Tip Speed Ratio Research Articles

A Novel Wind Energy Gathering Structure for the Savonius Wind Turbine and Its Parameter Optimization Based on Taguchi’s Method

An auxiliary structure can significantly improve the wind-trapping capacity of the Savonius wind turbine. In this study, a novel auxiliary structure called a wind energy gathering structure (WEGS) is proposed, and its five parameters, namely the lengths of the shrinkage and diffusion tubes, the length of the centerboard, the length of the throat, the length of the wind board, and the shrinkage and diffusion angles, are investigated using computational fluid dynamics (CFD) and Taguchi’s method. Meanwhile, Taguchi’s method and ANOVA reveal that among the studied parameters, the shrinkage and diffusion angles, the length of the centerboard, and the lengths of the shrinkage and diffusion tubes have a more significant influence on the performance of the WEGS. At a tip speed ratio (TSR) value of 1 and a wind speed of 7 m/s, the optimized combination of the WEGS parameters obtained by Taguchi’s method improves the mean torque coefficient of the turbine by 42.1%. Moreover, at other TSRs (0.6–1.2), the turbine with the WEGS also outperforms an open turbine in terms of aerodynamic (increases of 20.1–53%) and lifetime performance.

Optimization of slot parameters for performance enhancement of slotted Savonius hydrokinetic turbine using Taguchi analysis

Hydrokinetic technology is an innovative approach to generate sustainable energy from river systems by using the kinetic energy of free-flowing water. To utilize such energy hydrokinetic turbines are being employed to harness the kinetic energy from flowing water. In this paper, a CFD study has been carried out to improve the efficiency of the Savonius turbine with the application of proposed slotted blades and validated with the experimental study. Also, this study aims for the optimization of a slotted blade Savonius hydrokinetic turbine (SHT) performance by examining different design parameters and their relationship using the Taguchi method. This study reveals that slot gap (y) has the greatest influence on turbine performance, followed by slot shape factor (ε), slot position (f), and tip speed ratio (λ). Moreover, the optimal combination of four parameters for maximising the efficiency of the slotted SHT is y = 1.5 mm, ε = 0.6, f = 1 % of blade diameter, and λ = 0.7 based on signal-to-noise (S/N) ratio. At this optimum combination of slotted blade profile, performance of slotted blade SHT increases by 45.19 % compared to conventional SHT. There is a slight difference of 4.16 % between experimental and computational results obtained for optimum Taguchi design.

High-Precision Numerical Investigation of a VAWT Starting Process

For both conventional and renewable energy conversion processes, computational fluid dynamics (CFD) has been used to address more energy-related challenges in recent decades. Using CFD to investigate vertical-axis wind turbines has become more common in recent years. The main goals of this application have been to more accurately predict the turbine’s performance and to comprehend the complicated nature of the complex turbulent flow. The vertical-axis wind turbine (VAWT) simulation for energy-generating applications has several intricate components. One of them is the study of the chaotic flow that occurs during the first stages of the starting process, and which greatly influences overall effectiveness. In this article, the performance of the wind turbine was increased using a passive flow control approach. The numerical research was carried out using Large Eddy Simulation for four alternative tip speed ratios in both cases, the classic and the optimized case, equipped with a vortex trap on the extrados of the blades. The power and torque coefficient variations, as well as the velocity magnitude contours, show that the starting process may begin with a significant improvement in efficiency when flow control is used.

Experimental Optimization of the SG6043 Airfoil for Horizontal Axis Wind Turbines Using Schmitz Equations

This study presents the experimental optimization of the SG6043 airfoil for horizontal axis wind turbines (HAWTs) using the Schmitz equation, focusing on enhancing power output and elucidating the surface flow structure. Two blade models, M1 (conventional) and M2 (optimized), were designed and tested at rotational speeds of 400 rpm and 600 rpm across a range of tip speed ratios (TSR). The M2 model, optimized using Schmitz equations, demonstrated significantly improved performance compared to the M1 model at both rotational speeds. At 400 rpm, the maximum power coefficient (CP) for M1 was 0.274, while M2 reached 0.419, indicating a 52.91% improvement. At 600 rpm, M1 achieved a maximum CP of 0.293, whereas M2 attained 0.458, representing a 56.31% enhancement. The M2 model also showed superior performance at higher TSRs, with the highest percentage increase in CP recorded at 4.9 TSR, reaching 574.54%. Additionally, dynamic surface oil-flow visualization experiments were conducted to examine flow behavior on the blade surfaces. Results indicated better flow attachment in the M2 blade due to its optimized twist angle and chord length, particularly in the mid-section, leading to delayed flow separation. The reattachment observed on the suction side of the M2 model, following the laminar separation bubble (LSB), which was absent in the M1, contributed to its higher aerodynamic efficiency and overall power performance. These findings confirm that the optimized SG6043 airfoil design, guided by Schmitz equations, offers significant improvements in HAWT performance, particularly under varying operational conditions.

Optimization of the power performance for three hybrid Darrieus-Savonius rotors based on the Taguchi method

Abstract The hybrid vertical-axis wind turbine is a unique design that overcomes the efficiency limitations of Savonius rotors and the start-up challenges of Darrieus rotors. This study uses the Taguchi optimization method to enhance the performance of a cluster of three hybrid Darrieus-Savonius vertical-axis wind turbines. The optimized parameters include distances between adjacent turbine centers, configuration angles, rotational directions, and the pitch angle. The study is the first to investigate the effect of varying the pitch angle of Darrieus airfoil blades on hybrid design performance. The optimal configuration of the three hybrid VAWTs and the isolated rotor is analyzed through flow velocity, pressure, and turbulence kinetic energy contours. The results show that the pitch angles have the greatest effect on the rated power coefficient among other studied influencing parameters. The optimal cluster configuration’s performance improvement is due to the favorable velocity gradient around the blades. Compared to the isolated rotor, the power coefficient enhancement for the optimal case is 46.545% at the rated tip speed ratio of 3.08. The hybrid rotor in the cluster can achieve almost the same power as the isolated rotor up to a tip speed ratio of 4.1 instead of 2.86 for the isolated rotor. However, the decrease in overall efficiency for some cluster configurations is due to wake flow intensity and trapping between the rotors, which causes a stagnation zone.

Aerodynamic characteristics of tall building with wind turbines at corners

This study experimentally investigates the impact of a pair of vertical-axis wind turbines at the leading corners of a tall building on its aerodynamic characteristics. These wind turbines have the potential to serve dual purposes: harnessing wind energy under normal wind conditions and mitigating wind loading of the building under strong wind conditions. The wind tunnel testing results in this study indicate when the tip speed ratio of the turbines is 0.34, with the wind turbines rotating toward downstream, the standard deviation of lift coefficient of the building decreases by 30.9%. Meanwhile, the mean pressure coefficient and the standard deviation of pressure coefficient on both the side face and leeward face of the building also exhibit a certain degree of reduction. The peak value of the power spectral density of lift coefficient of the building is also significantly decreased. This study clearly demonstrates that the wind turbines at the leading corners of tall buildings have the potential to effectively reduce wind loading of the buildings.

Comprehensive study of vortices interaction and blades height effect in a Darrieus vertical axis wind turbine with J‐type blades

AbstractThere is a growing demand to improve the performance of vertical axis wind turbines to facilitate their commercialization for application in urban areas. This study utilizes a 3D numerical analysis to examine the influence of different vortices generated on turbine efficiency with straight and J‐type blades. The numerical simulation of this study employs the Reynolds‐Averaged Navier–Stokes equations and ‎sliding ‎mesh techniques ‎to more accurately model the rotational motion of blades about the turbine axis in relation to the ‎wind. Comparing the output ‎torque and the flow field at different span‐wise sections, the J‐type blades achieve better ‎performance at mid‐spans where the effect of stall vortices is dominant. Conversely, the lower ‎performance of J‐type blades is seen at tip spans due to stronger tip vortices. Investigations also ‎reveal the criticality of the downwind region on the overall performance at high tip speed ratios. It is observed that by ‎increasing the height, the tip vortices are limited to the tip sections, and stall vortices expand further ‎along the blade. At TSR = 1, the improvement by J‐type blades rises from 10% at a height of 0.8 m to 44% ‎at 3 m. The growth in height at lower wind speeds becomes more beneficial. Compared to the straight blades, the self‐starting ‎generated torque by J‐type blades for heights of 0.8, 1.2, and 1.6 m, are improved by 15.6%, ‎‎26.9%, and 34.7%, respectively. Overall, it is concluded that by increasing the blade height, the superiority ‎of the J‐type blade becomes more noticeable as the blade mainly contributes to suppressing the stall ‎vortices effect where the tip vortices effect is not presented. ‎

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.

Experimental study on enhancing the performance of hydrokinetic integrated Darrieus-Savonius rotor in open water-channel

The kinetic energy stored in water streams could be used to generate electricity via hydrokinetic rotors, due to the availability of kinetic energy from flowing water. Darrieus and Savonius are vertical axis kinetic rotors, they are promising for generating power in low speed flows. The integrated Darrieus- Savonius hydrokinetic rotor works on the principles of integrated forces including lift and drag forces. An experimental investigation has been conducted to get the optimum configuration for Darrieus-Savonius integrated rotor in order to attain improved self-starting and high-power-factor in open channel water flow, under different inflow conditions. This study investigated the effects of the radius ratio, add-on angle, water heights, and flow velocity on performance of hydrokinetic integrated Darrieus-Savonius rotor with three standard NACA 020 airfoil shape as Darrieus rotor and single/double stage semi-circular blades as Savonius rotor on the power factor. Three radius ratios (R.R) namely (0.8, 0.6 and 0.4) and add-on angles of (0o, 30o, 45o, 60o and 90o) were studied. The experimental channel was (26 m) long water flume with a (1m wide ×1.2 m depth). The horizontal walls of the flume were made of glass with a strengthened frame, to permit visual examination. The flume entrance consisted of a receiving tank (3 m long, 1.5 m wide, and 0.75 m depth), a honeycomb pattern pipe box, and a screen box field with a large stone to dissipate the water turbulence and energy at the entrance. Two centrifugal pumps were used to supply water to the channel. Darrieus-Savonius integrated rotor was placed at distance equal to ten times width of the experimental channel, to avoid any turbulence and to make sure that the flow was steady.Based on the experimental results, it was observed that the optimum Cp values at λ (1.84), add-on angle of (45o) and R.R (0.4, 0.6 and 0.8) were (0.335, 0.29 and 0.299) respectively. The maximum hybrid performance was attained at R.R (0.4), add-on angle (45o) and tip-speed ratio (1.8) and Re (240x106) with value of (0.339). Decrease in the Re values by 25 % enhanced the performance by 1.19 %. Accordingly, it is not necessary to rely on Re values in calculating the power-factor values compared to the influence of the rest of the variables.

Numerical investigation of turbulent flow over a small-scale vertical axis wind turbine

The present paper aims to analyse the aerodynamics of turbulent fluid flow over a vertical axis wind turbine (VAWT). A 2D study is carried out for a two-bladed SAVONIUS wind turbine, where the rotor diameter is D=20cm. The governing equations (Unsteady Reynolds Averaged Navier Stokes URANS) are solved numerically using a CFD (computational fluid dynamics) open-source code based on the finite volume method; the SST turbulence model is applied for the system closure. An arbitrary mesh interface (AMI) technique is applied at the sliding interface boundary, which is a circular surface separating between the rotating zone and the fixed zone where the mesh remains stationary. The numerical results allow predicting the vorticity and pressure distributions over a rotating wind turbine for different tip speed ratios in order to characterize the generated wake. The velocity deficit is calculated for different positions behind the rotor to characterize the disturbance rate of the flow.

Study on aerodynamic and coupled motion response characteristics of floating vertical axis wind turbine

ABSTRACT To improve the efficiency of a floating VAWT (FVAWT), the aerodynamic and coupled motion response characteristics of 5MW Φ-type FVAWT are studied in fully coupled system. Based on the computational fluid dynamics (CFD) method, the dynamic fluid body interaction (DFBI), overlapping grid and dynamic mesh technique are adopted for numerical simulations. Under wind-wave coupling conditions, the power coefficient (Cp) and motion response of FVAWTs with different tip speed ratios (TSR) and height-todiameter ratios (η) are analysed. The mechanism of platform heave motion on torque Q generation of VAWT is explored. The results show that the FVAWT with height-to-diameter ratio of 1.2 and tip speed ratio of 5 has optimal aerodynamic and motion performance. Under the optimal tip speed ratio, the Cp of the offshore FVAWT is 5.21% higher than that of the land VAWT. As the floating platform rises, the torque of wind turbine decreased correspondingly, and vice versa.

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.

Optimizing a vertical axis wind turbine with helical blades: Application of 3D CFD and Taguchi method

Vertical axis wind turbines (VAWT) with helical blades are being interested in urban areas due to the low dependency on the wind direction and also due to low noise production. In spite of good self-starting and smooth operation as the advantages of this type of turbine, its optimizing has not been reported in literature yet and is the subject of this research. A primary investigation by 3D computational fluid dynamics (CFD) to simulate the air flow about the above type of VAWT in the first step showed the importance of three design variables of tip speed ratio, helical angle, and airfoil chord length. However, in the second step, CFD runs were very time consuming and costly. For considering five values for each design variable, 53=125 cases had to be simulated by 3D CFD. Thus, by the use of Taguchi method and with definition of an orthogonal array named L-25, the number of required 3D CFD simulations reduced from 125 to 25. Then, the optimum values of variables were obtained as 1.33 for the tip speed ratio, 30 degrees for the helical angle, and 0.4 m for the airfoil chord length. At the optimum point, the average power coefficient increased to 0.17542. The presented research is novel for optimizing VAWT with helical blades.

Experimental and numerical investigation of Zephyr-type wind turbine

The search for more environmentally friendly energy sources has been prompted by growing environmental concerns. In this regard, wind energy can be an alternative viable source of energy for world electricity demand supply. Despite of their benefits in terms of simplicity of manufacture, independency on wind direction and good starting ability in turbulent flow, Savonius wind turbines as a vertical axis wind energy converter are not recommended for large-scale power generation because of their poor performances. This research emphasizes on the performance improvement of a Zephyr wind rotor (ZWR). Experimental tests were conducted in a wind tunnel for different Reynolds numbers. Maximum power coefficient of 0.074 was recorded for Re = 158,000 corresponding to V∞ = 10 m s−1 at a tip speed ratio of λ = 0.99. Numerical study was carried out with the use of Ansys Fluent 17.0 software through transient 3D simulations investigating the optimization of the ZWR rotor blades and stator vanes with the aim of performance betterment. Maximum power coefficient of 0.168 was found with 8-bladed ZWR with 12 stator vanes. Aerodynamic properties were also improved.

Evaluation of maximum power point tracking methods for a marine current energy converter

AbstractMarine current power is attracting more attention as a renewable energy option. Similar to wind power, marine current power often requires a maximum power point tracking (MPPT) method to optimize power extraction from the free‐flowing water. Research into MPPT methods for marine current power remains limited. Therefore, this paper presents a comprehensive investigation of MPPT methods for marine current power, building upon similar research in wind power. Three methods, namely the optimal tip speed ratio (OTSR), optimal torque (OT), and two variants of the perturb and observe (P&amp;O) method, are explored. Using a simulation model developed for a specific marine current energy converter, where hydrodynamic calculations are coupled with electrical simulations, the study demonstrates that the OTSR method achieves MPPT with a comparably fast convergence time. After a change in water speed, the OTSR method achieves optimal operation within two turbine rotations. Additionally, the P&amp;O methods are shown to achieve MPPT, albeit with a significantly longer convergence time. However, the P&amp;O methods can be more convenient since no model of the system is required, and no water speed measurements are necessary. The proposed implementation of the OT method underperforms but positions the system close to the optimal operational point.

Power performance enhancement for a three-turbine cluster of two-stage Savonius rotors using Taguchi approach

Choosing an optimal Savonius vertical-axis wind turbine (VAWT) arrangement that delivers the largest power coefficient is a significant challenge. So, in this paper, an optimization of the power performance using the Taguchi technique is presented for a three-turbine cluster of two-stage Savonius rotors. A three-dimensional, unsteady, incompressible airflow model is numerically solved using ANSYS and validated using published experimental and numerical studies. The power performance of the three VAWTs is optimized by adjusting five factors, including the relative angles between the turbines (ϕ12 and ϕ13), the rotation directions (RD), and the turbine spacings (S12 and S13). The rated power coefficient (CP) and its corresponding Tip Speed Ratio (TSR) are numerically obtained for an L16 (45) orthogonal array (OA). After the signal-to-noise ratio analysis, the optimal case is obtained. Results indicate that the configuration angles have the main effect on CP, the turbine spacing between the first and second rotors and the combination of rotation directions have the lowest effect. The optimal case is found to be (S12 = 2D, S13 = 2.4D, ϕ12 = ϕ13 = 70⁰, and RD = -, +, -), resulting in an increase of 19.69 % in CP compared to the isolated turbine at a rated TSR of 0.8.

Performance and mechanism of adaptive pitch control in a floating vertical axis wind turbine with a surge motion

Floating vertical axis wind turbines are bearing complex aerodynamic fatigue loads due to the movement of the platform and the reciprocating variations in the angle of attack and the blade relative wind speed. To explore the effect of the surge motion of the platform and verify the performance and acting mechanism of adaptive pitch control on reducing the fatigue loads and improving the power coefficient, a floating vertical axis wind turbine with three motion forms (non-surge, pure surge, and surge-adaptive pitch) is investigated in the condition of a low tip speed ratio with a high incoming wind speed. The results show that the surge motion enhances the fatigue loads, with the power coefficient less affected. The adaptive pitch control reduces the enhanced fatigue loads and improves the power coefficient by nearly twice. Vorticity and pressure distributions verify that the fluctuation ranges of the angle of attack and the blade relative wind speed are expanded by the surge motion, and the angle of attack is reduced by the adaptive pitch control especially in the upwind section, with the flow separation mitigated. However, the effects of the surge motion and the pitch variation are also influenced by the shedding vortex and the flow separation reattachment. For the upwind part of the blade aerodynamic forces, with the surge amplitude increase or the surge period decrease, the global amplitudes are increased gradually by the surge motion and then reduced by the pitch control, with the load reduction performance enhanced gradually.

Drag reduction of lift-type Vertical axis wind turbine with slit modified Gurney flap

This study examines aerodynamic performance enhancement of Vertical Axis Wind Turbine (VAWT) blades with Gurney flap (GF) modified by slits. A quasi-3D computational fluid dynamics solution based on Reynolds-averaged Navier-Stokes model is employed to evaluate the effectiveness of slit GF blades, in particular the lift-to-drag ratio. The computational domain includes three pairs of GFs and slits combination along the blade span-wise direction to allow quasi-3D flow development while applying translational periodic boundary condition on the two end-wall boundaries. The inlet velocity is 9 m/s for a VAWT configuration with Tip Speed Ratios (TSRs) of 1.44, 2.64, and 3.3, respectively and each of these TSRs represents low, medium, and high regimes of TSRs. Simulation results have shown a significant 8% drag reduction for blades with slit GFs at medium range of TSRs, albeit with a 2% decrease in lift compared to blades with clean GFs. This improves the lift-to-drag ratio and enhances moment production. The power generation also shows increases of 1.5%, 6.5%, and 11.3% at low, medium, and high TSR regimes, respectively, for the analysed slit GF blades. The drag reduction is primarily attributed to the generation of small-scale vortices by the slit, dissipating large coherent flow structures more rapidly in the near wake-field.

Design of a recirculating water channel for the development of a hydrokinetic turbine

This study presents the design, construction, and operational details of an experimental recirculating water channel dedicated to the assessment of hydrokinetic turbines, including a propeller-type turbine and a H-Darrieus turbine, since it offers a controlled testing environment. The recirculating water channel had overall dimensions of 5 m in length, 0.35 m in width, and 0.5 m in depth, it allows for the replication of various water flow conditions and permits a maximum achievable flow velocity of 0.6 m/s, which closely resembles real-world scenarios. Afterwards, a propeller- type turbine and a H-Darrieus turbine underwent characterization within the channel, and a performance curve constructed through the coefficient versus the blade tip speed ratio (TSR) revealed a peak efficiency of 0.2129 at a TSR of 2.952 for the propeller turbine, and a higher peak efficiency of 0.3076 at a TSR of 0.38 for the H-Darrieus turbine. The versatility of this experimental setup makes it a valuable platform for in-depth performance studies of hydrokinetic turbines. This water channel and its systematic characterization process represent a vital resource for conducting efficiency and behavior analyses across a wide range of operational parameters related to hydrokinetic turbine technologies.

Enhanced Analysis of Ice Accretion on Rotating Blades of Horizontal-Axis Wind Turbines Using Advanced 3D Scanning Technology

This study investigated the meteorological conditions leading to ice formation on wind turbines in a coastal mountainous area. An enhanced ice formation similarity criterion was developed for the experimental design, utilizing a scaled-down model of a 1.5 MW horizontal-axis wind turbine in icing wind tunnel tests. Three-dimensional ice shapes on the rotating blades were obtained and scanned using advanced 3D laser measurement technology. Post-processing of the scanned data facilitated the construction of solid models of the ice-covered blades. This study analyzed the maximum ice thickness, ice-covered area, and dimensionless parameters such as the maximum dimensionless ice thickness and dimensionless ice-covered area along the blade. Under the experimental conditions, the maximum ice thickness reached 0.5102 m, and the ice-covered area extended up to 0.5549 m2. The dimensionless maximum ice thickness and dimensionless ice-covered area consistently increased along the blade direction. Our analysis of 3D ice shape characteristics and the ice volume under different test conditions demonstrated that wind speed and the liquid water content (LWC) are critical factors affecting ice formation on blade surfaces. For a constant tip speed ratio, higher wind speeds and a greater LWC resulted in increased ice volumes on the blade surfaces. Specifically, increasing the wind speed can augment the ice volume by up to 57.2%, while increasing the LWC can enhance the ice volume by up to 149.2% under the experimental conditions selected in this study.