Power Coefficient Of Turbine Research Articles

Aerodynamic performance optimization of an airfoil-based airborne wind turbine using genetic algorithm

The present manuscript proposes an aerodynamically optimized airfoil-based-shell for performance enhancement of the buoyant airborne turbine system. An integrated code, based on a genetic algorithm, is developed to parametrize the asymmetric airfoil NACA-9415, analyse its aerodynamics and optimize the lift of the airfoil. The 3D steady-state analysis is performed on the optimized shell geometry with NREL-IV rotor using Reynolds Averaged Navier-Stokes (RANS) equation along with k−ωSST turbulence model. The performance of the airborne wind turbine with the optimized shell configuration is assessed in terms of aerodynamic coefficients including shell thrust coefficient, shell back pressure coefficient, turbine power coefficient and power augmentation ratio. The comparison of wind turbine performance with optimized and original NACA-9415 shell configuration demonstrates that shell optimization results in a maximum power coefficient of 1.25 and power augmentation ratio of 2.1 compared to the Betz limit.

Computational analysis of Savonius wind turbine modifications including novel scooplet-based design attained via smart numerical optimization

Simple design and low power coefficient of Savonius-style wind turbines make them attractive in experimental and computational fluid dynamics (CFD) based optimization studies. Still, after numerous studies the power coefficient is low, and the single optimal Savonius-style wind turbine shape and configuration is not known. This leaves room for improving the power coefficient, and the objective of this paper is to find an improved solution with application of smart numerical optimization.Several Savonius blade improvements proposed by other researchers were initially analyzed. The numerical (3D CFD) analysis has shown that simple modifications of the blades can be better than more complicated shapes such as spline or elliptical curve. This has encouraged the investigation on what is the limit to the optimized design which used only simple circular-arc based blades. Thus, we perform a global optimization of Savonius blade pair where each pair is composed of two circular arc segments. The smart numerical optimization was performed using 2D CFD and the results were verified and compared with the previous designs using the 3D CFD. The selected optimization operating conditions were tip speed ratio 0.9 and wind speed 12 m/s. The novel optimized design achieved 39% improvement of the maximum power coefficient relative to the classical Savonius design.

Study on Hydrodynamic Configuration Parameters of Vertical-Axis Tidal Turbine

Abstract In this paper, a numerical code for predicting the hydrodynamic performance of vertical-axis tidal turbine array is developed. The effect of the tip speed ratio, solidity, and preset angle on the hydrodynamic performance are discussed using a series of calculations. The load principle of the rotor and the variation principle of the turbine power coefficient are studied. All these results can be considered as a reference for the design of vertical-axis tidal turbines.

Maximum thermodynamic power coefficient of a wind turbine

AbstractAccording to the centenary Betz‐Joukowsky law, the power extracted from a wind turbine in open flow cannot exceed 16/27 of the wind transported kinetic energy rate. This limit is usually interpreted as an absolute theoretical upper bound for the power coefficient of all wind turbines, but it was derived in the special case of incompressible fluids. Following the same steps of Betz classical derivation, we model the turbine as an actuator disk in a one dimensional fluid flow but consider the general case of a compressible reversible fluid, such as air. In doing so, we are obliged to use not only the laws of mechanics but also and explicitly the laws of thermodynamics. We show that the power coefficient depends on the inlet wind Mach number , and that its maximum value exceeds the Betz‐Joukowsky limit. We have developed a series expansion for the maximum power coefficient in powers of the Mach number that unifies all the cases (compressible and incompressible) in the same simple expression: .

A simple model for deep dynamic stall conditions

AbstractThe present study is focused on modeling of dynamic stall behavior of a pitching airfoil. The deep stall regime is in particular considered. A model is proposed, which has a low implementation and computational complexity but yet is able to deal with different types of dynamic stall conditions, including those characterized by multiple vortex shedding at the airfoil leading edge. The proposed model is appraised against an extensive data set of experimental (α,CL) curves for NACA0012. The results of an existing widely used model, having comparable complexity, are also shown for comparison. The proposed model is able to well reproduce not only the classic curves of deep dynamic stall but also the curves characterized by lift oscillations at high angles of attack due to the shedding of multiple vortices. Furthermore, the model appears to be robust to variations of its parameters from the optimal values and of the airfoil geometry. Finally, the model is successfully implemented in a commercial CFD software and applied to the simulation of a vertical axis wind turbine within the actuator cylinder approach. The accuracy of the prediction of the turbine power coefficient in the whole rotation cycle is very good for the optimal working condition of the turbine, for which the model parameters were calibrated. Fairly good accuracy is also obtained in significantly different working conditions without any further calibration.

Drag coefficient calculation of modified Myring-Savonius wind turbine with numerical simulations

Nowadays the importance of renewable energy is growing, and the utilization of the low wind energy potential is getting crucial. There are turbines with low and high tip speed ratio. Turbines with low tip speed ratio such as the Savonius wind turbine can generate adequate amount of torque at low wind velocities. These types of turbines are also called drag machines. The geometry of the blade can greatly influence the efficiency of the device. With Computational Fluid Dynamics (CFD) method, several optimizations can be done before the production. In our paper the Savonius wind turbine blade geometry was designed based on the so-called Myring equation. The primary objective of this paper was to investigate the drag coefficient of the force acting on the surface of the blade. Also, the Karman vortex was investigated and the space ratio of that vortex in our simulation was compared to a typical one. The power coefficient of a new Savonius turbine was investigated at different values of top speed ratio (TSR). For the sake of simplicity, a 2D cross-sectional area was investigated in the simulation with ANSYS Fluent 19.2.

Three-dimensional Numerical Study of the Performance of a Small Combined Savonius-Darrieus Vertical Wind Turbine

Energy crisis and global warming have encouraged the use of renewable energy resources such as wind power. Among different types of wind turbines, vertical axis wind turbines can be easily installed in residential areas. In this study, a computational fluid dynamics analysis was performed to predict the performance characteristics of three configurations of small vertical axis wind turbines. For this purpose, an shear stress transport k-omega turbulent model and a rotating frame of reference were employed. Initially, a Savonius and a Darrieus wind turbine were simulated; the low power coefficient of the Savonius wind turbine and the poor performance of the Darrieus wind turbine in low tip speed ratios were the main disadvantages of these systems. Finally, a combined Savonius-Darrieus wind turbine was proposed to deal with these drawbacks. The power coefficient of this combined wind turbines was nearly as high as the Darrieus wind turbine (0.3), while the Savonius blades recover the low torque obtained at low tip speed ratios and help produce more consistent torque, making it suitable for residential applications.

Pengaruh rasio konsentrasi pada turbin air Savonius

Irrigation channels have the potential to be used as power plants. Savonius water turbine can be developed because it has a simple construction and is suitable for low speed, according to the characteristics of the irrigation channel. The objectives of the research were to understand the influence of the installation of concentrator the performance of Savonius water turbine. Concentrator can steer the incoming water flow toward the turbine blades that generate positive moments, consequently, the generated power increases. Variations in the concentration ratios studied were 2: 1, 3: 1, and 4: 1. The results show that adding concentrators can increase torque, turbine power and power coefficient. The best performance of the Savonius water turbine showed is with the concentrator ratio of 3:1.

Condensation flow at the wet steam centrifugal turbine stage

This paper investigates spontaneous condensation of wet steam in a centrifugal turbine by means of three-dimensional computational fluid dynamics. The flow field and aerodynamic characteristics of the wet steam in the centrifugal turbine are compared and analyzed by using the equilibrium steam and nonequilibrium steam models, respectively, where the latter applies the classical droplet nucleation theory and neglects velocity slip between the liquid phase and the gaseous phase. The state parameters of wet steam are described here based on the IAPWS’97 formulation. It is concluded that under the design condition, the mass flow rate, wetness fraction, and flow angle of the wet steam centrifugal turbine in the nonequilibrium steam model all change compared with the equilibrium steam model, with values of 4.4%, 0.5%, and 10.57%, respectively. Then the performance variation of the wet steam centrifugal turbine is analyzed under different steam conditions and different outlet back-pressure conditions. The results show that the change law of the mass flow rate, shaft power, and wetness fraction in the centrifugal turbine are basically identical in both models, and the mass flow rate, shaft power, wheel efficiency, and entropy loss coefficient of the centrifugal turbine in the nonequilibrium steam model are all higher than those in the equilibrium steam model, whereas the outlet wetness fraction is lower than that in the equilibrium steam model.

The aerodynamic performance of H-type darrieus VAWT rotor with and without winglets: CFD simulations

ABSTRACT In this study, the H-Rotor vertical axis wind turbines with and without winglets are simulated by ANSYS CFX software based on structured meshing technology and incompressible continuity Reynolds Averaged Navier-Stokes equations (RANS) solver. It is shown that the CFD and experimental results of the rotor power coefficient have a good agreement during the range of calculations. The rotor power coefficient of H-type vertical axis wind turbine with winglets is 10% to 19% higher than that of the original H-type vertical axis wind turbine. In each revolution, the output torque of H-type vertical axis wind turbine with winglets is larger than that of the original H-type vertical axis wind turbine at every azimuth angle; the maximum torque increases by 12.8% and the negative torque is avoided when tip ratio reaches 1.53; the minimum and maximum thrust increase by 26.7% and 3.4%. The vorticity distribution at the tips of wingletted H-Rotor blades are weaker than the H-Rotor without winglets. The aerodynamic performance of the near region of blade tips is improved. Winglets increase the overall torque-generating, but does not improve it at every azimuth angle for each blade. The reported results may provide a valuable reference or benchmark for the design and optimization of future wingletted H-Rotor VAWTs.

Effect of blade number and angle on the characteristics of the savonius type wind turbine

The savonius type vertical axis wind turbine can be operated in all wind directions, is low cut in speed and high in torque. Therefore, it is a potential source of energy in low wind areas. This research aimed to compare the performance of H-Savonius vertical axis wind turbine using blades numbers and blades angle. The turbine containing the blades numbers 4, 6, 8, 12, 16 and 18 with the blades angle being at -15°, -5°, 0°, 5° and 15°, respectively. Tests were undertaken at open type circuit wind tunnel. The results showed that the maximum power coefficient of the wind turbine at 16 blades and angle of 5° with an average of 0.26 which had 4.5 % increase in power compared to that of turbines the baseline. Finally, the cut in wind speed and the rev up time was 2.32 m/s and 25 s, respectively.

Effect of rotor tip clearance on the aerodynamic performance of an aerofoil-based ducted wind turbine

With the increase in world energy demands, the focus has been shifted toward renewable energy sources. Wind energy has been investigated as a viable source of energy in recent years and several new design concepts have been introduced to benefit from high-speed winds at higher altitudes. Buoyant airborne turbine (BAT) is a similar concept designed to exploit high altitude winds by lifting the whole wind turbine system within a toroidal shaped shell filled with helium. The present study investigates the aerodynamic performance of the BAT shell based on a NACA-9415 airfoil with different rotor blade tip clearances. Three-dimensional analysis has been conducted considering a two-bladed NREL Phase IV rotor at a variety of wind speeds for the tip gaps ranging from 1% to 5% of the shell throat radius. The influence of the blade tip clearance on the turbine performance has been explored by analysing wind turbine aerodynamic coefficients, swallowed mass flow rate and wake generated behind the wind turbine. The results showed a declining trend in the wind turbine power coefficient with the increment in tip clearance for the wind speeds of 10 m/s–20 m/s. However, at the higher wind speed, the turbine power coefficient demonstrated a direct association with the tip clearance for the tip gaps of 1%-3% followed by a drop in the turbine power coefficient at the wider tip clearance.

Performance investigation of dual shaft hybrid vertical turbines using directional fins

The current direction of wind turbine development is more on horizontal wind turbine types because of its efficiency, which is better than vertical wind turbines. But there are some advantages of this vertical wind turbine in the kind of array turbines and small-sized turbines. In this paper, the research focuses on developing a vertical wind turbine between Savonius and Darrieus turbines and has a dual shaft on one wind energy generating unit.Vertical turbine design with two turbine shafts placed close together is intended to increase turbine efficiency and increase power density. But this design also affects the omnidirectional nature of the vertical single shaft turbine.This research investigates the change in the omnidirectional nature of the hybrid vertical turbine dual shaft design and the influence of models of a fin to restore the properties of the omnidirectional turbine. Then tests the performance between prototype using the directional fins and without using the directional fins.Omnidirectional nature is one of the advantages in vertical turbines, but in the design with two axes, the omnidirectional nature changes and can affect the overall vertical turbine performance.The experiment results show that the vertical shaft hybrid turbines still have omnidirectional properties, and the use of fins increases the TSR (Tips Speed ratio) value of wind speed, increases the Cp (Power coefficient) of the wind turbine and increases the mechanical power potential of the turbine.

Dynamic Stall of a Vertical-Axis Wind Turbine and Its Control Using Plasma Actuation

In this paper, a dynamic stall control scheme for vertical-axis wind turbine (VAWT) based on pulsed dielectric-barrier-discharge (DBD) plasma actuation is proposed using computational fluid dynamics (CFD). The trend of the wind turbine power coefficient with the tip speed ratio is verified, and the numerical simulation can describe the typical dynamic stall process of the H-type VAWT. The tangential force coefficient and vorticity contours of the blade are compared, and the regular pattern of the VAWT dynamic stall under different tip speed ratios is obtained. Based on the understanding the dynamic stall phenomenon in flow field, the effect of the azimuth of the plasma actuation on the VAWT power is studied. The results show that the azimuth interval of the dynamic stall is approximately 60° or 80° by the different tip speed ratio. The pulsed plasma actuation can suppress dynamic stall. The actuation is optimally applied for the azimuthal position of 60° to 120°.

Lift-type and drag-type hydro turbine with vertical axis for power generation from water pipelines

Pipeline turbines are designed to supply power for smart sensors installed in water pipelines. They are installed in the water supply pipe network directly and should meet the performance requirements for starting up at low flow rates and having low pressure loss at high flow rates. To this end, we designed two types of vertical axis pipeline turbines with lift-type runner and drag-type runner respectively, and conducted both experimental test and numerical simulations on the hydraulic performance of both the turbines. The results show that both the lift-type and drag-type turbines can meet the performance requirements. Under the same incoming flow conditions, the critical startup flow rate, the tip speed ratio, and the power coefficient of the lift-type turbine is larger. And the startup process of the lift-type turbine is unstable. While the drag-type turbine shows the opposite performances in these respects. In the range of incoming flow velocity studied, the pressure loss of both the turbines increases with the incoming flow velocity, however, the maximum pressure loss is controlled in an acceptable range, which will not affect the normal water supply.

A blade pitching approach for vertical axis wind turbines based on the free vortex method

This paper presents a variable pitch (VP) approach for a vertical axis wind turbine running at rated or higher tip speed ratios (TSRs) in order to improve the blade aerodynamic performance at the azimuth angle with a low angle of attack (AoA) and the peak power coefficient (Cp) of the wind turbine. The four largest pitch angles occurred in each quadrant in the proposed VP approach, whereas the two largest pitch angles occurred at azimuth angles of 90° and 270° n the traditional VP approaches. The free vortex model was used to predict the aerodynamic performances of the blades in the proposed VP approach and the fixed pitch (FP) blade at the designed TSR. The circulation of different vortices, the AoA, the induced velocity, and the lift coefficient obtained from the modeling results were compared for the different methods. The results indicated differences in the strength of the bound vortex and the shed vortex between the VP and FP blades at different azimuth positions. The range of the largest AoAs in the VP blade was in two big scopes, whereas the largest AoAs in the FP blade occurred only at two azimuth positions. The torque and the Cp increased at different azimuth angles, and similar trends of the AoA were observed in the azimuth angle range of 0°–360°. The differences between the VP and FP blades provided in-depth information on the performance of the proposed VP approach. The integration of the proposed VP approach and the traditional approach provides a VP strategy to control the pitch angle of the blade based on the azimuth angles and the TSRs and results in better self-starting ability at low TSRs and greater Cp at various TSRs.

Experimental validation of the power enhancement of a pair of vertical-axis wind turbines

Wind tunnel tests have been performed of individual and paired H-type Darrieus vertical-axis wind turbines. The turbines in the paired configuration are closely spaced, at 1.2 and 1.3 rotor diameters shaft to shaft, and are counter-rotating. Two directions of rotation were studied, one where the facing (inner) blades move along with the incoming flow, and one where the facing blades move against the wind. The wind tunnel tests confirm a net increase in the power coefficient of the paired configuration compared with twice the power coefficient of the individual turbine. We found average relative increases in the power coefficients between 13% and 16%, which is consistent with numerical studies available in the literature.

Effect of blade pitching on power coefficient of small-scale vertical axis wind turbine at different tip speed ratios

This article analyses the effect of best blade pitching positions on the power coefficient of vertical axis wind turbine at different tip speed ratios. Analysis of the power coefficient of the vertical axis wind turbine is carried out for optimized six blade pitching curves. The first three pitching curves are designed for the tip speed ratios below 1.5 (0 < λ < 1.5) and other three are for the tip speed ratios in the range of 0 < λ < 3. The double multiple stream tube model is used for the present analysis. The results are compared between the optimized and sinusoidal pitching curves. It is concluded that the best optimized pitch position blade method improves the power coefficient than the typical sinusoidal blade pitching in the range of tip speed ratios 0 < λ < 3.

On the accuracy of turbulence models for CFD simulations of vertical axis wind turbines

A comparative analysis of seven commonly-used eddy-viscosity turbulence models for CFD simulations of VAWTs is presented. The models include one- to four-equations, namely the Spalart-Allmaras (SA), RNG k-ε, realizable k-ε, SST k-ω, SST k-ω with an additional intermittency transition model (SSTI), k-kl-ω and transition SST (TSST) k-ω models. In addition, the inviscid modeling is included in the comparison. The evaluation is based on validation with three sets of experiments for three VAWTs with different geometrical characteristics operating in a wide range of operational conditions, from dynamic stall to optimal regime and to highly-rotational flow regime. The focus is on the turbine wake, the turbine power performance, and the blade aerodynamics. High-fidelity incompressible unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations are employed. The extensive analysis reveals high sensitivity of the simulation results to the turbulence model. This is especially the case for the turbine power coefficient CP. The results show that the inviscid, SA, RNG k-ε, realizable k-ε and k-kl-ω models clearly fail in reproducing the aerodynamic performance of VAWTs. Only the SST model variants (SST k-ω, SSTI and TSST) are capable of exhibiting reasonable agreement with all the experimental data sets, where the transitional SST k-ω versions (SSTI and TSST) are recommended as the models of choice especially in the transitional flow regime.

Experimental and analytical analysis of vaned savonius turbine performance under different operating conditions

Global energy production is shifting towards more distributed technologies, where power generation takes place close to people. A vaned Savonius wind turbine is one of the possible solutions, which can fulfil the requirements of being simultaneously reliable, safe and non-disturbing. One challenge is that when the size of the turbine becomes smaller and the wind velocity is low, the Reynolds number effects begin to deteriorate the performance. Public literature lacks detailed information about how the turbine performance and internal flows change in these conditions. In this work, a vaned Savonius turbine is tested in a wind tunnel with seven Reynolds numbers and several tip-to-speed ratios. The measurements include both the turbine performance and the static pressures inside the vane passages. All experiments are also conducted separately for the stator only configuration to evaluate the effects of stator-rotor interaction. The main results are: (1) a new Reynolds number-dependent performance prediction correlation is developed with an achievable accuracy of ±5%, (2) Savonius turbine power coefficient follows the trend of kinetic compressors relatively well and due to the changing Reynolds number, an over 20% drop in vaned turbine performance can be observed, (3) the Reynolds number affects performance through friction and flow separations, but the vane passage pressure distributions are not affected and (4) tip-to-speed ratio affects the vane passage pressure distribution via stator-rotor interaction. It is also suggested that the nominal tip-to-speed ratio should be kept relatively low in the design phase to minimise the negative effects of stator-rotor interaction.