Values Of Tip Speed Ratio Research Articles

Effect of background turbulence on the wakes of horizontal-axis and vertical-axis wind turbines

We report a wind tunnel study on the wake generated by a horizontal-axis (HAWT) and a vertical-axis wind turbine (VAWT). Two scaled models, one of each type, have been tested in a wind tunnel, under low blockage and at Reynolds numbers, based on the rotor diameter D, of ReD=265×103 for the HAWT and 330×103 for the VAWT. The models scale with respect to the largest commercially deployed turbines is of 1/383 and 1/65.5, for the HAWT and the VAWT, respectively. Furthermore, two different inflows were tested: low and moderate turbulence conditions. For each type of turbine and inflow, different values of tip-speed ratio and ReD were tested.Hot-wire anemometry was used to characterize the wake at different streamwise positions, exploring the range 1<x/D<30 for the HAWT and 1<x/D<15 for the VAWT.We find that, under a low-turbulence inflow, both turbines generate significantly different wakes, characterized by the velocity deficit, wake width and the profiles of average and rms streamwise velocities. More specifically, in low-turbulence conditions, the VAWT presents faster recovery than the HAWT. Remarkably, we observe that a moderately turbulent inflow results in similar wake shapes for both turbines, presenting similar recovery and structure under all studied conditions.

Influence of the tip speed ratio on the wake dynamics and recovery of axial-flow turbines

Detached eddy simulation is employed to investigate the wake development downstream of the rotor of an axial-flow turbine and its dependence on the tip speed ratio. In this study, we found that the trend of the momentum deficit as a function of the rotational speed shows opposite directions in the near wake and further downstream. While the momentum deficit in the near wake increases with the rotational speed, it decreases further downstream. For instance, we found that at six diameters downstream of the rotor the streamwise velocity in its wake recovered to about 30% of its free-stream value at the lowest simulated tip speed ratio of 4, while its recovery was equal to about 65% at the largest tip speed ratio of 10. This is due to the earlier breakdown of the tip vortices. The results of the computations demonstrate indeed that mutual inductance phenomena between tip vortices, promoting pairing events and the eventual instability of the helical structures, occur at shorter downstream distances for higher values of tip speed ratio. Wake instability enhances the process of wake recovery, especially due to radial advection. Therefore, higher rotational speeds do not promote wake recovery through more intense tip vortices, but through their greater instability. Implications are important, affecting the optimal distance between rows of axial-flow turbines in array configurations: the operation at higher rotational speeds allows for smaller distances between turbines, decreasing the cost and environmental impact of farms consisting of several devices.

Performance estimation of small‐scale horizontal axis wind turbine blade

AbstractThe extracted energy from the wind is mainly influenced by the geometry of the rotor blades. Determining the aerodynamic optimum blade shape is one of the main tasks of the wind turbine designer. In the current study, the mixed airfoil technique was employed by using “Blade‐Element‐Momentum” (BEM) and “Computational‐Fluid‐Dynamics” (CFD) analysis to predict the aerodynamic performance of a small‐scale horizontal axis wind turbine blade. The BEM was then run using the open‐source wind turbine design and performance computation program Q‐Blade. The numerical simulation is carried out by Ansys Fluent. Here, the k‐ω Shear Stress Transport (SST) model was used. The results were compared with existing experimental data on lift and drag coefficients at the optimal angle of attack. The results of the two approaches were compared for different tip speed ratio values and a good agreement between CFD and BEM results was found.

Towards smart blades for vertical axis wind turbines: different airfoil shapes and tip speed ratios

Abstract. Future wind turbines will benefit from state-of-the-art technologies that allow them to not only operate efficiently in any environmental condition but also maximise the power output and cut the cost of energy production. Smart technology, based on morphing blades, is one of the promising tools that could make this possible. The present study serves as a first step towards designing morphing blades as functions of azimuthal angle and tip speed ratio for vertical axis wind turbines. The focus of this work is on individual and combined quasi-static analysis of three airfoil shape-defining parameters, namely the maximum thickness t/c and its chordwise position xt/c as well as the leading-edge radius index I. A total of 126 airfoils are generated for a single-blade H-type Darrieus turbine with a fixed blade and spoke connection point at c/2. The analysis is based on 630 high-fidelity transient 2D computational fluid dynamics (CFD) simulations previously validated with experiments. The results show that with increasing tip speed ratio the optimal maximum thickness decreases from 24 %c (percent of the airfoil chord length in metres) to 10 %c, its chordwise position shifts from 35 %c to 22.5 %c, while the corresponding leading-edge radius index remains at 4.5. The results show an average relative improvement of 0.46 and an average increase of nearly 0.06 in CP for all the values of tip speed ratio.

Clearance and blockage effects on hydrodynamic performance of hybrid hydrokinetic turbine

Hydrokinetic turbines are prominent solutions for providing electricity by utilizing the kinetic energy of flowing water streams. Various sites parameters such as flow velocity, channel dimensions and placement of turbine rotor across the water channel are the decisive factors to effectively harness the hydrokinetic energy. In current research, hybrid rotor is investigated considering different values of clearance and blockage ratio (by varying the channel dimensions). A hybrid rotor having the two conventional rotors (Savonius and Darrieus) is analyzed under different flow parameters such as flow velocity and tip speed ratio. To visualize the flow behavior across the turbine vicinity, flow contours have been analyzed and discussed. For the considered range of parameters, hybrid hydrokinetic rotor yields its maximum hydrodynamic performance corresponding to 0.55 value of clearance ratio. The maximum power coefficient as 0.122 occurs corresponding to 26.32% blockage ratio at 0.98 value of tip speed ratio (TSR).

Experimental study of a breastshot waterwheel with the degree of inclination of the nozzle spray against the tip speed ratio

The energy crisis is a severe problem facing the world, including Indonesia. Along with the times, innovation is needed to implement sustainable energy. Non-fossil energy sources have not been widely used, and efforts are still needed to utilize these energy sources. The waterwheel was the first device used in water production. One of the innovations for the sustainability of non-fossil energy is to make a waterwheel. There are still several waterwheels in Indonesia, but an investigation is needed to determine their condition. So in this study, investigating the breastshot water wheel uses a nozzle-based construction with variations in the degree of inclination of the spray against the TSR value. The results showed that the greater the inclination of the nozzle angle, the higher the velocity of the water flow when it enters the wheel. Adding water speed to this wheel will increase the momentum and tangential force. An increase in the tangential force will increase the wheel's torque so that the wheel strength will increase. This increase in power will, of course, result in greater efficiency, thereby increasing the tip speed ratio (TSR).

Analysis of tidal turbine blade loading due to blade scale flow

A blade element model is developed to include unsteady lift and drag coefficients and it is shown that this provides improved prediction of the spectrum of root bending moment of a tidal turbine blade for two definitions of onset turbulence. Computational Fluid Dynamics (CFD) is used to model the lift and drag forces on a 2D aerofoil using the relative onset flow from the different turbulence generation methods. Inclusion of the magnitude of high frequency fluctuations within the blade load spectra, results in an increased number of load cycles and improves prediction of Damage Equivalent Load (DEL). Discrepancy between prediction and existing experimental data is improved from 15% to within 2%. The signal-to-noise ratio (SNR) of relative velocity has been used to characterise the onset flow, and a relationship is established between onset flow conditions and the resultant fatigue loads (DEL). This has been applied to a number of onset conditions, typical of channel shear flows and upstream turbine wakes. For a given SNR, there is a 3.3 factor of variation in the DEL across the range of tip-speed-ratio (TSR) shown and over a single TSR value there is a 6.5 factor of variation across the DEL, over the largest range of SNR.

Effect of Blade Diameter on the Performance of Horizontal-Axis Ocean Current Turbine

The horizontal-axis ocean current turbine under investigation is a three-blade rotor that uses the flow of water to rotate its blade. The mechanical energy of a turbine is converted into electrical energy using a generator. The horizontal-axis ocean current turbine provides a nongrid robust and sustainable power source. In this study, the blade design is optimized to achieve higher efficiency, as the blade design of the hydrokinetic turbine has a considerable effect on its output efficiency. All the simulations of this turbine are performed on ANSYS software, based on the Reynolds Averaged Navier–Stokes (RANS) equations. Three-dimensional (CFD) simulations are then performed to evaluate the performance of the rotor at a steady state. To examine the turbine’s efficiency, the inner diameter of the rotor is varied in all three cases. The attained result concludes that the highest Cm value is about 0.24 J at a tip-speed ratio (TSR) of 0.8 at a constant speed of 0.7 m/s. From 1 TSR onward, a further decrease occurs in the power coefficient. That point indicates the optimum velocity at which maximum power exists. The pressure contour shows that maximum dynamic pressure exists at the convex side of the advancing blade. The value obtained at that place is −348 Pa for case 1. When the dynamic pressure increases, the power also increases. The same trend is observed for case 2 and case 3, with the same value of optimum TSR = 0.8.

The aerodynamic effects of blade pitch angle on small horizontal axis wind turbines

PurposeThe purpose of this paper is to thoroughly investigate the aerodynamic effects of blade pitch angle on small scaled horizontal axis wind turbines (HAWTs) using computational fluid dynamics (CFD) method to find out the sophisticated effects on the flow phenomena and power performance.Design/methodology/approachA small HAWT is used as a reference to validate the model and examine the aerodynamic effects. The blade pitch angle was varied between +2 and −6 degrees, angles which are critical for the reference wind turbine in terms of performance, and the CFD simulations were performed at different tip speed ratio values, λ = 2, 3, 4, 5, 6, 7, 9 and 10.5 to cover the effects in various conditions. Results are examined in two different aspects, namely, general performance and the flow physics.FindingsThe power performance varies significantly according to the tip speed ratio; the power coefficient increases up to a certain pitch angle at the design tip speed ratio (λ = 6); however, between λ = 2 and 4, the more the blade is pitched downwards, the larger is the power coefficient, the smaller is the thrust coefficient. Similarly, for tip speed ratios higher than λ = 8, the positive effect of the low pitch angles on the power coefficient at λ = 6 reverses. The flow separation location moves close to the leading edge at low tip speed ratios when the blade is pitched upwards and the also tip vortices become more intense. In conclusion, the pitch control can significantly contribute to the performance of small HAWTs depending on different conditions.Originality/valueIn the literature, only very little attention has been paid to the aerodynamic effects of pitch angle on HAWTs, and no such study is available about the effects on small HAWTs. The change of blade pitch angle was maintained at only one degree each time to capture even the smallest aerodynamic effects, and the results are presented in terms of the power performance and flow physics.

Pengaruh Sudut Sudu Turbin Jenis Taper Terhadap Tip Speed Ratio (TSR) dan Power Coefficient (CP) pada Turbin Angin Horisontal Berbasis Q-Blade

The utilization of wind energy as a power plant still needs to be improved by looking at the turbine performance, which is not always the same in different regional conditions. This study aims to determine the effect of the blade angle of the turbine on the tip speed ratio (TSR) and power coefficient (CP) by using a Q-Blade simulation. Q-Blade software can predict the value of the power generated at the blade rotation by comparing the CP and TSR values. The type of airfoil NACA 4412, taper blade, blade's numbers (4), blade radius (0.3 m), wind speed ± 3.6 m/s were fixed variables in this study. The simulation generated a graph of the relationship between CP and TSR changed and a simulation image of the load distribution ensued in the blade geometry. The blade angle of 30 at the TSR number 5 produced the highest CP values, which was ±0.4. The low loading value in the axis/rotor region, at a variation of the blade angle of 30, balances the centrifugal force on the rotating fluid. The centrifugal force produces thrust on the turbine so that the blade rotates with a high CP value in that area.

Comparison between two performance calculation methods applied for vawt

This paper presents a new model of 2D performance calculation applied to VAWT. The idea consist in considering only one blade to which a rotational oscillation motion is gave. Hence, the effect of the machine rotation and the influence of the rest of the machine on the focused blade are modelled. The study is purely numerical based upon the use of ANSYS-Fluent code to solve unsteady RANS equations, which follow from the new model. Several 2D geometry configurations of Darrieus machine were tested using the new approach and the results are compared to ones applied to the whole 2D rotor. A quasi concordance of the results is noticed for the overall predictions done from the two CFD methods. Although computational time is lower for the new model, tests reveal inadequate prediction of the peak's power coefficient and its Tip Speed Ratio value.

Pitch Angle Modulation of the Horizontal and Vertical Axes Wind Turbine Using Fuzzy Logic Control

The aim of this research work is to modulate the pitch angle of both types of wind turbines based on fuzzy logic control (FLC), as changes in the pitch angle have various functions in horizontal and vertical axis wind turbines. For HAWT, pitch angle control is applied to shield the electrical components of the turbine when the wind speed exceeds the rated speed without shutting down the turbine. FLC is used to control the angular velocity using two inputs and one output with three membership functions for both inputs and output. In VAWT, pitch angle control is applied to boost the performance of the turbine and its self-starting torque. FLC utilizes two inputs and one output with five membership functions for both inputs and output. For both turbine types, FLC produces a control signal that drives the actuator to achieve the desired pitch angle. The dynamics of HAWT and VAWT are simulated by the MATLAB/Simulink to demonstrate the influence of pitch controls on their dynamics. For HAWT, the FLC control has successfully maintained the angular speed of the rotor. The values of tip speed ratio and coefficient of performance are reduced in order to maintain the rotor angular velocity at its rated value. On the other hand, the results showed that the torque produced by the VAWT individual blade has improved with the pitch angle control. In addition, using FLC to control the pitch angle gives enhanced output and higher Cp at low tip speed ratios. Gain schedule PI controller is also used in both HAWT and VAWT for comparative study.

DESIGN MODELING OF SAVONIUS-DARRIEUS TURBINE FOR SEA CURRENT ELECTRIC POWER PLANT

Turbines convert the kinetic energy of ocean currents into electrical energy produced by the sea current electric power plant. This study aims to design a power generator turbine modeling that is carried out using the Computational Fluid Dynamic (CFD) approach by comparing the geometric performance based on the angle of attack and the Tip Speed Ratio (TSR) value of the Savonius-Darrieus Turbine. Having done several trials and errors during collecting the data, the value of the TSR 1.427; 2.853; 4.28; 5; and 5.7 is proposed. Here, the NACA 0018 series has been adopted on the current design of Savonius-Darrieus Turbine. The turbine has three blades, length of the span 357 mm, the diameter of turbine 428 mm, and length of the hydrofoil chord 40 mm. Effect of various angle of attacks from 0°up to 10° has been taken into account in the computational to obtain the coefficient power for each variation. The results revealed that the turbine with an angle of attack of 5°and TSR value of 5.0 has higher power coefficient value by 0.469 as compared with its angle of attack of 10°. It should be noted here that the increase of the angle of attack up to 10° resulted in a significant reduction of the power coefficient value of 0.206 as the value of TSR about 4.28. The addition of the Savonius Rotor results in increasing efficiency of the turbine for sea current applications.

Performance improvement of a new proposed Savonius hydrokinetic turbine: a numerical investigation

Computational fluid dynamic analysis was conducted with a new proposed Savonius hydrokinetic turbine with a parabolic blade shape specifically geared toward a small-scale power extraction. This parabolic blade geometry was developed by manipulating a couple of disparate kinds of blades in the recent past i.e. semicircular and arc shaped followed by a straight arc. The developed hydrokinetic turbine was tested numerically in a symmetric channel and its performance was evaluated concerning the power, thrust and torque coefficients. Simulations were also implemented with two other mentioned blades. The effects of Reynolds number at different tip speed ratios on the dynamic and static performance of all three models were discussed as well. The present investigation demonstrated a gain of 7.7% and 12% in maximum power coefficient with the new proposed Savonius hydrokinetic turbine by parabolic blade shape than that of the arc shaped followed by a straight arc and semicircular, respectively. Likewise, for this new proposed turbine, the maximum value of static torque coefficient improved by 4% and 25.8% than that of the arc shaped followed by a straight arc and semicircular, severally. For all three simulated blade profiles, the best performance was experienced at an optimum value of tip speed ratio 0.98 and Reynolds number 2 × 105. However, the new proposed turbine at all Reynolds numbers and tip speed ratios in the scope of this research showed a better performance than the other simulated models.

Development of a Linear Acoustic Array for Aero-Acoustic Quantification of Camber-Bladed Vertical Axis Wind Turbine.

Vertical axis wind turbines (VAWT) are a source of renewable energy and are used for both industrial and domestic purposes. The study of noise characteristics of a VAWT is an important performance parameter for the turbine. This study focuses on the development of a linear microphone array and measuring acoustic signals on a cambered five-bladed 45 W VAWT in an anechoic chamber at different tip speed ratios. The sound pressure level spectrum of VAWT shows that tonal noises such as blade passing frequencies dominate at lower frequencies whereas broadband noise corresponds to all audible ranges of frequencies. This study shows that the major portion of noise from the source is dominated by aerodynamic noises generated due to vortex generation and trailing edge serrations. The research also predicts that dynamic stall is evident in the lower Tip speed ratio (TSR) region making smaller TSR values unsuitable for a quiet VAWT. This paper compares the results of linear aeroacoustic array with a 128-MEMS acoustic camera with higher resolution. The study depicts a 3 dB margin between two systems at lower TSR values. The research approves the usage of the 8 mic linear array for small radius rotary machinery considering the results comparison with a NORSONIC camera and its resolution. These observations serve as a basis for noise reduction and blade optimization techniques.

On the Performance of Small-Scale Horizontal Axis Tidal Current Turbines. Part 1: One Single Turbine

The blade number of a current tidal turbine is one of the essential parameters to increase the stability, performance and efficiency for converting tidal current energy into rotational energy to generate electricity. This research attempts to investigate the effect of blade number on the performance of a small-scale horizontal tidal current turbine in the case of torque, thrust coefficient and power coefficient. Towards this end and according to the blade element momentum theory, three different turbines, i.e., two, three and four-bladed, were modeled using Solidworks software based on S-814 airfoil and then exported to the ANSYS-FLUENT for computational flow dynamics (CFD) analysis. SST-K-ω turbulence model was used to predict the turbulence behavior and several simulations were conducted at 2 ≤ tip speed ratio ≤ 7. Pressure contours, turbulence kinetic energy contours, cut-in-speed-curves, and streamlines around the blades and rotors were extracted and compared to provide an ability for a deep discussion on the turbine performance. The results show that in the case of obtainable power, the optimal value of tip speed ratio is around 5, so that the maximum power was achieved for the four-bladed turbine. Out of optimal condition, higher blade number and lower blade number turbines should be used at less than and greater than the optimal values of tip speed ratio, respectively. The results of simulations for the three-bladed turbine were validated against the experimental data with good agreement.

Comparative Numerical Analysis on Vertical Wind Turbine Rotor Pattern of Bach and Benesh Type

In this work, 3D models in classic configuration of Bach and Benesh rotor type, as well as models with modified blade pattern geometry were analyzed from the air circulation point of view inside the rotor enclosure in order to identify the operating parameters differences according to rotor geometric modified configuration. Constructive design aspects are presented, as well as results obtained from the virtual model analysis in terms of circulation velocity and pressure values which enhance rotor operation related to torque and power coefficients. The rotors design pattern is made according to previous results obtained by different researchers who have performed numerical analysis on virtual models and tests on the experimental rotor models using the wind tunnel. The constructive solutions are describing two-bladed rotor models, in four new designed constructive variants and analyzed using ANSYS CFX. The air velocity specific values, static and total pressure recorded at the rotor blade level are highlighted, that influence the obtaining of rotor shaft torque and power. Also torque coefficient (CT) and power coefficient (CP) values according with specific values of tip speed ratio (TSR) are presented for each analyzed case. The analysis results show higher power coefficient values for analyzed Bach V2 and Benesh V2 rotor modified models compared to the classic Bach and Benesh models for 0.3 TSR of 0.11–012 CP, 0.4 TSR of 0.18 CP (Benesh V2 model) and 0.27 CP at 0.6 TSR (Bach V2). The resulted values confirm that Benesh V2 model offers higher CP up to 5% at TSR 0.3, 2% at TSR 0.6 and 3% at TSR 0.4 compared to the Benesh classical model. The Bach V2 model offers 4% higher CP compared to the classic Bach model at TSR 0.6. Based on these results it is intended the further analytical and experimental research in order to obtain optimal rotor pattern.

Performance of Double Blade Savonius Rotor at Low Rotational Speed

The performance of the single and double blade Savonius rotors are numerically analyzed using the K-ε/realizable turbulence model. The computations are implemented at different values of tipspeed ratio from 0.2 to 0.4 with a step of 0.05. Both rotors have the same dimensions with an external overlap between their blades equals 0.02 m. The results indicate that the double blade rotor performs better than the single blade rotor in terms of power coefficient. In addition, the torque coefficient is improved at all tested values of tip-speed ratio. Furthermore, the results of the simulation show that the maximum power coefficient was 0.163 at tip-speed ratio = 0.4 for the double blade rotor, whereas the maximum improvement of the double blade rotor occurs at tipspeed ratio = 0.2 with a percentage of 11.86% compared to the single blade rotor. Moreover, the highest value of the torque coefficient was 0.524 at tip-speed ratio = 0.2 for the double blade rotor.

Electronic control for optimizing power absorption of darrieus vertical axis wind turbine by adjusting angle of attack method

This paper presents a mechanical design and electronic control for the angle of attack on the Vertical Axis Wind Turbine (VAWT) darrieus type with NACA0015 and 3 blades. This research was conducted to obtain high-efficiency absorption power on various wind speeds. The VAWT mechanical design is based on systematic calculations with a height of 150cm and a diameter of 120cm. NACA0015 airfoil with calculations in the NACA airfoil database obtained blade length of 15.892cm and width of 1.905cm. The electronic control on this system, Arduino mega controller, has input from an anemometer sensor, and rotary encoder sensor. While, the output is servo motors for 3 blade. A microprocessor control unit is programmed to control the adjustment of blade angle of attack. The angle of attack is defined by wind speed, angular speed of VAWT, and a defined TSR (Tip Speed Ratio). The angle of attack control method is PID (Proportional-Integral-Derivative) algorithm. By setting the TSR value constantly at 3-4, the angle of attack will be adapted even on any various wind speed. Expected result, the maximum power absorption will be obtained on various wind speed. This system can increase power efficiency of VAWT up to 35-40%.

A Dynamic Rotor Vertical-Axis Wind Turbine with a Blade Transitioning Capability

This work presents an optimized design of a dynamic rotor vertical-axis wind turbine (DR VAWT) which maximizes the operational tip-speed ratio (TSR) range and the average power coefficient (Cp) value while maintaining a low cut-in wind velocity. The DR VAWT is capable of mimicking a Savonius rotor during the start-up phase and transitioning into a Darrieus one with increasing rotor radius at higher TSRs. The design exploits the fact that with increasing rotor radius, the TSR value increases, where the peak power coefficient is attained. A 2.5D improved delayed detached eddy simulation (IDDES) approach was adopted in order to optimize the dynamic rotor design, where results showed that the generated blades’ trajectories can be readily replicated by simple mechanisms in reality. A thorough sensitivity analysis was conducted on the generated optimized blades’ trajectories, where results showed that they were insensitive to values of the Reynolds number. The performance of the DR VAWT turbine with its blades following different trajectories was contrasted with the optimized turbine, where the influence of the blade pitch angle was highlighted. Moreover, a cross comparison between the performance of the proposed design and that of the hybrid Savonius–Darrieus one found in the literature was carefully made. Finally, the effect of airfoil thickness on the performance of the optimized DR VAWT was thoroughly analyzed.