Increase In Power Coefficient Research Articles

Numerical assessment of ice formation processes and its impact on a variable-pitch unmanned aerial vehicles propeller in forward flight

Unmanned aerial vehicles (UAVs) encounter significant challenges in freezing climates, as atmospheric ice accretion adversely impacts both flight safety and aerodynamic performance. This study provides an in-depth numerical investigation into the ice accretion process and its implications on the aerodynamic performance of UAV propeller. The analysis explores at various propeller blade pitching angles and rotational speeds. Detailed flow field analysis around propeller blade surfaces is conducted to address the performance degradations associated with ice accretion. The investigation reveals a noteworthy shift in ice shapes and extents with varying pitching angles and rotational speeds. The iced propeller demonstrates increased aerodynamic losses, marked by large size separation bubbles aft the ice shapes at outer radial locations. Remarkably, at higher pitching angles, the iced propeller outperforms the baseline propeller, followed by a propeller with increased rotating speed. For both baseline and higher pitching angles, the most significant losses in thrust coefficient 57.60% and 25.39%, respectively, occur at −2 °C, accompanied by maximum spikes in power coefficient of 140.08% and 93.92% at −4 °C. Meanwhile, an increase in rotating speed results in a decrease in thrust coefficient by 48.60% and an increase in power coefficient by 150.66% at an icing temperature of −4 °C.

Effects of the morphed trailing-edge flap parameters on the aerodynamic performance of NREL Phase II wind turbine

This study assesses the impact of three morphed trailing-edge flap (MTEF) parameters (flap deflection angle β, flap length b, and flap span length l) on increasing power and axial thrust coefficients and their comprehensive effect on wind turbines using computational fluid dynamics (CFD) method. The detailed analysis is performed on seven morphed blades at eight different wind velocities. The obtained results show that β results in the largest unit power coefficient increase rate and unit axial thrust coefficient increase rate, while l results in the smallest ones. In addition, b results in the largest power-thrust ratio increase rate. The optimum blade is achieved for β = 3°, b/ c = 0.3, and l/ R = 0.3, which results in additional power increase of 15.24% and axial thrust increase of 9.53% at a tip speed ratio of 5.949, compared with the original wind turbine.

ADVANCED TURBINE WORKING: IMPACT OF WINGLET ON VERTICAL WIND TURBINE DARRIEUS TIPE H

In this study, the effect of winglets on improving the performance of type h darrieus wind turbines was investigated. The aim is to determine the most suitable winglet design and find out the magnitude of the increase in wind turbine performance. The method used is experimentation to find the RPM and torque used for calculate the TSR value and turbine power. From all the trial and error experiments, the type of blended winglet that best suited the characteristics of the VAWT. The experimental results show that the addition of blended winglet increases RPM of 13.6% in the 3-blade turbine and turbine it increases of 9% in the 4-blade turbine. The increase in average torque is 13.2% in a 3-blade turbine and 9.4% in a 4-blade turbine. The average increase in power coefficient is 11% in a 3-blade turbine and 9% in a 4-blade blade. In conclusion, the addition of blended winglets produces better torque and power compared to turbine models without winglets.

Modeling and performance analysis of resonant self-biased magnetoelectric transducers

Compared with single-phase multiferroic materials, magnetoelectric (ME) composites composed of piezoelectric and magnetostrictive materials have great ME coupling, and have received widespread attention in various application fields. The application of ME devices in wireless power transfer (WPT) is attractive due to their compactness and ability to operate at lower frequencies than conventional coils. However, traditional ME composites rely on permanent magnets or electromagnets to provide biased magnetic fields, thus leading to problems such as high noise, large size, and high cost, which significantly hinder the advancement of miniaturized and high-performance ME devices. To solve this problem, a self-biased ME laminated structure based on the magnetization grading effect is proposed in this work. Using the equivalent magnetization and nonlinear magnetostrictive constitutive relationship, a finite element simulation model for a self-biased ME transducer operating in L-T mode is constructed. The ME coupling performances without DC bias in bending vibration mode and stretching vibration mode are studied. Based on the model, the corresponding experimental samples are prepared for measurement. The measurement results are in agreement with the simulation data, thereby validating the accuracy and effectiveness of the model. The measured results show that the Metglas/Galfenol/PZT-5A structure can exhibit more significant self-biased ME effect under the stretching resonance mode than under bending resonance mode. Its ME coefficient attains a notable value of 10.7 V·cm<sup>–1</sup>·Oe<sup>–1</sup> at 99.4 kHz, while ME power coefficient reaches 5.01 μW·Oe<sup>–2</sup> at 97.9 kHz. Its on-load ME power coefficient can reach up to 4.62 μW·Oe<sup>–2</sup> at 99.3 kHz without impedance matching. When an external bias magnetic field of 25 Oe is applied, these performance indexes increase significantly to 47.06 V·cm<sup>–1</sup>·Oe<sup>–1</sup> at 99.4 kHz and 82.13 μW·Oe<sup>–2</sup> at 99.0 kHz, respectively. The simulation results further show that the performance of the self-biased ME transducer can be significantly improved by increasing the thickness of the high permeability layer. For example, by increasing the Metglas layer thickness from 30 μm to 90 μm, both the ME coefficient and ME power coefficient increase rapidly by 2.47 times and 6.96 times the original values, respectively. Self-biased ME transducers effectively reduce the dependence on external bias magnetic field, thereby providing a good approach for applying and developing ME composites in low-frequency WPT systems.

PENGARUH KONTROLER MAXIMUM POWER POINT TRACKING (MPPT) TERHADAP EFISIENSI DAYA VERTICAL AXIS WIND TURBINE (VAWT) TIPE SAVONIUS DUA SUDU

The purpose of this research is to determine the effect of Maximum Power Point Tracking (MPPT) controller on the power efficiency of a two-bladed Savonius vertical axis wind turbine (VAWT) with a dimensional diameter of 0.9 m and a height of 1 meter, using 1 mm thick stainless steel plate blades. The MPPT controller is applied to the two-bladed Savonius wind turbine to maintain its operation at the maximum power point. The Perturb & Observe type MPPT controller is used in the study to compare the power output of the Savonius wind turbine when the MPPT system is inactive and when it is active, with three variations of load using resistors of 470 ohm, 560 ohm, and 1000 ohm. The research is conducted by subjecting the turbine blades to three variations of wind thrust at speeds of 4.9 m/s, 5.8 m/s, and 6.4 m/s. The testing without using MPPT resulted in an average power of 0.199 Watt, while using MPPT resulted in an average power of 0.620 Watt. The research findings indicate an average power difference of 0.421 Watt, representing an increase of 317.713%. The average power efficiency of the turbine increased by 2.331% compared to the calculated maximum power of the two-bladed Savonius wind turbine. The average power coefficient (Cp) of the two-bladed Savonius wind turbine without MPPT and with MPPT is 0.159% and 0.509%, respectively, indicating a positive effect of MPPT as it led to an average increase in power coefficient of 0.350%.

Effects of Gurney Flaps on the Performance of a Horizontal Axis Ocean Current Turbine

Gurney flaps can enhance the hydrodynamic efficiency of airfoils, and they are currently used in several applications, including racing cars and wind turbines. However, there is a lack of studies in the literature on the application of Gurney flaps on the Horizontal Axis Ocean Current Turbine (HAOCT). The influence of Gurney flaps on the hydrodynamic efficiency of the HAOCT is evaluated through numerical analysis. The effect of the Gurney flaps on the turbine is evaluated after the validation of the utilized numerical method is completed using the wind tunnel experimental data of the two-dimensional NACA 63415 airfoil and the water tunnel experimental data of the NACA 638xx series rotor on the clean blade. By calculating the velocity and pressure fields of the 2D airfoil by CFD, it was possible to analyze the lift improvement with the addition of the Gurney flaps by evaluating the pressure difference between the pressure surface and the negative pressure surface, and the drag improvement was due to the Gurney flaps obstructing the chordal flow of the fluid in the wake. For the 2D NACA-63415 airfoil, the drag coefficient increases with the increase in the head angle, while the lift coefficient increases and then decreases. The flap height divided by the local chord length of the Gurney flaps is 0.01, and the lift-to-drag ratio is the highest when the head angle is 4°. For the NACA-638xx turbine, the addition of Gurney flaps significantly increases the axial thrust coefficient. At lower tip speed ratios, the effect of the Gurney flaps on the rotor’s power coefficient is limited, with the greatest increase in the power coefficient at a tip speed ratio of 6 and a decrease in the power coefficient increase as the tip speed ratio increases. Increasing the height of the Gurney flaps can increase the peak power coefficient, but the power performance decreases at high tip speed ratios. The Gurney flaps distributed at the root of the rotor have less effect on the power performance. A 0.4 local radius spread of the Gurney flaps increases the peak turbine power coefficient by only 0.34%, while full-length Gurney flaps can increase the peaked blade power coefficient by 10.68%, indicating that Gurney flaps can be used to design a new HAOCT.

An investigation into the self-starting of darrieus-savonius hybrid wind turbine and performance enhancement through innovative deflectors: A CFD approach

Amidst vertical axis wind turbines, Darrieus turbines stand out for their impressive efficiency. However, these turbines encounter a significant challenge regarding their self-starting ability. Therefore, the current study seeks to explore the effects of combining Savonius and Darrieus turbines on the self-starting capability of the Darrieus turbine and propose a new wind turbine design with superior starting torque. Additionally, the study investigates the effectiveness of novel deflectors placed in front of and alongside the hybrid turbine, focusing on increasing the efficiency of the hybrid turbine. For this purpose, numerical simulations are carried out using a two-dimensional computational fluid dynamics (CFD) approach to simulate the flow field. The SST k-ω turbulence model is employed to provide closure for the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. Also, the modeling validation and verification were performed by sensitivity analysis of mesh distribution and time step. The research findings indicated that coupling the Darrieus and Savonius turbines improved the hybrid turbine's self-starting ability, with a 26.91% increase in power coefficient (Cp) at the lowest tip speed ratio (TSR) of 1.45. However, as TSR increases, the hybrid turbine's performance decreases due to the Savonius turbine's limited aerodynamic performance at high TSRs. This issue is solved using front and side deflectors, improving the hybrid turbine's efficiency at the optimum TSR of 2.6 by 30% and 26%, respectively, through increasing wind energy density at the upwind and leeward regions of the turbine. Furthermore, using both deflectors together, known as the double deflector configuration, has shown the best performance at both the lowest and optimum TSR.

Aerodynamic analysis of a novel pitch control strategy and parameter combination for vertical axis wind turbines

The performance of a vertical axis wind turbine (VAWT) deteriorates at low tip speed ratios (TSR) and it is mainly characterized by flow separation and dynamic stall. Several mitigating techniques have been developed recently based on flow separation and dynamic stall research activities. One of such techniques is the use of blade pitch angle control, which shows very promising optimal performance in VAWTs. However, its adaptation for periodic variation of the angle of attack remains an important issue that needs to be addressed urgently. Therefore, this paper proposes a novel pitch control strategy based on the VAWT-shape pitch motion to achieve blade dynamic pitch with the rotational parameters (TSR and azimuth angle). The pitch scale factor (μ) is introduced to proportionally vary the angle of attack. High accuracy computational fluid dynamics (CFD) methods are used to simulate dynamic changes in pitch angle, flow field and vortex shedding vorticity, with the turbulence modelled using the SST k-ω model. The results show that a 146% increase in power coefficient can be achieved using a μ of 0.3 at TSR of 1.25. Additionally, the use of dual pitch scale factors (dpsf) in the windward and leeward regions causes intense transient torque fluctuations at 0° (360°) and 180° azimuths due to a breaking distance in pitch angular velocity at these azimuths. Adding a weight function into the fitting process of the dpsf pitch curve effectively minimize these fluctuations.

Investigation of Performance Enhancements of Savonius Wind Turbines through Additional Designs

This study examines the literature on improving the low performance of Savonius wind turbines, which are a type of vertical axis wind turbine. The literature studies on improving the performance of Savonius turbines have been summarized into two categories: interior structural design and exterior additional design. Due to the extensive nature of studies focusing on interior design changes, this research primarily focuses on performance studies related to exterior design modifications of Savonius wind turbines, particularly in recent years. This study aimed to provide a comprehensive examination of these performance studies and contribute to the existing literature by presenting a systematic reference on this issue. To achieve this objective, a thorough review of turbine exterior design studies has been conducted. The focus was on determining the percentage increase in power coefficient achieved by turbines with exterior design modifications compared to the classical turbine versions. Here, it has been determined that the power coefficient values of Savonius wind turbines can reach approximately 0.400 through interior design changes. However, with the implementation of additional exterior design modifications, these power coefficient values can be further increased to around 0.520. Thus, within the scope of this study, it has been determined that the turbine power coefficients show a fairly good increase with exterior design techniques compared to interior design techniques.

An experimental and analytical study of wind turbine wakes under pressure gradient

This work is dedicated to the systematic investigation of wind turbine wakes under the effect of pressure gradients. Wind tunnel experiments are carried out with a wind turbine positioned on straight ramps of increasing angle such that it experiences an approximately linear flow speed-up/slow-down from the induction region into the far wake. Fifteen ramp angles are studied: 7 favorable (FPG), 7 adverse (APG), and 1 zero pressure gradient. The wake center is shown to follow the base flow streamline originating from a virtual turbine hub height. A quasi-linear relationship between the pressure gradient and near wake length is demonstrated. Far wake characteristics, such as the recovery of the wake center velocity deficit and wake growth rate, are observed to systematically vary with the pressure gradient. The wake recovery rate increases (decreases) with the increase in the FPG (APG), and the wake growth rate shows a linear increase from most favorable to most adverse pressure gradient. The turbine power coefficient decreases significantly with increasing APG to a greater degree than the increase in power coefficient under FPG. The engineering approach of superposing the wake deficit predicted by the standard Gaussian model on the modified base flow is shown to work for very moderate pressure gradients. In light of this, a threshold in terms of flow speed-up/slow-down along the wake trajectory is established, below which the engineering approach can be reasonably employed. Finally, a physics-based model for wakes under the pressure gradient is tested. A new theoretical relation for near wake length under the pressure gradient is proposed. Using the theoretical near wake length, the pressure gradient model predicts the turbine wakes for all cases with good accuracy and shows a significant improvement from the engineering approach.

Using vortex generators for flow separation control on tidal turbine profiles and blades

Tidal energy can play an important role in the Net Zero transition. Increasing tidal turbine performance through innovation is crucial if the cost of tidal energy is to become competitive compared to other sources of energy. The present investigation is a proof-of-concept study for the application of Vortex Generators (VGs) on tidal turbines in view of increasing their performance. The more mature wind energy industry uses passive VGs either as a retrofit or in the blade design process to reduce separation at the inboard part of wind turbine blades. Tidal turbine blades also experience flow separation and here we examine whether passive vane VGs can be used to reduce or suppress that separated flow. First, a wind tunnel investigation is performed to assess the performance of VGs on a 20% thick profile from the blade. Then, the VG effect on the 2D-profile is modelled in a Reynolds Averaged Navier-Stokes in-house solver. Results show that low profile VGs, i.e. VGs shorter than the local boundary layer, can increase the performance of the blade profile and successfully reduce flow separation. The VG effect on blade performance is examined in model scale and in full-size. VGs successfully suppress separation in both cases and it is shown that full-size information should be used for the placement of VGs. A maximum power coefficient increase of 1.05% is observed at a tip speed ratio of λ=3. The present proof-of-concept study demonstrates for the first time the potential of passive VGs to be included either in the design process of a tidal turbine blade or as a retrofit solution.

Passive control of dynamic stall in a H-Darrieus Vertical Axis Wind Turbine using blade leading-edge protuberances

Dynamic stall flow conditions affect the performance of most Vertical Axis Wind Turbine (VAWT) designs; however, the associated losses are especially relevant in smaller turbines, such as those typically used in urban environment applications. The work described in this paper experimentally evaluated the effectiveness of leading-edge protuberances in controlling the aforementioned stall behavior. A numerical study was first performed to define the leading-edge geometry to be subsequently tested in the wind tunnel. A custom experimental setup was also developed for this purpose. The wind tunnel measurements of the modified turbine showed significant performance gains over the baseline and a considerably improved self-starting behavior. The power coefficient increase was between 46% and 20% for wind velocities ranging from 5.5 m/s to 9 m/s, respectively. Nevertheless, the tip-speed ratio characteristics of the studied turbine were not meaningfully affected by the use of leading-edge protuberances.

Performance enhancement of low speed current savonius tidal turbines through adding semi-cylindrical deflectors

Qeshm channel between the Persian Gulf and Oman Sea with a maximum tidal current velocity of about 2 m/s is unsuitable for installing conventional tidal turbines. This study aims to introduce a new turbine with semi-cylinder deflectors, which is added to a Savonius tidal turbine to make feasible power extraction from this low-speed tidal current. For this purpose, Computational Fluid Dynamics analysis is done on the Savonius turbine with 2,3, and 4 blades in two cases (with and without deflectors). The results show an increase in power coefficient (CP) to 0.38 at an optimum TSR of 0.68 for two-blade Savonius Rotor by implementing semi-cylinder deflectors. In comparison, the maximum CP is 0.14 for a two-blade Savonius rotor without deflectors. Power coefficient decreases by increasing the number of blades in rotors with obstacles. CP has an upward trend by increasing the speed of water flow in the absence of deflectors. However, CP has an upward trend till 1.5 m/s current speed and after that has a downward trend in rotors with deflectors. As a general result, the Savonius turbine with semi-cylinder deflectors is very consistent with the conditions of the Qeshm channel, in which the tidal current speed is always fewer than 2 m/s.

Numerical study on the effect of out-of-phase wavy confining walls on the performance of Savonius rotor

Power generation using renewable energy, specifically from wind power is reliable, affordable and pollution-free energy. Turbine is the basic component in a wind energy conversion system. This research article, is on Savonius vertical axis wind turbine (VAWT) installed on building rooftops targeting power extraction from low wind speed. The novel idea proposed in this work is attachment of channel confinement with local waviness to increase drag on the advancing blade. The study has been carried out using ANSYS Fluent 2019 R3 software. The systematic study conducted on the effect of location of turbine in the wavy channel has been presented. The new configuration has improved the turbine output significantly. The maximum increase in power coefficient is 44.67% for waviness confinement channel than plain confinement channel.

Numerical study of the flow field around hydrokinetic turbines with winglets on the blades

Design methods and concepts that can increase the energy conversion efficiency of marine and river current turbines are of great importance for the development and wider utilization of this emerging renewable energy technology. This work is aimed to improve hydrodynamic performances of the hydrokinetic turbines to get as close as possible to the theoretical energy conversion efficiency limitation of 59.3%, known as the Lanchester–Betz–Joukowsky limit. The winglets are integrated at the turbine blade tips to reduce the effect of the tip vortex. The winglet design concept is adopted from the jet aircraft and adjusted to the hydrokinetic turbine application. The numerical investigation of the winglets impact on the hydrodynamic performances was performed using computational fluid dynamic (CFD). The results indicate that winglets subdue the strength of tip vortices, which is reflected through the increase in the power extracted. It has been confirmed that winglet height has a great influence on the power coefficient increase, which for higher winglets reaches the value above 50%. The analysis of the wake regions behind turbines pointed out that the turbines with winglets form stronger vortices in the far wake zone which may influence the back-flow turbine installed in row array.

Effect of turbulence on the performance of a pair of vertical-axis wind turbines

The focus of this study is to investigate under high turbulence intensity the performance and wake characteristics of a pair of closely spaced counter-rotating vertical axis wind turbines (VAWTs) in wind tunnel-controlled conditions. To achieve this, wind tunnel experiments for an isolated VAWT and dual VAWTs are conducted. A squared-mesh wooden grid is placed upstream of the wind turbines to increase the level of free stream turbulence. The wind tunnel tests confirm the increase in power coefficient of paired VAWTs in turbulent flows compared to smooth flows. Additionally, this study analyses the near-wake downstream of the paired turbines in both smooth and turbulent flows to better understand the flow physics.

Implementation of tubercles on Vertical Axis Wind Turbines (VAWTs): An Aerodynamic Perspective

In recent days, enhancement of Vertical Axis Wind Turbines (VAWTs) by mitigating flow deteriorating effects like dynamic stalling, unsteady wake is given great importance. The following article focuses on implementing four different tubercles on the blades’ leading edge and studying its performance and flow characteristics using CFD techniques. Results indicate that the addition of tubercles generated counter-rotating vortices and delayed flow separation and helped control dynamic stalling. Between azimuth angles 70°–160°, the flow was seen to separate only along the trough regions of the blade and remained attached along the peak regions, thus providing more torque and power. In addition to the enhancements in the flow characteristics, a 28% increase in power coefficient was observed for the optimal configuration at the optimal tip speed ratio. Additionally, a 14% increase in maximum lift generated by the blade was observed. Preliminary aeroacoustics analysis revealed a 12% and 20% decrease in the noise emissions along the blade tip and mid-plane of the turbine, respectively. Hence, it can be shown that tubercles effectively control dynamic stall, reduce noise emissions, and increase the power output of VAWTs.

A simulation investigation the performance of a small scale Elliptical Savonius wind turbine with twisting blades and sloping ends plates

Savonius wind turbine is among of simplest type of vertical axis wind turbines to produce the power from wind. Elliptical blades one of adopted geometry to design the Savonius turbine rotor. One of the most important measures to improve the performance of elliptical Savonius turbine rotor by developing the blade geometry. In this study, a CFD simulation used to investigate the effect of geometrical parameters of the small scale elliptical Savonius turbine rotor (ESTR) with inner surface wavy blades. The simulation has been implemented in a in a two configurations design models, ESTR models with twisting angle in range of (5˚ to 45˚) and ESTR models with tilt angle of end plates (3˚ to 15˚) with a constant Aspect ratio of 1 and overlap ration of 0.2. The performance evaluation were in terms of power coefficient and torque coefficient as a function of tip speed ratio. The numerical results show that an increase in the maximum power coefficient with increase of twist angle and tilt angle until optimum values of 30˚ and 12˚ for the twist angle and tilt angle, respectively. Although in all configuration show a good increase in power coefficient but there are a significant increasing in maximum power coefficient for ESTR model with twist angle of 30˚ which was 3.7% while the increasing reach to 14.55% at ESTR model with tilt angle 12˚ at tip speed ratio of 7. As well as, these two models provide a jump in power coefficient for a different range of tip speed ratio compare to previous model of ESTR.

Employability of vertical axis crossflow whirlybird rotor as hydrokinetic turbine and its performance prediction corresponding to different design parameters

In this study, the employability of the vertical axis crossflow whirlybird rotor as a hydrokinetic turbine is examined. Further, design parameters are optimized that affect the rotor performance. Torque, power, power coefficient and torque coefficient are calculated at various angular speeds and tip speed ratio (TSR) by Numerical method using computational fluid dynamics (CFD). Further different results of numerical analysis are validated with the experiment. Numerical analysis results shown in the form of pressure contour, velocity contour and velocity vector are served to explain the flow phenomenon surrounding the rotor. Subsequently, effects of the number of blades, blade angle, rotor diameter, rotor height, blade length and free stream velocity on the performance of rotor are also investigated. It is found that with the increase in blade number, blade angle and blade length, the maximum torque coefficient and maximum power coefficient increase up to a certain limit and then drop drastically. In view of these, the optimal blade number, blade angle and blade length are determined as 27, 75 ̊ and 30 mm respectively for the present design configuration of the rotor. Moreover, the analysis suggests that the rotor diameter, height and free stream velocity have a substantial influence on turbine output.

Aerodynamic and aeroacoustic performance investigations on modified H-rotor Darrieus wind turbine

The present paper investigates the aerodynamic and aeroacoustic characteristics of the H-rotor Darrieus vertical axis wind turbine (VAWT) combined with very promising energy conversion and steering technology; a fixed guide-vanes. The main scope of the current work is to enhance the aerodynamic performance and assess the noise production accomplished with such enhancement. The studies are carried out in two phases; the first phase is a parametric 2D CFD simulation employing the unsteady Reynolds-averaged Navier-Stokes (URANS) approach to optimize the design parameters of the guide-vanes. The second phase is a 3D CFD simulation of the full turbine using a higher-order numerical scheme and a hybrid RANS/LES (DDES) method. The guide-vanes show a superior power augmentation, about 42% increase in the power coefficient at λ = 2.75, with a slightly noisy operation and completely change the signal directivity. A remarkable difference in power coefficient is observed between 2D and 3D models at the high-speed ratios stems from the 3D effect. As a result, a 3D simulation of the capped Darrieus turbine is carried out, and then a noise assessment of such configuration is assessed. The results show a 20% increase in power coefficient by using the cap, without significant change in the noise signal.