Self-starting Performance Research Articles

Study on a novel dual-row vertical axis wind turbine with J-Shaped blades by using numerical methods and optimization

ABSTRACT This study investigates the benefits of using J-shaped blades in a dual-row Darrieus wind turbine (DDWT), combining two innovative ideas whose simultaneous impact on the self-starting capability of Darrieus turbines has not been explored. The performance of the turbine was simulated using Computational Fluid Dynamics (CFD) and optimized using both the Taguchi method and a combined Machine Learning and Genetic Algorithm (ML-GA) technique. Three main operating parameters, including the tip speed ratio (λ), radial ratio (δ), and angular distance (ϕ) of dual-row turbines, were investigated across four levels using an L25 orthogonal array design. According to the Taguchi analysis, the impact of the parameters on the power output was ranked in the order of λ > δ > ϕ. After comparison, the optimized turbine predicted by the ML-GA technique was chosen due to the superior accuracy of the ML-GA approach compared to the Taguchi method. The optimal configuration of a DDWT with J-shaped blades was predicted at λ = 2.15, δ = 1.39, and ϕ = 75.36, with a Cp of 0.49 based on CFD simulations. Compared to the single-row wind turbine, the proposed turbine showed a significant increase of the Cp at low tip speed ratios resulting in a better self-starting performance.

Numerical investigation of the impact of the diameter and rotational motion of a multi-blade rotor on the hydrokinetic combined turbine performance

The vertical axis combined hydrokinetic turbine (VACHT) presents promising applications in marine environments due to its high self-starting performance and efficiency. However, traditional VACHTs suffer from significant performance losses in the outer rotor when the diameter ratio is large and the startup dead zone issue of the inner Savonius rotor. To address these challenges, this study proposes a VACHT composed of an H-type rotor and a multi-blade (M-type) rotor, categorized into two structures based on counter-rotating and co-rotating operations. Numerical simulations reveal that the diameter ratio (f) has a greater impact on VACHT performance than the tip speed ratio. Counter-rotating allows the VACHTs to accommodate larger diameter ratios (f > 0.6) than co-rotation. The diameter ratio primarily influences the interference between the inner and outer rotors. The M-type rotor enhances the self-starting performance of both VACHTs, providing enhancements exceeding 200 %. Moreover, cluster arrangements of VACHTs benefit from increased power output due to enhanced blockage effects, with co-rotating VACHTs exhibiting higher gains (13.65 %) compared to counter-rotating VACHTs (9.84 %). The lengths of both VACHTs’ wake are similar to H-type turbines, indicating that the compactness of the VACHT cluster remains unaffected.

Prediction model for self-starting of hypersonic inlets with soft critical unstart mode

The acceleration self-starting performance of hypersonic inlets is of critical importance for the stable operation of scramjet engines. The occurrence of soft unstart during the transition from hard unstart to start is an important flow state that has yet to be fully elucidated. The stability mechanism and corresponding self-starting characteristics of soft unstart remain poorly understood, and there is a pressing need for detailed modeling research in this area. This paper presents a rapid prediction model for the self-starting Mach number of two-dimensional hypersonic inlets with soft critical unstart mode, fully considering the influence of various geometric parameters and Reynolds number in the internal contraction section, and achieving a quantitative analysis of the two-dimensional soft unstart critical flow field. Given the incoming flow conditions and the inlet geometry, the prediction model is capable of accurately representing the actual viscous unstart flow field. It can fully map the unstart separation bubble and its surrounding critical wave structures, and calculate the minimum pressure rise required to maintain the current scale of the main separation bubble and the pressure rise exerted on the unstart separation bubble by the current actual flow field structure. Comparing the relative magnitude of these two pressures determines whether the inlet can transition from soft unstart to start. The proposed prediction model was validated using results from unsteady numerical simulations. The predicted results align well with the simulation results and are significantly better than previous prediction methods.

A Study on the Effect of Turbulence Intensity on Dual Vertical-Axis Wind Turbine Aerodynamic Performance

Examining dual vertical-axis wind turbines (VAWTs) across various turbulence scenarios is crucial for advancing the efficiency of urban energy generation and promoting sustainable development. This study introduces a novel approach by employing two-dimensional numerical analysis through computational fluid dynamics (CFD) software to investigate the performance of VAWTs under varying turbulence intensity conditions, a topic that has been relatively unexplored in existing research. The analysis focuses on the self-starting capabilities and the effective utilization of wind energy, which are key factors in urban wind turbine deployment. The results reveal that while the impact of increased turbulence intensity on the self-starting performance of VAWTs is modest, there is a significant improvement in wind energy utilization within a specific turbulence range, leading to an average power increase of 1.41%. This phenomenon is attributed to the more complex flow field induced by heightened turbulence intensity, which delays the onset of dynamic stall through non-uniform aerodynamic excitation of the blade boundary layer. Additionally, the inherent interaction among VAWTs contributes to enhanced turbine output power. However, this study also highlights the trade-off between increased power and the potential for significant fatigue issues in the turbine rotor. These findings provide new insights into the optimal deployment of VAWTs in urban environments, offering practical recommendations for maximizing energy efficiency while mitigating fatigue-related risks.

Coupled dynamic response and energy conversion characteristics of 10 MW floating vertical axis wind turbine with different configurations

Vertical axis wind turbines (VAWTs) are superior because they have compact structure, good wind adaptability and strong scalability. The coupling dynamic response mechanisms between different configurations of wind turbines and floating platforms are different. Based on the CFD method, dynamic fluid body interaction (DFBI), overlapping grid and dynamic grid techniques are used for numerical simulations. The force characteristics and self-starting features of H-type and Φ-type VAWTs are compared. The aerodynamic performance and motion response of the floating VAWT (FVAWT) are studied under different tip-speed ratios (TSR) and aspect ratios (η). The results show that the power coefficient (Cp) of H-type and Φ-type FVAWTs reaches the peak when TSR = 6 and TSR = 7, respectively. The optimal η for both is 1.2. The H-type FVAWT improves the Cp by 34.3% compared to Φ-type FVAWT. H-type FVAWT has a large thrust and excellent stability. The Φ-type FVAWT requires less initial thrust, and the self-starting performance is 12% superior to H-type FVAWT. With the increase of TSR and η, the heave motion of both FVAWTs is almost unaffected, but the pitch motion sensitivity is stronger. The heave amplitude of H-type FVAWT is 282% larger than Φ-type FVAWT, which has a gain effect on energy conversion. The Φ-type FVAWT has better safety. The strengthened structure of Φ-type VAWT has a noticeable impact on velocity and vortex distribution. In addition, the aerodynamic and hydrodynamic performance of the FVAWT is improved.

Exploring the impact of flexible membranes on the performance of H- and S-type hydrokinetic turbines: An experimental investigation

Vertical axis hydrokinetic turbines (VAHTs) have the potential to harness deep-sea current energy without the need for a yaw mechanism. However, H-VAHTs have weak self-starting capabilities, and S-VAHTs also face startup dead point issues. To address the self-starting challenges of VAHTs, this study proposes attaching flexible membranes to the blades of VAHTs. The impact of flexible membranes on the performance of both types of VAHTs is evaluated through Particle Image Velocimetry (PIV) water flume experiments. The results demonstrate that attaching flexible membranes to the blade surfaces resolves the self-starting dead point issue for both turbines, with a greater improvement in self-starting performance for H-VAHTs than for S-VAHTs. The study found that for both turbines, attaching flexible membranes with a large opening on the blade’s outer side offers the best self-starting performance and power output. However, the flexible membranes reduced the CP of H-VAHTs, while slightly enhancing the performance of S-VAHTs. PIV tests showed that the flexible membranes form a cup-shaped structure when facing the flow. The pressure difference between the inside and outside of the membranes generates additional static torque, improving the self-starting performance of both turbines. Furthermore, even with one or two membrane blades missing, the self-starting capability of H-VAHTs was still enhanced; flexible membranes with a certain installation angle can also be attached to the endplates of S-VAHTs to address startup dead issues. In summary, attaching flexible membranes to VAHTs improves their self-starting performance and ensures power output, thereby facilitating the application of such turbines in deep-sea areas with low flow velocities.

Study of the Self-starting Performance of a Vertical-axis Wind Turbine

Study of the Self-starting Performance of a Vertical-axis Wind Turbine

Generalized prediction for self-starting performance of two-dimensional hypersonic inlets

The acceleration self-starting performance of a hypersonic inlet is pivotal for ensuring the stable operation of a scramjet. While the geometric configuration of the internal contraction section (ICS) considerably influences the inlet's self-starting performance, the current prediction model solely considers the internal contraction ratio. To encompass the entire geometric configuration's influence on ICS, a generalized prediction model for the acceleration self-starting Mach number of critical hard unstart two-dimensional hypersonic inlets is proposed. This model calculates the theoretical reattachment pressure rise of the main separation bubble within the actual unstarted flow structure of the hypersonic inlet. Additionally, it computes the theoretical pressure rise assuming the main separation bubble is in a critical state. By comparing these pressures, the model evaluates whether the main separation bubble can be sustained under given incoming flow conditions, predicting the self-starting Mach number. This modeling approach offers broad adaptability to various ICS configurations and incoming flow Reynolds numbers. Each step of the prediction model and the final computational results underwent rigorous evaluation through unsteady numerical simulations. Remarkably, the prediction results demonstrated exceptional alignment with simulation outcomes, surpassing the accuracy of previous prediction methods.

Structural analysis of wind booster for multistorey vertical axis wind turbine

Wind energy is optimistically looked upon as potent alternative source of energy. Vertical axis wind turbines are developed and commissioned to cater for the large scale and domestic power requirements. The self-starting torque of a vertical axis wind turbine is augmented by using an enclosure known as a wind booster. An innovative wind booster has been designed to improve the self-starting performance of vertical-axis wind turbines. The edifice of the vertical axis wind turbine has to sustain high-magnitude wind gusts during its entire life cycle. The wind boosters should be designed to sustain the anticipated high-magnitude wind gust. In this research work, structural analysis of Wind booster is conducted to analyze deflection and maximum stress. Modal analysis of the wind booster was conducted to understand the behavior of the wind booster at different frequencies. ANSYS-SAMCEF software is used for entire numerical analysis. Von Misses stress model is used to estimate the maximum and minimum stress. The maximum stress induced in vertical deflectors is 4.64 MPa, wherein the maximum defection is 9.75 × 10−3. Analytical and numerical analysis of wind booster deflectors has been done for Von Misses stress and it is found to be in close agreement with other.

Power performance and self-starting features of H-rotor and helical vertical axis wind turbines with different airfoils in turbulence

Wind tunnel tests were conducted to systematically assess the aerodynamic performance of both H-rotor and helical vertical axis wind turbines (VAWTs) in smooth and turbulent flows. The effects of airfoil section and pitch angle β on the power and self-starting performance were examined for both types of turbines. The helical turbine had a wider operating range of tip speed ratios (TSR λ) and much lower power performance than its H-rotor counterpart. This phenomenon was attributed to the flow deflection of helical blades due to their three-dimensional features, as well as that dynamic stall of a helical blade would not occur simultaneously for all blade elements. The helical turbine did not exhibit notably improved self-starting performance despite of the high manufacturing cost. Moreover, the start-up process was analyzed by using the static torque coefficient CT of both single-bladed and three-bladed turbines. It was found that turbulence intensity exercised a significant impact on CT. Turbulence would cause serious fatigue issues for H-rotor turbines and change the driving mechanism of helical turbines though it enhanced the self-starting performance. Recommendations were finally provided for the design of VAWTs in built environments.

Novel hybrid blade design and its impact on the overall and self-starting performance of a three-dimensional H-type Darrieus wind turbine

The present study proposes a novel hybrid blade design that is the combination of a conventional airfoil, namely the NACA0018, and its J-shaped profile to increase the torque generation at the start-up stage of the turbine while decreasing the potential efficiency loss at the high tip speed ratios. Therefore, a new 2D-based design methodology was proposed, and depending on this methodology, different hybrid blade configurations were determined for the investigation of the overall and self-starting performance of the H-type Darrieus vertical axis wind turbine. Due to the inherent shape of the proposed hybrid blade, a 3D CFD dynamic start-up model, which is based on the fluid–turbine​ interaction, was built and used to evaluate the performance of the different configurations of the hybrid blades. The results indicate that although the proposed design methodology is based on the 2D-CFD calculations, it enables a quicker prediction of the aerodynamic performance of the proposed hybrid blades compared to the 3D-based CFD simulations. Furthermore, the findings also clearly illustrate that the new proposed hybrid blade designs not only overcome the self-starting issue of the turbine but also provide a wider turbine operating range and an improvement in the turbine peak efficiency in contrast to the losses caused by J-shaped airfoils.

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

Compared with the horizontal axis wind turbine (HAWT), the vertical axis wind turbine (VAWT) has the advantages of low noise operation and no wind yaw device. However, the poor self-starting performance of VAWT is one of key problems restricting its development. In order to improve the self-starting capability of VAWTs in urban wind areas, this paper proposed a VAWT model with multi-blade local variable radius. The main object of this study is to research the effect of reducing the partial blade radius on the self-starting performance and power coefficient of the VAWT. In this study, the partial blade radius of the VAWT models was reduced to 0.375, 0.5, and 0.625 times of the outer layer. The dynamic torques and velocity contours of the different models were researched by experiments and numerical simulations to analyze the reason why reducing the partial blade radius affects the power coefficient of the VAWT. The static torque and static pressure contours of different models were researched to compare the self-starting capability of the models. According to the results, the minimum static torque values of the three innovative VAWT models were increased by 0.1, 1.8, and 2.8 times, respectively, compared to the traditional VAWT with only the outer layer. Furthermore, the power coefficients of three models were increased for tip speed ratios (TSR) less than 2.2. Therefore, the new models can improve the self-starting capability of VAWTs, and the higher power coefficients at low TSRs make them more advantageous for applications in urban buildings and low wind speed areas.

Assisting the mode-locking of a figure-9 fiber laser by thermal nonlinearity of graphene-decorated microfiber.

The self-starting performance of a figure-9 fiber laser is critically dependent on the phase shift difference between the counter-propagating beams. Herein, we propose an effective approach to dynamically control the phase shift difference in a figure-9 fiber laser by utilizing the thermal nonlinearity of graphene-decorated microfiber device. With the adjustment of the control laser power injected into the graphene-decorated microfiber, the self-starting mode-locked threshold of the figure-9 fiber laser can be attained in a flexible pump power range, i.e., from 300 mW to 390 mW. These findings demonstrated that the graphene-decorated microfiber could act as a dynamical control device of phase shift difference for improving the performance of figure-9 fiber lasers, and might also open up new possibilities for applications of microfiber photonic devices in the field of ultrafast optics.

Numerical Experiments on Hydrodynamic Performance and the Wake of a Self-Starting Vertical Axis Tidal Turbine Array

In this paper, based on the CFD software ANSYS-Fluent, two-dimensional numerical models are established to investigate the hydrodynamic performance of a self-starting H-Darrius vertical axis tidal turbine (VATT) array of three turbines in a triangular layout with 3D in axial and radial distance. Three main aspects are explored in this study: (1) the self-starting performance, power coefficient, flow fields, and blade force of the double-row VATT array, which are compared with a stand-alone turbine, (2) the wake development of the front and rear displacement turbines, and (3) the feasibility of the double-row self-starting VATT array in practical applications. It is found that the power coefficients of the three turbines in the array all improved compared with that of the stand-alone turbine, and as the load increased, the difference between the averaged power coefficient of the array and a stand-alone turbine was more obvious, with a maximum difference of 3%. The main effects of the front turbines on the rear turbine are energy utilization and turbine vibration. Due to the beam effect between the front turbines, the incident flow rate of the rear turbine increased to approximately 1.2 times the free flow rate. However, the greater rotational fluctuations of the rear turbine mean that although it had a higher power factor, it was more susceptible to fatigue damage. The wake of the rear turbine in the array had a much larger area of influence on both the length and width, but the velocity deficit recovered more quickly to over 95% at a distance of 10D behind it. The rate of wake velocity recovery is load-dependent for a stand-alone self-starting turbine, but this was not evident in the arrays. The positive torque of the turbine is mainly generated when the blade rotates through an azimuth angle from 45° to 160° and mainly benefits from the inner side of the blade. For the double-row three-turbine array, the axial and radial spacing of 3D is reasonable in practical applications.

Aerodynamic Performance Analysis of Adaptive Drag-Lift Hybrid Type Vertical Axis Wind Turbine

In recent years, with the continuous development of new energy, how to efficiently use wind energy has received more and more market attention. Due to cost advantages, the development of small wind turbines is accelerating. Among them, the design and research of the airfoil design and research of the lift vertical axis wind turbine has matured, but because of the aerodynamic characteristics of the lift airfoil structure, it is impossible to start itself at low wind speed, resulting in the waste of low wind speed energy. Although the drag wind turbine has good self-starting performance, the wind energy utilization efficiency in the high-speed state is inefficient. Each has its own unique shortcomings, which directly affects the marketization of small wind turbines. In order to solve these problems, this paper presents a drag-lift hybrid type wind turbine structure based on an NACA0018 symmetrical airfoil, which can adaptively change the blade shape. This design can keep the blade in the drag shape under static and low speed conditions, and adaptively change the lift shape with the increase of speed. In addition, through the research method of CFD numerical simulation combined with physical experiments, the proposed wind turbine design is studied and analyzed from multiple angles. At the same time, the “6DOF + dynamic grid” setting is used to study the influence of the opening angle factor of the drag-lift hybrid blade on the self-starting performance, and the study shows that the design of the drag-lift hybrid blade proposed in this paper has a higher self-starting torque and lower starting wind speed than the traditional lifting blade, and it is observed that the drag-lift hybrid blade has the best self-starting performance when the opening angle of the blade is 80°. At the same time, the problem of switching the blade morphology of the drag-lift hybrid blade is also analyzed, along with how to use the spring to control all this adaptively. In order to better analyze the advantages of the drag-lift hybrid design proposed in this paper, a wind tunnel test was also carried out using the physical model, and the relationship between the leaf tip speed ratio and the wind energy utilization rate was obtained, which intuitively showed the improvement of the wind energy utilization rate of the drag-lift hybrid design compared with the traditional lift blade.

Geometric design optimization of a Savonius wind turbine

Savonius vertical-axis wind turbines are becoming an outstanding alternative for small-scale power generation mainly due to their simple design, high self-starting performance at low wind speeds, omnidirectional capability, and low cost. Over the past few decades, extensive research has suggested turbine configurations that maximize their aerodynamic performance, evaluating different influencing geometric parameters. Nevertheless, few studies have considered running large-scale experimentation, simultaneously assessing different influencing parameters, and implementing mathematical optimization techniques. Consequently, there is a need to establish a set of procedures and techniques that address these gaps. The current research proposes a new design method for a Savonius wind turbine to maximize its aerodynamic performance. The proposed method defines a numerical model for a geometry with four influencing parameters, which automatically achieves solutions to the equations that govern the motion of fluids for different turbines. The model is successfully validated with experimental results available in the literature. The numerical solutions of 340 different turbines build a response surface with excellent quality metrics based on the Kriging technique. Two mathematical optimization techniques are implemented on the response surface to determine the configuration that maximizes its aerodynamic performance. This optimal configuration is characterized under different operating conditions. The results indicate that the optimal turbine has an aspect ratio of 8.38, an overlap ratio of 0.08, a twist angle of 174.05°, and two blades. The behavior shown by the optimal turbine (maximum power coefficient of 0.21 at a wind speed of 12 m/s) is remarkable since its aerodynamic performance is superior to multiple reported turbines. The instantaneous torque that it develops is always positive during its operation, which indicates a greater capacity for self-starting and continuity in its rotation. Likewise, it supplies a maximum rotor power of approximately 160 W at a wind speed of 12 m/s. These results make the optimal turbine an attractive design for electric power generation. The proposed method provides novel insights and powerful tools for researchers to explore various geometries and operating conditions that, together with the established optimization process, accomplish the turbine that maximizes its aerodynamic performance.

Study on Aerodynamic Performance of a Straight-Bladed VAWT Using a Wind-Gathering Device With Polyline Hexagonal Pyramid Shape

The self-starting performance and aerodynamic characteristics at low wind speeds are the two main problems for the straight-bladed vertical Axis wind turbine (SB-VAWT). In this study, a new kind of wind-gathering device (WGD), which can be installed up and down the rotor, with a polyline hexagonal pyramid shape, was proposed. Both the numerical simulation and the wind tunnel test were performed on this WGD. Based on the method of quadratic rotary orthogonal combination design, the effect of the main structural parameters of the WGD on the self-starting performance of the SB-VAWT was researched by 3D numerical simulation. The optimal combination of the main structural parameters for the WGD under the condition of this study was obtained. Furthermore, wind tunnel tests were carried out on the SB-VAWT with and without the WGD having the optimal structural parameters, including the starting performance, power performance, and rotational revolution performance. The results showed that both the static performance and dynamic performance of the SB-VAWT were increased to some degree by installing this kind of WGD. The improvement is more obvious under the condition of low wind speed. This research can be a useful reference for the in-depth study on the optimal WGDs for the SB-VAWTs.

Unjuk Kerja Performa Turbin Arus Laut Sumbu Vertikal Pada Berbagai Bentuk Sudu Unik

Efficiency and self-starting capability performances are the main problems in vertical axis turbines. By purposing improves its performance, vertical axis turbines have been developed with various models. One of the developments of this model is to design the turbine blades into unique shapes. This research aims to determine the performance of some unique blade vertical axis turbines conditioned on the same parameters, especially if applied in a marine environment. Turbines with helical blade (HB), eggbeater-shaped blade (ESB), diamond-shaped blade (DSB), Y-shaped blade (YSB), and arrow-shaped blade (ASB) were investigated based on efficiency and self-starting capability using QBlade software. Good performance symmetrical foils such as NACA 634021 are also applied to each turbine. The simulation results show that from the aspect of efficiency performance, turbine ASB > HB > ESB > DSB > YSB. Meanwhile, in the aspect of self-starting capability performance, the sequence is similar to efficiency performance, based on the two approaches applied. The highest efficiency achieved by the ASB turbine is 0.391 at the lowest tip speed ratio of λ = 4. The ASB turbine also achieves the best self-starting performance, which has a minimum static torque coefficient of 0.00155 and can produce the required power at the lowest marine current speed of 0.806 m/s. This performance brings the ASB turbine to produce a rated power of 52.52 kW, or more than twice the power production of the lowest efficiency turbine and has an average power gain of 3.75 kW per 0.2 m/s.

Study on Variable Geometry Scheme of High Mach Axisymmetric Inlet

For scramjet, the inlet plays the role of capturing airflow, pressurizing and decelerating the airflow, and providing supersonic airflow to meet the combustion requirements for the downstream combustion chamber. In this paper, a prototype inlet is designed by using the method of spiral characteristic lines, and then the influence of moving center cone on the inlet performance is studied by numerical simulation. It can be found that the method of moving the center cone can obviously improve the performance of non-design point and self-starting performance of the inlet.

Hydrodynamic performance of vertical axis hydrokinetic turbine based on Taguchi method

Hydropower generation is an important part of global renewable energy development. The vertical axis hydrokinetic turbine (VAHT) is a typical device to capture the kinetic energy of water. The optimization of its hydrodynamic performance can improve power coefficient. In this study, the Taguchi method was used to optimize the typical parameters of the vertical axis turbine, i.e., airfoil (NACA), pitch angle (β), enwinding ratio (ϖ), solidity ratio (σ), and small shaft position (O). An orthogonal array with five parameters and four levels was established; then, sixteen runs were simulated using computational fluid dynamics (CFD) software. A signal-to-noise (S/N) ratio analysis of the CFD simulation results was carried out, and the hydrodynamic performance of the optimized VAHT was studied. The results show that the influence strength order of each parameter on the power coefficient of the VAHT is featured by the relation NACA >σ > O > ϖ > β. According to the S/N ratio, the optimal combination of the five factors is as follows: NACA = 0020, β = 0°, ϖ = 1.25, σ = 0.382, and O = 0.5. In comparison with the initial design, the optimized minimum self-starting torque coefficient of the turbine is increased by 15.9%, which means that the self-starting performance is optimized. The power coefficient (CP) of optimized turbine is 0.1951, which is 17.59% higher than in the initial design, and the power coefficient fluctuation is 87.56% lower. Finally, the research findings could provide a reference for the optimal design of vertical axis turbines.