Variation Of Power Coefficient Research Articles

Experimental and numerical investigation into effect of different blade configurations on performance of small-scale wind turbines

Experimental investigations and numerical analysis using Ansys CFD software of the effect of different blade configurations on the performance of small-scale wind turbines are presented in this paper. A complete test rig of small-scale wind turbine is built, and three-dimensional computational model of the rotor system is created and simulated using Realizable K−ε turbulent model to evaluate the performance of four types of blade configurations (Twisted blades with NACA0012, Straight (untwisted) blades with NACA0012, Twisted blades with NACA4418, Straight (untwisted) blades with NACA4418). The experimental and numerical analysis has been carried out at various wind speeds in the range of 2 m/s to 8 m/s to study the variation of power coefficient for different configurations of blades with wind speed and choose the most effective design of blades. The results show that the numerical solution over predicts the power produced compared to the experimental test field for all tested blades configurations. The maximum deviation was around 15 percent between the numerical and experimental results and decreased with increasing wind speed. Untwisted blades with NACA0012 are the most effective design of blades suitable for small scale wind turbine based on numerical and experimental results, giving an average of actual power coefficient (Cp = 0.41). Compared to all tested configuration, this design is simple in manufacturing with minimum cost.

Effects of blade shape and its corresponding moment of inertia on self-starting and power extraction performance of the novel bowl-shaped floating straight-bladed vertical axis wind turbine

In this paper, the effects of the blade shape and its corresponding moment of inertia on the performance of a novel bowl-shaped floating straight bladed vertical axis wind turbine (VAWT) have been investigated. A numerical method was developed and validated to accurately simulate the interaction between the wind and VAWT. Three inferential parameters, the starting time, mean power coefficient, and standard deviation of the aerodynamic force, were employed to evaluate the performance of the turbine with different blade shapes. Performance indicators including the self-starting capability, power extraction efficiency, and fatigue characteristics, were assessed. The results indicated that the VAWT with S-1046 blade had better overall performance as compared to the one with NACA0018 blade, where the reduced self-starting time, slight more or identical mean power coefficient, and minor standard deviation of Ft and Fn were observed. Further, the flow structure around the blade was also analyzed, it was found that at low wind speed (less than 6.0 m/s) separated vortex around the turbine is observed, whereas at high wind speed, attached vortex is observed. Fluctuation curves of power coefficient variation with tip speed ratio ‘λ’ were also noted for the wind induced rotation of VAWT. At low wind speed, the highest power coefficient amplitude was obtained when the turbine was at maximum tip speed ratio, whereas at high wind speed, the highest power coefficient amplitude was obtained when the tip speed ratio of the turbine was slight less than the maximum value. Based on these results, it is strongly recommended to apply thinner symmetry (S-1046) blade for designing VAWT.

On Blockage Effects for a Tidal Turbine in Free Surface Proximity

Experiments with a three-bladed, constant chord tidal turbine were undertaken to understand the influence of free surface proximity on blockage effects and near-wake flow field. The turbine was placed at various depths as rotational speeds were varied; thrust and torque data were acquired through a submerged sensor. Blockage effects were quantified in terms of changes in power coefficient and were found to be dependent on tip speed ratio and free surface to blade tip clearance. Flow acceleration near turbine rotation plane was attributed to blockage offered by the rotor, wake, and free surface deformation. In addition, particle image velocimetry was carried out in the turbine near-wake using time- and phase-averaged techniques to understand the mechanism responsible for the variation of power coefficient with rotational speed and free surface proximity. Slower wake propagation for higher rotational velocities and increased asymmetry in the wake with increasing free surface proximity was observed. Improved performance at high rotational speed was attributed to enhanced wake blockage, and performance enhancement with free surface proximity was due to the additional blockage effects caused by the free surface deformation. Proper orthogonal decomposition analysis revealed a downward moving wake for the turbine placed in near free surface proximity.

Numerical efficiency evaluation of a vertical axis turbine equipped with 4 digits and 5 digits NACA airfoils

In the current age of global energy crisis, a run for the use of renewable energy resources as the wind energy has gained a significant attention. The main objective of this study is the comparison between two wind turbine configurations. These two turbines have the same geometric parameters but one with a 4 digits NACA0018 blades and the other with 5 digits NACA63-415 blades. In this scientific paper, a numerical evaluation of the airfoil shape influence on the VAWT efficiency is done. For this study the CFD methods with Ansys Fluent software, are used. All the simulations are for unsteady flow at 1e06 Reynolds number value with SST turbulence model. At the design point the wind velocity is 12 m/s and for the wind turbine geometric features, the diameter is 3.25m and the height 4.87m. The power coefficient variation through tip speed ratio will be represented for each wind turbine configurations. To estimate the recirculation zone effects on the efficiency, the vorticity magnitude contours are presented for different positions of the blades. The results will indicate the feasibility of optimization of future wind turbine more complex airfoils.

Effect of number of blades in ducted turbine system on kinetic energy extraction from chimney flue gases – benchmarking with wind energy system

A multi-blade ducted wind turbine, also called the diffuser augmented wind turbine (DAWT) has a good wind energy conversion effect over the traditional wind turbine. The market potential for energy recovery from the chimney flue gases made it necessary to explore the possibility of extraction of the energy from flue gases using the DAWT. The duct is a converging-diverging nozzle with the turbineblades located at the throat. In general 3 or more number of blades is frequently used to maximize the energy conversion to the bladetorque. The effect of number of blades on the power extraction by the energy recovery ducted turbine has been studied in this paper. A CFD-based simulation study has been carried out. The results so obtained have been benchmarked with the published data for the results for the ducted turbines for wind power generation. The general airfoil NACA4420, NACA4416 and NACA4412 were adopted to produce various composite profiles for turbine-blade. The large number of blades appears to provide the sufficient blade areas for the conversion of energy of flue gases to the turbine-rotor torque. On other hand the more number of blades also increases the blockage to the flue gases, resulting in increased back-flow. This paper presents the variation of power coefficient (CP) and torque coefficient (CT) with respect to the tip speed ratio (λ) for different number of blades, and varying blade geometry.

Evaluation of Energy in Wind Turbine System Using Probability Distribution

In this work, annual energy output of a variable speed wind turbine is analyzed using annual Weibull wind speed probability distribution function. The power coefficient variety with tip speed proportion in torque control district and pitch point variety for most extreme power yield from wind turbine are examined for distinguishing control framework parameters. The wind turbine power output and variation of power coefficient with tip speed ratio as well as pitch angle are examined / reported using annual Wei bull distribution function. Finally the variation of the estimated annual energy output of the given wind turbine with the mean wind speed is presented.

Near wake region of an industrial scale wind turbine: comparing LES-ALM with LES-SMI simulations using data mining (POD)

Accurate prediction of power generation capability needs proper assessment of blade loading and wake behavior. In this regard, the Sliding Mesh Interface (SMI) approach and the Actuator Line Model (ALM) are two diverse computational fluid dynamics (CFD) based approaches of simulating the turbine behavior, each having its own merits and demerits. The SMI technique simulates the unsteady flow by explicitly modeling the blades and their rotation using a dynamic mesh, while in Actuator Line Model, the blades are not modeled explicitly but each blade is resolved as a rotating line (made of N actuator segments), over which the forces are computed. The current work focuses on simulating an industrial scale reference turbine and in differentiating the near wake dynamics predicted by these two approaches using Large Eddy Simulation (LES) and Proper Orthogonal Decomposition (POD) technique (a data mining tool). Initially, the ALM is compared with FAST model for the prediction of variation of power coefficient with the Tip Speed Ratio (TSR). The ALM is able to capture the varying trend and it predicts a similar optimum tip speed ratio as the FAST model. At this optimum TSR condition, the ALM is compared with the SMI method for a study limited to the near wake region. Comparisons between SMI and ALM shows that : (a) The SMI is predicting more complex 3D nature of the flow, and (b) the POD shows that ALM captures the shear regions of wake but it does not capture the vast compendium of length and time scales of eddies as SMI does. However, despite these limitations, the ALM has been able to capture the qualitative trend in wake deficit and the power coefficient variation with tip speed.

Computational Fluid Dynamics Investigation of a Novel Multiblade Wind Turbine in a Duct

A novel manufacturing approach similar to filament winding is able to produce high-performance and lightweight composite wheels. The production can be rapid, inexpensive, and utilize commercially available winding machines. One potential application of the wheel is as a wind turbine. It is widely accepted that placing a duct around a wind turbine can enhance its performance, especially when a new designed turbine with unique advantages has a relatively low power coefficient, it is necessary to examine the benefits and economics of a turbine in a duct. In this study, a numerical analysis of a ducted multiblade composite wind turbine using computational fluid dynamics (CFD) is evaluated and compared with a bare wind turbine of the same turbine area. This investigation was performed using FLUENT in conjunction with the GAMBIT meshing tool. The extracted power is calculated and compared for these two modeling designs. Through the comparison of power coefficient variation with thrust coefficient, it was found that a ducted turbine can be 2–3 times that of the power extracted by a bare turbine. The results of the analysis provide an insight into the aerodynamic design and operation of a ducted wind turbine in order to shorten the design period and improve its technical performance.

Experimental study of yawed inflow around wind turbine rotor

In this article, we present an experimental study in a wind tunnel of a three-bladed, Rutland 503 model, horizontal axis yawed wind turbine. Power measurement and an exploration downstream wake of the turbine using particle image velocimetry measurements are performed. The variation of power coefficient as a function of rotational velocity is presented for different yaw angles. The results show a loss of power from the wind turbine when the yaw angle increases. The velocity field of the downstream wake of the rotor is presented in an azimuth plane, which passes through the symmetry axis of the rotor. The instantaneous velocity field is measured and recorded to allow for obtaining the averaged velocity field. The results also show variations in the wake downstream due to decelerating flow caused by the yawed turbine rotor. Analysis of this data shows that the active control of yaw angles could be an advantage to preserve the power from the wind turbine and that details near rotor wake are important for wake theories and to predict the performance of wind turbines as well.

Effect of rotor blade position on Vertical Axis Wind Turbine Performance

The need for sustainable energy sources becomes greater each year due to the continued depletion of fossil fuels and the resulting energy crisis. For the past decade there has been a call for immediate and concrete solutions to the climatic challenges the world is currently facing. An answer to the need for a sustainable, low cost energy solution is potentially in the form of wind turbines, which are receiving increased political support. In this paper a numerical study is presented with the aim of evaluating the performance output of three Vertical Axis Wind Turbine (VAWT) configurations. Here using Computational Fluid Dynamics (CFD) a two-dimensional Multi Reference Frame (MRF) approach has been used to perform steady state simulations. For this purpose an inlet velocity of 4m/s has been used along with rotor blade tip speed ratios (λ) in the range of 0 to 0.6. The effects of varying rotor blade position on the global and local flow fields have been quantified as shown in Figure.1. Figure.1 ’Pressure field (Pa) with rotor at 0°, λ=0.4’ From this figure it can be seen that the pressure distribution across the wind turbine is non uniform and features large pockets of high and low pressure. The regions of the turbine that are in direct contact with the air stream (windward) feature the highest pressure. It is also evident that each blade has both a pressure and a suction side. The torque contribution made by each rotor blade for each rotor position is presented in Figure.2. This contribution has been non-dimensionalised relative to overall rotor torque output (T/TAVG). Figure.2 ’Variation of rotor blade torque (T/TAVG) contribution at R=0,10 and 20 ’ Here, the rotor blade passage between blades 11 and 12 generates maximum torque when the rotor is at 20 . Furthermore, it has been found that within a typical rotor blade passage, maximum torque is obtained at a unique rotor angle. The power curves for all three configurations are depicted in Figure.3 and show the variation of power coefficient with respect to TSR. From the data obtained it can be concluded that the VAWT power curve characteristics vary with relative rotor blade position. For positions 10 and 20 peak power is generated at a tip speed ratio of 0.4 whereas position 0 generates maximum power at 0.6. A maximum power coefficient of 0.26 is present when the rotor is positioned at 0 and operating at a tip speed ratio of 0.6. Figure.3 ‘Variation of power output with respect to λ’

On the aerodynamic performance of a class of vertical shaft windmills

A theory is presented to estimate the aerodynamic performance of a vertical shaft windmill configuration recently developed by South & Rangi (1971, 1972). The induced velocity is assumed to be given by simple momentum theory arguments; a blade element analysis then yields equa­tions from which the mean power coefficient may be calculated. If the induced velocity is assumed to be uniform the predicted power coefficients are somewhat high compared to the experimental results. It is shown that the uniform induced velocity theory can be linearized for high tip speed ratios, to yield a simple formula for the mean power coefficient, C' P = σμ' ( A 0 — A 1 μ' 2 ), where σ is the blade solidity, μ' is the tip speed ratio based on the local wind speed and A 0 and A 1 are constants determined by the blade geometry. Further, guided by the refinements earlier made to propeller theory, an analysis incorporating non-uniform induced velocity over the windmill disk is presented. These calculations, when compared with the uniform induced velocity calculations, lead to a reduction in the power coefficient for tip speed ratios corresponding to the peak power coefficient and greater. Finally, when compared with the available experimental data, the calcula­tions show encouraging agreement as regards the peak power coefficient, the effect of blade solidity and the variation of power coefficient with tip speed ratio.