Bremseth and Duraisamy  , Dabiri BIB001 , Giorgetti et al.  ) suggested that unlike HAWTs, VAWTs demand less stringent spacing requirements and optimising the positioning and rotation (co-/counter-rotating) of the closely spaced multi VAWT arrangement, could lead to improved performance. Giorgetti et al.  used CFD to investigate the enhancement in power that can be achieved by setting medium to high solidity and thus low TSR Darrieus micro turbines in close proximity. CFD simulations were conducted to assess the aerodynamic interferences in twoand four-rotor formations as shown in Figure 10 . In addition, the performance of counter-rotating and co-rotating arrangements was compared. The results of the simulations demonstrated a rise in production of around 10% as compared to an isolated turbine. The study concluded that acceleration Small VAWTs can be easily integrated into urban areas for decentralised power generation. Due to its size, it is generally considered to be sufficiently quiet assuming that its utilisation in urban environments means that the noise output will hardly exceed that of the surroundings, hence only a small number of work has studied its noise output. However, it is still important to conduct noise prediction during the early stage turbine design so that its integration into urban environments can be approved. Botha et al.  developed on optimised technique for calculating aerodynamically produced noise by a small VAWT. This technique enhances the current prediction of noise and integrates currently established aerofoil prediction models. The self-noise methods and inflow turbulence were considered. Time-dependent CFD simulations were conducted to calculate or the aerodynamic solution and noise predictions were reliant on the input data. The analytical flow approaches were also compared against the CFD results to quantity errors in the previous method. The results showed that the dominant source of noise was the inflow turbulence. The work concluded that the integration with CFD enhanced the prediction accuracy when compared with analytic methods. While Ghasemian and Nejat BIB009 and Wasala et al. BIB010 also employed CFD but using LES to predict the flow field in combination with FW-H or Ffowcs Williams and Hawkings method to predict the generated noise by a wind turbine at different tip speed ratios. Several recent studies (Bremseth and Duraisamy  , Dabiri BIB001 , Giorgetti et al.  ) suggested that unlike HAWTs, VAWTs demand less stringent spacing requirements and optimising the positioning and rotation (co-/counter-rotating) of the closely spaced multi VAWT arrangement, could lead to improved performance. Giorgetti et al.  used CFD to investigate the enhancement in power that can be achieved by setting medium to high solidity and thus low TSR Darrieus micro turbines in close proximity. CFD simulations were conducted to assess the aerodynamic interferences in two-and four-rotor formations as shown in Figure 10 . In addition, the performance of counter-rotating and co-rotating arrangements was compared. The results of the simulations demonstrated a rise in production of around 10% as compared to an isolated turbine. The study concluded that acceleration of the freestream flow among the turbines was the reason of the improvement of power extraction through re-energisation and contraction of the turbine wakes. A similar CFD study was conducted by Zanforlin and Nishino BIB015 to investigate the enhancement of power generation due to the pairing of counter-rotating VAWTs. They concluded that two main mechanisms contribute to the power increase of a side by side counter-rotating VAWTs: (1) modification of lateral velocity in the windward pathway due to the existence of the adjacent wind turbine and (2) wake contraction in the downwind path. Ghasemian et al.  emphasised that the grouping of VAWTs results in distributed flows downwind of rotors with reduced wind speed and the optimum arrangement can enhance the power generation. Table 1 summarises the different CFD studies on wind turbines in the micro to small scale including augmentation using guide vanes and shrouds, blade profile modification optimisation, wind turbine wake interaction, aeroacoustics of wind turbines, unsteady wind flow conditions and self-starting characteristics. The effects of different geometrical and operating parameters including tip speed ratio, blade number and blade shapes, wind speed, solidity on the wind turbine performance and self-starting characteristics were investigated. Several studies highlighted the importance of CFD in accelerating the design process of micro to small scale wind turbines and bringing down the overall cost of design. Many research on micro to small scale wind turbines have used CFD for designing the blades and computing the forces acting on it. Various numerical models were established over the years to accurately simulate the aerodynamic performance of micro to small scale wind turbines. The numerical models can be mainly categorised into stream-tube, vortex method and CFD modelling. Many of the CFD studies carried out used low order models including the k-epsilon, SST k-ω, or Spalart-Allmaras models and few investigations used models such as LES and Reynolds Stress Transport models. Few studies have studied the noise output of small scale wind turbines. Several studies have employed CFD to predict the turbulent flow field in combination with analytical method to accurately predict the noise generation by a wind turbine. A similar CFD study was conducted by Zanforlin and Nishino BIB015 to investigate the enhancement of power generation due to the pairing of counter-rotating VAWTs. They concluded that two main mechanisms contribute to the power increase of a side by side counter-rotating VAWTs: (1) modification of lateral velocity in the windward pathway due to the existence of the adjacent wind turbine and (2) wake contraction in the downwind path. Ghasemian et al.  emphasised that the grouping of VAWTs results in distributed flows downwind of rotors with reduced wind speed and the optimum arrangement can enhance the power generation. Table 1 summarises the different CFD studies on wind turbines in the micro to small scale including augmentation using guide vanes and shrouds, blade profile modification optimisation, wind turbine wake interaction, aeroacoustics of wind turbines, unsteady wind flow conditions and self-starting characteristics. The effects of different geometrical and operating parameters including tip speed ratio, blade number and blade shapes, wind speed, solidity on the wind turbine performance and self-starting characteristics were investigated. Several studies highlighted the importance of CFD in accelerating the design process of micro to small scale wind turbines and bringing down the overall cost of design. Many research on micro to small scale wind turbines have used CFD for designing the blades and computing the forces acting on it. Various numerical models were established over the years to accurately simulate the aerodynamic performance of micro to small scale wind turbines. The numerical models can be mainly categorised into stream-tube, vortex method and CFD modelling. Many of the CFD studies carried out used low order models including the k-epsilon, SST k-ω, or Spalart-Allmaras models and few investigations used models such as LES and Reynolds Stress Transport models. Few studies have studied the noise output of small scale wind turbines. Several studies have employed CFD to predict the turbulent flow field in combination with analytical method to accurately predict the noise generation by a wind turbine. The proposed WT's electricity production is 6000 kWh annually. The electricity generation is improved by 50% with the use of PV array to the device. Wang and Zhan (2013) Savonius VAWT 2 -FLUENT, RANS, 3D, Realizable k-ε The wind rotor performance integrated with semi-circular blades was almost similar to the semi-cylindrical wind rotor and slower compared to the shape of spiral twisted wind rotor but the semi-circular wind rotor operates more smoothly.