The Experts below are selected from a list of 24798 Experts worldwide ranked by ideXlab platform
Manhoe Kim - One of the best experts on this subject based on the ideXlab platform.
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unsteady aerodynamic performance analysis of an airborne wind turbine under load varying conditions at high altitude
Energy Conversion and Management, 2020Co-Authors: Qazi Shahzad Ali, Manhoe KimAbstract:Abstract The blade air loads of the Airborne Wind Turbine (AWT) may be significantly influenced by the unsteady flow-field at high altitude. Under these susceptible situations, the Rotor needs in-depth considerations with respect to transient aspects. The present study focuses on the unsteady aerodynamic performance of stand-alone Rotor under the influence of wind shear, yawed, and tilted configurations. The Computational Fluid Dynamics (CFD) transient simulations based on the sliding mesh approach are carried out for analyzing the unsteady behavior of the Rotor by lifting the Rotor assembly at an airborne altitude from the ground. All simulations are conducted at optimal operating conditions of wind speed and tip speed ratio. In-house Unsteady Blade Element Momentum (UBEM) code using the wind shear, dynamic stall, dynamic wake, and yaw /tilt model are applied to acquire an empirical assessment in terms of Rotor Torque, thrust, and power coefficient. Finally, the CFD simulated results are compared against the performance curves generated by the UBEM model and acceptable agreement is found within 4.1% deviation at peak operational conditions. The results further reveal that the time-varying aerodynamic loads on the Rotor blade gradually achieve steady behavior after three rotation periods. Meanwhile, unique similarities are found in yawed and tilted inflow cases and a 10.7% loss in power coefficient is observed due to Rotor yawed inflows. Additionally, in the absence of tower shadows, the strong flow interactions around the Rotor blade impose a positive impact on power output. Despite the complexity of unsteady flow phenomena, this present study would be helpful to design a more proficient airborne Rotor under the varying load conditions.
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effect of Rotor axial position on the aerodynamic performance of an airborne wind turbine system in shell configuration
Energy Conversion and Management, 2017Co-Authors: Arslan Saleem, Manhoe KimAbstract:Abstract Wind energy has been one of the most widespread types of intermittent renewable energy harvesting source. Airborne wind turbine (AWT) stands out among other available techniques for harvesting wind energy because of its ability to operate at multiple times higher altitudes. This paper presents the aerodynamic performance of an AWT system at an altitude of 400 m with NREL Phase IV Rotor position variation within the buoyant shell. The unsteady numerical simulations have been carried out at Rotor axial positions of 0.25 L, 0.3 L, 0.35 L, 0.4 L and 0.45 L (L is the shell length) from the inlet, in order to investigate Rotor Torque variation in one complete Rotor revolution. Additionally, steady-state simulations of the AWT system have been performed at various wind speeds ( 7 m / s – 20 m / s ) and yaw angles ( 0 ° – 15 ° ) , to investigate the optimum aerodynamic performance of buoyant shell and Rotor. Results demonstrate that by placing the Rotor at the shell inlet (0.25 L) with step placed at the shell outlet, maximum Torque enhancement of 25.3% can be attained at wind speed of 15 m / s . Buoyant shell exhibits equilibrium at 0 ° yaw angle due to symmetric pressure distributions on the shell body. Whereas for yaw angle > 0 ° , instability instigated by non-uniform pressure distributions results in the oscillation of shell. However restoring Torque damps out these vibrations and provides assistance in re-establishing equilibrium position.
Naveed Durrani - One of the best experts on this subject based on the ideXlab platform.
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wind tunnel and numerical study of a small vertical axis wind turbine
Renewable Energy, 2010Co-Authors: Robert Howell, Ning Qin, Jonathan Edwards, Naveed DurraniAbstract:Abstract This paper presents a combined experimental and computational study into the aerodynamics and performance of a small scale vertical axis wind turbine (VAWT). Wind tunnel tests were carried out to ascertain overall performance of the turbine and two- and three-dimensional unsteady computational fluid dynamics (CFD) models were generated to help understand the aerodynamics of this performance. Wind tunnel performance results are presented for cases of different wind velocity, tip-speed ratio and solidity as well as Rotor blade surface finish. It is shown experimentally that the surface roughness on the turbine Rotor blades has a significant effect on performance. Below a critical wind speed (Reynolds number of 30,000) the performance of the turbine is degraded by a smooth Rotor surface finish but above it, the turbine performance is enhanced by a smooth surface finish. Both two bladed and three bladed Rotors were tested and a significant increase in performance coefficient is observed for the higher solidity Rotors (three bladed Rotors) over most of the operating range. Dynamic stalling behaviour and the resulting large and rapid changes in force coefficients and the Rotor Torque are shown to be the likely cause of changes to Rotor pitch angle that occurred during early testing. This small change in pitch angle caused significant decreases in performance. The performance coefficient predicted by the two dimensional computational model is significantly higher than that of the experimental and the three-dimensional CFD model. The predictions show that the presence of the over tip vortices in the 3D simulations is responsible for producing the large difference in efficiency compared to the 2D predictions. The dynamic behaviour of the over tip vortex as a Rotor blade rotates through each revolution is also explored in the paper.
Ernesto Benini - One of the best experts on this subject based on the ideXlab platform.
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effect of blade inclination angle on a darrieus wind turbine
Journal of Turbomachinery-transactions of The Asme, 2012Co-Authors: Marco Raciti Castelli, Ernesto BeniniAbstract:This paper presents a model for the evaluation of energy performance and aerodynamic forces acting on a small helical Darrieus vertical axis wind turbine depending on blade inclination angle. It consists of an analytical code coupled to a solid modeling software capable of generating the desired blade geometry depending on the desired design geometric parameters, which is linked to a finite volume CFD code for the calculation of Rotor performance. After describing and validating the model with experimental data, the results of numerical simulations are proposed on the bases of five machine architectures, which are characterized by an inclination of the blades with respect to the horizontal plane in order to generate a phase shift angle between lower and upper blade sections of 0 deg, 30 deg, 60 deg, 90 deg, and 120 deg for a Rotor having an aspect ratio of 1.5. The effects of blade inclination on tangential and axial forces are first discussed and then the overall Rotor Torque is considered as a function of azimuthal position of the blades. Finally, the downstream tip recirculation zone due to the finite blade extension is analyzed for each blade inclination angle, achieving a numerical quantification of the influence of induced drag on Rotor performance, as a function of both blade element longitudinal and azimuthal positions of the blade itself.
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the darrieus wind turbine proposal for a new performance prediction model based on cfd
Energy, 2011Co-Authors: Marco Raciti Castelli, Alessandro Englaro, Ernesto BeniniAbstract:This paper presents a CFD model for the evaluation of energy performance and aerodynamic forces acting on a straight-bladed vertical-axis Darrieus wind turbine. The basic principles which are currently applied to BE-M theory for Rotor performance prediction are transferred to the CFD code, allowing the correlation between flow geometric characteristics (such as blade angles of attack) and dynamic quantities (such as Rotor Torque and blade tangential and normal forces). The model is proposed as a powerful design and optimization tool for the development of new Rotor architectures for which test data is not available.
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the darrieus wind turbine proposal for a new performance prediction model based on cfd
Energy, 2011Co-Authors: Marco Raciti Castelli, Alessandro Englaro, Ernesto BeniniAbstract:Abstract This paper presents a CFD model for the evaluation of energy performance and aerodynamic forces acting on a straight-bladed vertical-axis Darrieus wind turbine. The basic principles which are currently applied to BE-M theory for Rotor performance prediction are transferred to the CFD code, allowing the correlation between flow geometric characteristics (such as blade angles of attack) and dynamic quantities (such as Rotor Torque and blade tangential and normal forces). The model is proposed as a powerful design and optimization tool for the development of new Rotor architectures for which test data is not available. After describing and validating the computational model against experimental data, a full campaign of simulation is proposed for a classical NACA 0021 three-bladed Rotor. Flow field characteristics are investigated for several values of tip speed ratio, allowing a comparison among Rotor operation at optimum and lower C p values, so that a better understanding of vertical-axis wind turbines basic physics is obtained.
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effect of blade inclination angle on a darrieus wind turbine
Volume 5: Industrial and Cogeneration; Microturbines and Small Turbomachinery; Oil and Gas Applications; Wind Turbine Technology, 2010Co-Authors: Marco Raciti Castelli, Ernesto BeniniAbstract:This paper presents a model for the evaluation of energy performance and aerodynamic forces acting on a small helical Darrieus vertical axis wind turbine depending on blade inclination angle. It consists of an analytical code coupled to a solid modeling software, capable of generating the desired blade geometry depending on the desired design geometric parameters, which is linked to a finite volume CFD code for the calculation of Rotor performance. After describing and validating the model with experimental data, the results of numerical simulations are proposed on the bases of five machine architectures, which are characterized by an inclination of the blades with respect to the horizontal plane in order to generate a phase shift angle between lower and upper blade sections of 0°, 30°, 60°, 90° and 120° for a Rotor having an aspect ratio of 1.5. The effects of blade inclination on tangential and axial forces are first discussed and then the overall Rotor Torque is considered as a function of azimuthal position of the blades. Finally, the downstream tip recirculation zone due to the finite blade extension is analyzed for each blade inclination angle, achieving a numerical quantification of the influence of induced drag on Rotor performance, as a function of both blade element longitudinal and azimuthal positions of the blade itself.Copyright © 2010 by ASME
Länger-möller Annika - One of the best experts on this subject based on the ideXlab platform.
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Development of an interface to introduce stationary LES data to the URANS solver THETA for HAWT performance prediction
'Wiley', 2020Co-Authors: Länger-möller AnnikaAbstract:The impact of different sheared velocity profiles on the performance prediction of a horizontal axis wind turbine in the atmospheric boundary layer is investigated. Firstly, the wall roughness in the analytical logarithmic description of the atmospheric boundary layer is varied to obtain different velocity profiles. Subsequently, it is proposed to replace the analytical logarithmic description of the atmospheric boundary layer by the time‐averaged velocity data of a precursor large eddy simulation (LES) and to reconstruct the turbulence of the velocity fluctuations. The LES data are introduced as inflow condition through a LES‐RANS interface in a one‐way coupling approach. Three different methods to reconstruct URANS turbulence values out of the velocity fluctuations are investigated. It is shown that the reconstruction method has an impact on the development of the velocity profile, turbulent kinetic energy, and the turbulent dissipation during the transport through the URANS domain. The different inflow data, which the horizontal axis wind turbine experiences, are responsible for changes in the overall Rotor thrust (up to 2.7%) and Rotor Torque (up to 2.4%). Conversely, the induction factors and effective angles of attack hardly change and can well be compared with a blade element momentum method. Finally, the results of both approaches to prescribe the atmospheric boundary layer are compared. The thrust and power coefficients, and wake recovery are close to each other. Simulations are carried out on an industrial 900 kW wind turbine with the incompressible URANS solver THETA
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Impact of wall roughness and turbulence level on the performance of a horizontal axis wind turbine with the U‐RANS solver THETA
'Wiley', 2019Co-Authors: Länger-möller AnnikaAbstract:The presented work investigates the impact of different sheared velocity profiles in the atmospheric boundary layer on the characteristics of a wind turbine by modifying the wall roughness coefficients in the logarithmic velocity profile. Moreover, the Rotor and wake characteristics in dependence of the turbulence boundary conditions are investigated. In variant I, the turbulence boundary conditions are defined in accordance to the logarithmic velocity profile with different wall roughness lengths. In variant II, the turbulent kinetic energy and turbulent viscosity remain independent of the velocity profile and represent the free‐stream turbulence level. With an increase of the shear in the velocity profile, the amplitudes in the 3/rev characteristics of Rotor thrust and Rotor Torque, induction factors, and effective angles of attack are increased. In variant I, the overall levels of thrust coefficient are hardly affected by the velocity profiles resulting from different wall roughness length values. The power coefficient is reduced about 1%. Conversely, compared with variant II, a difference of 2% in the power coefficient has been detected. Moreover, the wake recovery process strongly depends on the turbulence boundary condition. Simulations are carried out on an industrial 900‐kW wind turbine with the incompressible U‐RANS solver THETA
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Simulation of transient gusts on the NREL5 MW wind turbine using CFD
2017Co-Authors: Länger-möller AnnikaAbstract:Wind turbines operate in unsteady wind conditions that are caused by the terrain and the atmospheric boundary layer which results in statistical fluctuating inflow conditions. Both effects are studied in CFD studies throughout literature, as lately by Castellani et al. Conversely, the specific investigations of single unsteady events as (large) longitudinal transient gusts are rare. Thus, the performed work presents a procedure, implemented in the CFD-solver THETA, to propagate longitudinal transient gusts through a flow field. In a first attempt, the gust is modelled in a cosines shape that strikes the generic NREL 5MW wind turbine at rated operating conditions and lasts about 6 seconds. Thereafter, the capability to simulate the aforementioned wind turbine under an extreme operating gust, following the international standard IEC 61400-13 definition, is presented. The smooth cosines curve is interrupted by the 3/rev characteristic which is caused by respecting the tower during modelling. Moreover, the moderate gust speeds of ±0.5m/s lead to noticeable changes in Rotor Torque. The flow states on the Rotor blade before the gust strike and at maximal gust velocity are compared. An increased blade loading is detectable in the pressure coefficients which are displayed as contour plots. Moreover, the separation region on the blade root increases when the gust strikes the wind turbine
N Nikghazali - One of the best experts on this subject based on the ideXlab platform.
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performance investigation of a power augmented vertical axis wind turbine for urban high rise application
Renewable Energy, 2013Co-Authors: W T Chong, A Fazlizan, A Badarudin, N NikghazaliAbstract:A shrouded wind turbine system has a number of potential advantages over the conventional wind turbine. A novel power-augmentation-guide-vane (PAGV) that surrounds a Sistan wind turbine was designed to improve the wind Rotor performance by increasing the on-coming wind speed and guiding it to an optimum flow angle before it interacts with the Rotor blades. The integration of the PAGV into the 3-in-1 wind, solar and rain water harvester on high-rise buildings has been illustrated. A particular concern related to public safety is minimized when the wind turbine is contained inside the PAGV and noise pollution can be reduced due to the enclosure. Besides, the design of the PAGV that blends into the building architecture can be aesthetic as well. Moreover, a mesh can be mounted around the PAGV to prevent the bird-strike problem. From the wind tunnel testing measurements where the wind turbine is under free-running condition (only Rotor inertia and bearing friction were applied), the wind Rotor rotational speed (with the PAGV) was increased by 75.16%. Meanwhile, a computational fluid dynamics (CFD) simulation shows that the Rotor Torque was increased by 2.88 times with the introduction of the PAGV. Through a semi-empirical method, the power output increment of the Rotor with the PAGV was 5.8 times at the wind speed of 3 m/s. Also, the flow vector visualization (CFD) shows that a larger area of upstream flow was induced through the Rotor with the PAGV.
