Experimental Study for Three and Six Buckets of Sim-Savonius

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 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%.

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

This report presents the study of fluid-structure interaction (FSI) of a 5kW horizontal axis wind turbines (HAWT). The motivation of the current investigation is to address the FSI problem of HAWT in the whole flow field analysis with hybrid turbulence model method which is used to find out the flow and structure characteristics of wind turbine in operation under different tip speed ratio (TSR). The target of current work is to obtain detailed information of flow field and structure response simultaneously using the finite element analysis (FEA) method as well as providing new reliable and accurate approach which could be quickly and economically employed in wind turbine FSI problem analysis. In this report, a detailed and comprehensive literature review related to FSI problem of wind turbine has been presented and includes aerodynamic, wind turbine theory, computational fluid dynamic, fluid structure interaction and aeroelastic stability. A 5kW wind turbine is designed according to blade element momentum (BEM) method and a 3D wind turbine modeling is generated in SolidWorks. The 3D wind turbine modeling is imported into FEA software by coupling with the structure domain and the fluid domain to achieve FSI analysis and different TSR are applied to the computational fluid dynamics (CFD) analysis to gain the wind turbine operation information under different scenarios. The simulation results are investigated to reveal the influence of the FSI phenomenon on wind turbine performance. Analysis of wind turbine aeroelastic stability is conducted to prevent blade from experiencing flutter problem. A multiple objective optimization method for wind turbine design including aerodynamic and structure has been developed to improve wind turbine performance. The flow field analysis results showed that the strength of vortex at the tip and root of the blade increases as wind speed increases when wind turbine is under operating conditions. With wind speed of 10m⁄s, most of the flow over the lower surface remains attached and the wind turbine blade was running under design condition. As the wind speed increases, flow separation emerges. When the wind speed increasing to 16m⁄s, the wind turbine blade works under deep stall condition. The wind turbine power coefficient drops continuously from 0.46 to 0.22, as wind speed increased from 10m⁄s to 20m⁄s. The comparison of wind turbine power and torque coefficient under different CFD configuration shows the advantage of whole flow field analysis with hybrid turbulence model. The structural analysis results demonstrated that most of the pressure force acts at a region around the 1⁄4 chord from the leading edge of the blade under operating condition and the displacement of blade tip in flap direction is bigger than those in the other directions. Modal analysis results deduced that flap is the main type of vibration in first and second modes. The difference of natural frequency between single blade and blade rotor becomes larger as vibration order increases. The dynamic performances of wind turbine blade and rotor are totally different and show the whole flow field method is better than the one third domain method. The wind turbine aeroelastic analysis results illustrate that the bending frequency and torsion frequency are around 23.94Hz and 38.46Hz respectively under TSR=4 and both move towards 30Hz under TSR=1.7. When TSR is smaller than 1.7 the wind turbine will experience flutter due to the overlapping of bending and torsion frequencies. The multiple objectives optimization method takes the aerodynamic performance and blade loading into account to gain better design parameter. The comparison between initial and optimal design shows that optimized method could provide higher electrical energy around 1073kW•h per annum under rated wind speed. The optimized wind turbine critical flutter wind speed will increase from initial design speed of 35m/s to 38m/s under optimization design.

I.IntroductionThe vertical axis wind turbine has been widely concerned because of its advantages such as multiphase wind, stable force, easy installation and maintenance, and small starting wind speed. Vertical axis wind turbines mostly use permanent magnet synchronous generators or doubly fed induction wind turbines, and most of them are axial flux permanent magnet generators[1]. Compared with doubly fed induction wind turbine, permanent magnet synchronous generator (PMSG) has the advantage of high power density and is the main research object of vertical axis wind turbine. However, the direct coupling of the high power axial flux permanent magnet synchronous generator and wind turbine causes the starting of the wind turbine to become more difficult. In order to improve the starting performance of vertical axis wind turbines, maglev technology is considered to reduce the starting resistance as the development direction of vertical axis wind turbines. Therefore, an asymmetric-primary axis-flux hybrid- electricity generator is proposed in this paper, and the decoupling control of levitation force and output power is implemented using asymmetric primary and hybrid excitation.II.operation principleThe proposed asymmetric-primary axis-flux hybrid-excitation generator for the vertical axis wind turbine structure is shown in the Fig.1.The generator is composed of double stator primary and single actuator. The double stator primary has an asymmetric structure design, and the rotor shaft is connected with the wind turbine shaft to realize direct drive wind power generation. The rotor adopts the spacing design of permanent magnet and modulating tooth to reduce the consumption of permanent magnet. Both the excitation winding and the armature winding are located in the primary stator, so the mixed excitation and magnetic field can be adjusted without adding any mechanism such as brush slip ring, which reduces the complexity of the structure.In general, the proposed generator has the following characteristics(1) The flat structure shortens the axial length of the generator and is suitable for direct drive of vertical axis wind power generation system.(2) The levitation force is provided by bilateral unbalance design of axial flux. The two sides adopt different primary sizes, and then the axial electromagnetic force imbalance of the bilateral air gap forms the suspension force, which avoids adding active and passive levitation mechanisms and reduces the complexity of the overall system.(3) The levitation force and output power are controlled by hybrid excitation. The primary tooth DC excitation is adopted to realize zero crosslinking of the excitation with permanent magnet and armature, and the levitation force regulation does not affect the output power. The system can start at low wind speed, and the levitation force and total output power can be adjusted according to the change of wind speed. Through free distribution of bilateral power to achieve the total power following the wind speed and the levitation force following the lift force of the wind turbine.(4) Using magnetic field modulated axial magnetic field structure, the rotor structure is simple and reliable. If the pole pair numbers of rotor and armature are pr and ps, and the number of the stator tooth is pn, there is pr = pn±ps. The design makes it have the magnetic field modulation effect, which can increase the magnetic field change rate under the low speed, thus increasing the generation power.(5) The use of concentrated armature windings and excitation windings reduces the end, thus reducing magnetic leakage and losses.III.simulation and resultsA three-dimensional finite element model of the asymmetric-primary axis-flux hybrid-excitation generator is established, and the no-load characteristics and load characteristics of the generator are obtained. The no-load characteristics under different excitation current are simulated, and the flux linkage of armature coils and DC excitation coils are shown in Fig.2.We can see that when different excitation currents are applied, the crossing flux linkage between DC excitation winding and secondary permanent magnet is almost 0, and DC flux has little effect on the armature flux. Therefore, When the excitation changes, the unilateral levitation force changes only in amplitude, but there is no harmonic phase shift, and positioning torque is almost unaffected. he proposed generator has good decoupling performance of levitation force, output power, and DC excitation. In addition, the optimization design of the generator is further studied such as pole arc coefficient, positioning moment and pole slot ratio. IV.conclusionIn this paper, we proposed an asymmetric-primary axis-flux hybrid-excitation generator, studied the no-load characteristics, load characteristics and excitation characteristics, and optimized the structural parameters of the generator. The simulation results are obtained, and state that the generator can realize the decoupling of the levitation force of excitation and power, which is suitable for vertical axis wind turbine. **

A vertical-axis wind turbine (VAWT) is a type of wind turbine where the main rotor shaft is set transverse to the wind (but not necessarily vertically) while the main components are located at the base of the turbine. The performance of a Vertical Axis Wind Turbine (VAWT) is closely related to its Tip Speed Ratio (TSR). It is not easy to know beforehand which TSR will result in maximum power extracted from the VAWT. The objective is to model and simulate a 2D H-type VAWT in an open-source OpenFOAM CFD solver. The turbulence model used is k-Omega SST (Shear Stress Transport), and the rotating domain is set up using Arbitrary Mesh Interface (AMI) and dynamicMeshDict in OpenFOAM. Due to the transient nature of the simulation, pimpleFoam solver is used to simulate VAWT. Forces and Moments are reported after certain timesteps to obtain the torque Vs. Time curve for different TSRs. The simulation is carried out for different TSRs, and the graph of Coefficient of Power (Cp) Vs. TSR is plotted. It is found that the Cp first increases with an increase in TSR up to 0.35, and then Cp decreases. Such type of analyses can be used as a low-cost basis to obtain boundary and initial conditions or obtain baseline input parameters for 3D simulation of VAWTs.

Slotted airfoils mitigate the flow separation on the blades operating at high angles of attack in the upwind region, consequently augmenting the power coefficient and reducing the startup wind speed of Darrieus vertical axis wind turbines (VAWTs). Nonetheless, the presence of the slot structure alters the original flow dynamics, inducing flow separation when the blade operates in the downwind region and at elevated blade tip speed ratios (TSR), which leads to a reduction in the blade’s power coefficient. This study establishes an aerodynamic model of the flow field migration around the blade surface by utilizing the lattice Boltzmann method in conjunction with large eddy simulation to ascertain the influence of the inlet and outlet positions of the slot on the flow field structure across different wind regions. The simulations indicate that, under the downwind region and at high TSR, positioning the slot at the midsection of the blade, although it expands flow separation near the trailing-edge, does not disrupt the primary flow at the leading-edge. Unexpectedly, the slot optimizes the pressure distribution on the pressure side of the blade, thereby enhancing the blade’s performance in the downwind region. At a TSR of 3.3, the average power coefficient of the blades in the downwind region increases by up to 63.62%. These results offer valuable insights for the implementation of slotted airfoils to enhance energy conversion efficiency in VAWTs’ design optimization.

Improving the self-starting and operating characteristics of vertical axis wind turbine by changing center distance in part of blades

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

Numerical simulations of a micro scale vertical axis wind turbine (VAWT) rotating at constant speed were performed with steady and unsteady wind conditions. The aim of the study was to determine both the performance of a VAWT in unsteady wind conditions and also to determine the flow physics that causes the performance. Frequencies used for the unsteady incoming wind ranged from high values equal to the VAWT rotational frequency to low rates of up to an order of magnitude slower. Mean and standard deviation of wind velocity data from a local wind station were used as mean and amplitude of the variation in wind speed. In general the results show a decrease in performance versus steady wind conditions. The worst cases show a 75% drop in power coefficient (CP) for wind fluctuation rates equal to a quarter of and an order lower to the VAWT rotational frequency. Increasing wind velocities induced earlier stalling and loss of lift on VAWT blades while decreasing wind velocities reduced the apparent angle of attack and subsequently the lift generated by the blades. A hysteresis in the CP was observed when the VAWT was in the low tip speed ratio (λ) region while negative performance dominated the high λ region. For the conditions tested here, any time variation in the wind tends to decrease the energy yield of a VAWT.

In South East Asia countries such Malaysia, wind turbine is generally not suitable to be used in large scale to generate electricity due to inconsistent wind speed and suitable land site availability. However, a small scale application is of preference as the wind speed in the region lies within the low speed range of approximately 2-5 ms−1 with intermittent highs up to 8 ms−1. The performance of Vertical Axis Wind Turbines (VAWTs) is known to be better compared to Horizontal Axis Wind Turbines (HAWTs) in urban conditions due to its omnidirectionality, which allows it to operate in fluctuating turbulent wind conditions. However, the major drawback of VAWTs is the inability to self-start under low wind speed conditions. Hence, the objective of this work is to investigate the Pivoting Panel Mechanism (PPM) which aims to assist VAWT models to self-start at low wind speed condition. Three sets of PPM width configurations (70mm, 80mm, 90mm) are used to study the effect of increasing the pivot panel surface area on the VAWT performance. Performance test showed that the PPM model improved the power coefficient values at the tip wind speed range of TSR<0.75 (PPM 70mm>80mm>90mm). Further investigation revealed that the larger PPM surface area (90mm) was able to assist the VAWT model to achieve a shorter RPM response time at wind speed of v = 2.5ms−1 and 2.9ms−1. These findings have considerable implications for future researches for the optimization of PPM design parameters and its adaptations in VAWT turbine design.

The release of carbon emissions and other pollutants resulting from the combustion of fossil fuels constitutes a significant environmental challenge. Throughout the years, numerous initiatives have been undertaken to mitigate or diminish these emissions, notably through the adoption of renewable energy sources as viable alternatives. Wind energy is classified as a renewable energy source that is harnessed through wind turbines to transform wind energy into mechanical and electrical energy. Wind turbines exhibit a diverse array of types, designs, and dimensions. Nevertheless, such designs and their corresponding types encounter various challenges, which include, but are not limited to, inadequate starting capabilities, suboptimal efficiency, and a propensity for unidirectional wind acceptance (specifically about horizontal axis wind turbines). In response to these challenges, this paper delineates the design and simulation of a dual-rotor, two-stage hybrid vertical axis wind turbine (DRDSH VAWT) intended for small-scale power generation. The DRDSH turbine is comprised of a 3-blade modified Savonius Bach-type rotor in conjunction with a 3-blade two-stage Darrieus turbine. Computational fluid dynamics (CFD) simulation models are employed to analyze and evaluate the performance of the turbine. The findings of the study indicated that the power coefficient (CP) of the DRDSH VAWT experienced a 71.4% increase at a tip speed ratio (TSR) of 0.563 in comparison to a 3-bladed dual rotor conventional vertical axis wind turbine (DRC VAWT). Additionally, the moment coefficient (cm) of the DRDSH VAWT exhibited a 55.2% increase at a TSR of 0.560 relative to the DRC VAWT. The DRDSH VAWT also generated 35.8% more power than the DRC VAWT, demonstrating a direct correlation between wind speed and power output. Furthermore, this indicates that the CP of the DRDSH VAWT improved by 63.7% with increasing wind speed when compared to the DRC VAWT. CFD analysis revealed that the turbine is optimally suited for lower TSRs. During the initiation phase, a practical and efficient switching mechanism was integrated to facilitate the assistance of the Bach-type rotor to the DRDSH VAWT, thereby enhancing the efficiency of the turbine.

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.

This paper discusses the design of a low tip-speed ratio, drag type vertical axis wind turbine which is incorporated with permanent magnet synchronous generator with maximum power point tracking (MPPT) strategy of control system to acquire the optimal performance. By using two dimensional large eddy simulations (LES) method as fluid dynamic model, the calculated power coefficient for this multi-blade vertical axis wind turbine may reach 0.34 at tip speed ratio (TSR) ranging from 0.8 to 1.0. Also, with the aids of simulation results, a direct coupled permanent magnet synchronous generator with 64-poles is designed and fabricated to generate 1.5 kW rated power at 90 rpm in 12 m/s wind speed. By changing the shape of magnet and applying approximate-skew method as stepped magnet configuration, the cogging torque and noise level of generator can be minimized. Moreover, MPPT control system with low current harmonic distortion level is designed to transfer energy into power grid with estimated 92% of power efficiency. Consequently, by eliminating gearbox system, low start-up wind speed, low current harmonic distortion and low cogging torque, the proposed of low acoustic/noise level wind turbine generator system can be applied for urban-environmental usage.